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Bird song variations along an urban gradient: The case of the European blackbird (Turdus merula)
... Several studies have demonstrated that birds (mostly oscines) adjust the amplitude of signals (Brumm, 2004;Halfwerk and Slabbekoorn, 2009). Many birds increase the minimum frequency (Slabbekoorn and Peet, 2003;Fern andez-Juricic et al., 2005;Slabbekoorn and Den Boer-Visser, 2006;Nemeth and Brumm, 2009;Hu and Cardoso, 2010;Mendes et al., 2011;Ríos-Chel en et al., 2012b), maximum frequency (Mendes et al., 2011) and dominant frequency (Nemeth and Brumm, 2009;Parris and Schneider, 2009;Hu and Cardoso, 2010;Proppe et al., 2011Proppe et al., , 2012Luther and Derryberry, 2012;Lazerte et al., 2016Lazerte et al., , 2017. These changes in amplitude and frequency of signals lead to changes in the sound power distribution levels (Halfwerk and Slabbekoorn, 2009). ...
... Several studies have demonstrated that birds (mostly oscines) adjust the amplitude of signals (Brumm, 2004;Halfwerk and Slabbekoorn, 2009). Many birds increase the minimum frequency (Slabbekoorn and Peet, 2003;Fern andez-Juricic et al., 2005;Slabbekoorn and Den Boer-Visser, 2006;Nemeth and Brumm, 2009;Hu and Cardoso, 2010;Mendes et al., 2011;Ríos-Chel en et al., 2012b), maximum frequency (Mendes et al., 2011) and dominant frequency (Nemeth and Brumm, 2009;Parris and Schneider, 2009;Hu and Cardoso, 2010;Proppe et al., 2011Proppe et al., , 2012Luther and Derryberry, 2012;Lazerte et al., 2016Lazerte et al., , 2017. These changes in amplitude and frequency of signals lead to changes in the sound power distribution levels (Halfwerk and Slabbekoorn, 2009). ...
... The effects of noise on bird vocalizations and acoustic parameters have been evaluated in recent years. Studies have shown that in environments with high noise levels birds sing songs with higher frequency and amplitude, shorter songs, shorter notes/elements and fewer song notes/elements (Brumm, 2004;Mockford and Marshall, 2009;Nemeth and Brumm, 2009;Parris and Schneider, 2009;Hu and Cardoso, 2010;Salaberria and Gil, 2010;Mendes et al., 2011;Proppe et al., 2011Proppe et al., , 2012Luther and Derryberry, 2012;Ríos-Chel en et al., 2012b;Schuster et al., 2012;Huffeldt and Dabelsteen, 2013;Nemeth et al., 2013;Redondo et al., 2013;Lazerte et al., 2016Lazerte et al., , 2017. These studies aim to understand how bird species respond to high noise levels in rural and urban areas, either changing or not changing their vocalization. ...
The structure and organization of acoustic signals arise through evolutionary processes and adaptive pressures on each species. During learning, natural or anthropogenic factors, such as high noise levels in urban areas, pose challenges to acoustic communication in birds. Many species adjust their acoustic signals to higher noise levels by increasing the frequency of vocalizations. The objectives of this study were to compare the dominant frequency of songs among birds dwelling in forest fragments distant from and near to urban areas, establish correlations between the dominant frequency of song and noise levels in these environments and verified the difference of response between oscines, suboscines and non-passerines. We recorded vocalizations of birds between July/2013 and November/2014 in four forest fragments, two of them near and two distant from urban areas. We used Audacity software to measure the dominant frequency. We measured the ambient noise by a calibrated sound pressure level meter in decibels (dBA) in each of the forest fragments. We analyzed 3740 vocalizations of nine tropical bird species. Forest fragments near to urban areas have higher noise levels than more distant forest fragments. Eight of nine studied species presented higher dominant frequencies of songs in forest fragments near to urban areas. Only one species, Myiothlypis flaveola, did not change the dominant frequency of song between the four analyzed forest fragments. The difference in dominant frequency between the forest fragments distant and closer to the urban areas did not vary between oscines, suboscines and non-passerines. Eight tropical birds exhibited higher dominant frequencies of song in forest fragments near urban areas with high level of ambient noise. Oscine, suboscine and non-passerine showed song variations. Bird species that have differences in the vocalization dominant frequency can be used in environmental monitoring and in ethological studies, as they are sensitive to high noise levels. Noise pollution caused by the vehicular traffic and urbanization are correlates with changes in the vocalization of tropical birds in forest fragments.
... Furthermore, overall similarity in the spectral and temporal characteristics of the songs in neighbors can also increase with male competition (Laiolo and Tella 2005;Foote et al. 2008). Another possible effect of competition on the song of neighbors is that birds singing close to each other may change their song types (Vargas-Castro 2015) or the frequency of their songs to remain audible (Mendes et al. 2011;Hamao et al. 2016) and facilitate recognition, causing negative assortativity among individuals in the frequency characteristics of the song. ...
... Minimum frequency seems to be a flexible song trait that promotes audibility also at the within-species level. For example, European blackbirds (Turdus merula) and oriental magpie robins (Copsychus saularis) adjusted the maximum and minimum frequency of their songs to noise levels (Mendes et al. 2011;Hanafi et al. 2019 The negative assortativity in repertoire size is more puzzling. Repertoire size may be connected to individual quality (Garamszegi et al. 2007;Hegyi et al. 2010), and birds of similar quality may avoid settling near each other. ...
The position occupied in social networks influences the success of individuals in many animal species. However, the associations between bird song (an important means of communication) and the relative position in social networks remained understudied. Such associations are expected because neighbors can learn song elements from each other or change their songs due to competition, and also because song can be related to other individual traits determining social network positions. We investigated these phenomena in males of the collared flycatcher (Ficedula albicollis), a passerine with complex songs and intense territorial interactions. Relying on 19 years of song recordings, we used multiple traits reflecting the spectral and temporal characteristics and complexity of songs, as well as syllable composition, to investigate if similarity in song is associated with the position in neighbor networks. We also examined whether birds settle down in an age‐dependent manner (as age is linked to individual quality) and whether the nonrandom spatial distribution of song is affected by the proportion of immigrants, young birds, or the number of displaying males. We found that the minimum frequency and the repertoire size of neighbors differed, but this pattern was not shaped by the investigated predictors. Therefore, our results highlight the need to study communication traits and social environment together. The fact that neighboring males tend to sing differently with respect to some song traits suggests that songs can be flexibly adjusted based on the performance of conspecifics.
... This species performs striking choruses at dawn and dusk during the bird-breeding season in the city of La Paz and its surroundings. Furthermore, the study of species of the genus Turdus also allows comparison of responses to urbanization with congeneric species (e.g., [19,25,[36][37][38][39][40]). ...
... The increase in some song frequency parameters in urban environments is a widely reported response for several bird species around the world (e.g., [14,18,20,21]), but the increase in minimum frequency rather than entire song was mainly reported [19]. Previous studies with species of the genus Turdus reported an increase in one or more song frequency parameters in response to urbanization [19,25,[36][37][38][39][40]. To our knowledge, this is the first study for the genus Turdus to report that the frequency of the entire song increased. ...
Simple Summary
Urban noise imposes significant challenges for the acoustic communication of birds that are able to survive inside cities. Birds sing most intensely during two periods of the day called dawn and dusk choruses, and although various responses to the urbanization of dawn songs have been reported, very little attention was paid to the dusk chorus. Our objective is to evaluate in urban and non-urban populations of the Chiguanco Thrush (Turdus chiguanco), a very common bird in the city of La Paz (Bolivia) if there are differences between the songs of both choruses, and if these variations are altered by urbanization. Our results show that the loudness, frequency range and number of songs per individual are greater in the dawn chorus and that urban individuals must increase the frequency and loudness of their songs in both choruses to cope with urban noise. Urban Chiguanco Thrushes even produce less than half as many songs per individual compared to non-urban individuals, probably due to the high cost of increasing loudness and frequency. If wild birds are forced to modify their songs so much within the city, this should alert us to the possible negative effects of urban noise on human health.
Abstract
Urbanization is one of the more important phenomena affecting biodiversity in the Anthropocene. Some organisms can cope with urban challenges, and changes in birds’ acoustic communication have been widely studied. Although changes in the timing of the daily organization of acoustic communication have been previously reported, there is a significant gap regarding possible variations in song structure between dawn and dusk choruses. Considering that urbanization imposes different soundscapes for dawn and dusk choruses, we postulate two hypotheses: (i) there are variations in song parameters between dawn and dusk choruses, and (ii) such parameters within the city will vary in response to urban noise. We studied urban and extra-urban populations of Chiguanco Thrush in La Paz, Bolivia, measuring in dawn and dusk choruses: song length; song sound pressure level; minimum, maximum, range and dominant frequency; and the number of songs per individual. The results support our two hypotheses: there were more songs, and songs were louder and had larger band widths at dawn than at dusk in urban and extra-urban populations. Urban Chiguanco Thrushes sing less, the frequency of the entire song rises, and the amplitude increases as compared with extra-urban Chiguanco Thrushes. Understanding variations between dawn and dusk choruses could allow for a better interpretation of how some bird species cope with urban challenges.
... This species performs striking choruses at dawn and dusk during the bird-breeding season in the city of La Paz and its surroundings. Furthermore, the study of species of the genus Turdus also allows comparison of responses to urbanization with congeneric species (e.g., [19,25,[36][37][38][39][40]). ...
... The increase of some song frequency parameters in urban environments is a widely reported response for several bird species around the world (e.g., [14,18,20,21]), but the increase in minimum frequency rather than entire song was mainly reported [19]. Previous studies with species of the genus Turdus reported an increase in one or more song frequency parameters in response to urbanization [19,25,[36][37][38][39][40]. To our knowledge, this is the first study for the genus Turdus to report that the frequency of the entire song increased. ...
Urbanization in one of the more important phenomena affecting biodiversity in the Anthropocene. Some organisms can cope with urban challenges, and changes in birds’ acoustic communication have been widely studied. Although changes in the timing of the daily organization of acoustic communication have been previously reported, there is a significant gap regarding possible variations in song structure between dawn and dusk choruses. Considering that urbanization potentially imposes different soundscapes for the dawn and dusk choruses, we postulate two hypotheses: i) there are “natural” variations in song parameters between dawn and dusk choruses, and ii) such parameters within the city will vary in response to urban noise. We studied urban and extra-urban populations of Chiguanco Thrush in La Paz, Bolivia, measuring for their dawn and dusk choruses: song length, song sound pressure, minimum, maximum, range and dominant frequency, and the proportion of songs produced. The results support our two hypotheses: in natural and urban conditions dawn songs were louder and with larger bandwidths, and within the city, the frequency of the entire song rises along with increasing amplitude. Understanding structural variations between dawn and dusk choruses could allow for better interpretation of how some bird species cope with urban challenges.
... In contrast, species-level studies are less common (McDonnell and Hahs 2015). Relative to non-urban populations, animals from urban populations express altered behavior such as songs with distinct pitches or loss of migratory behavior (Evans et al., 2012;Mendes et al., 2011), changes in physiology such as lower glucocorticoid secretion in response to stress or higher oxidative stress (Partecke et al., 2006), earlier reproduction Partecke et al., 2004), faster circadian rhythm oscillations (Dominoni et al., 2013), higher parasitism rate (Bradley and Altizer, 2007) and/or differences in morphology (Liker et al., 2008;Weller and Ganzhorn, 2004). These shifts in lifehistory traits are often seen as a response, adaptive or not, to urban stressors. ...
... However, because cities are extremely diverse and because most studies are based on a single city and not multiple city replicates (but see Johnson et al., 2018), it is difficult to make general conclusions and identify a robust syndrome of urbanization for population-level traits. In addition, population studies are generally correlative Lazić et al., 2015;Leong et al., 2016;Liker et al., 2008;Lowe et al., 2014;Lu et al., 2006;Mendes et al., 2011;Scales et al., 2011;, and do not quantify the respective contributions of genetics and phenotypic plasticity. So far, common garden experiments (the rearing of individuals from different origins under the same environmental condition) between urban and non-urban populations highlighted a genetic basis for the lower dispersal ability of urban plants , earlier reproduction of urban birds and ants Partecke et al., 2004) and for specific behaviors of urban birds (lower migratory behavior, increased boldness and stress (Evans et al., 2012;Partecke et al., 2006)). ...
L’urbanisation est un processus qui a tendance à s’accroître ces dernières années. Les villes imposent un certain nombre de changements environnementaux aux espèces y vivants : températures élevées, habitat fragmenté, pollué (pollution lumineuse, acoustique et/ou chimique)…. Malgré leur importance écologique et économique, peu d’études se sont penchées sur la réponse des espèces eusociales à cette urbanisation. Ces espèces pourraient avoir des capacités de réponses aux changements environnementaux différentes des espèces solitaires, du fait de leur grande plasticité phénotypique et de leur vie en société. L’objectif de cette thèse est donc de déterminer comment l’eusocialité peut influencer sur la réponse à l’urbanisation. Dans une première partie, nous avons montré, à travers une expérience de jardin commun, que les colonies de Temnothorax nylanderi toléraient mieux un métal trace (le cadmium) que les colonies de forêt. Nous avons également trouvé une divergence des comportements de fourragement et d’agression chez ces populations. Dans une deuxième partie, nous avons mis en évidence un rôle des facteurs génétiques dans la meilleure tolérance des colonies urbaines au cadmium. Nous avons également effectué une expérience de cross fostering, afin de distinguer les effets des ouvrières de ceux des larves sur la meilleure tolérance au cadmium des colonies urbaines. Une absence de réponse différentielle au cadmium cette année-là nous a empêché de tester cette hypothèse, mais a permis de mettre en évidence un effet tampon social de la taille des colonie ainsi que ses limites. Enfin, le dernier chapitre nous a permis de mettre en évidence des variations intra-annuelles dans la réponse des espèces eusociales aux stresseurs. Cette thèse souligne l’importance de prendre en compte les traits propres aux espèces sociales dans la réponse de ces espèces aux changements environnementaux majeurs.
... En ville, les chants des oiseaux se retrouvent masqués par le bruit urbain qui porte sur une fréquence similaire (Halfwerk & Slabbekoorn, 2009). Afin d'assurer la communication pour la reproduction malgré le bruit ambiant, les mâles urbains chantent sur une fréquence plus haute que les mâles ruraux (Slabbekoorn & Ripmeester, 2008 ;Mendes et al, 2011). Leurs chants sont également plus rapides et plus courts (Slabbekoorn & den Boer-Visser, 2006). ...
... Cette réduction du succès reproducteur en présence de bruit urbain peut d'abord être liée à l'altération de la perception du chant par la femelle. En présence de bruit urbain, les mâles doivent chanter sur des fréquences plus hautes pour se faire entendre (Slabbekoorn & Ripmeester, 2008 ;Mendes et al, 2011). Or, les meilleurs mâles reproducteurs sont généralement ceux avec des chants de basse fréquence (Holveck & Riebel, 2010 ;. ...
L’urbanisation est l’un des phénomènes majeurs qui impactent la biodiversité à l’échelle mondiale. Les nombreuses contraintes associées au milieu urbain (perte d’habitat, changement des ressources, pollutions chimique, lumineuse et sonore, etc.) modifient la diversité et la répartition des espèces animales, et peuvent avoir de lourdes conséquences à l’échelle individuelle. Or, le développement constant du milieu urbain nécessite de mettre à jour les études sur les effets de ce milieu sur les espèces animales, et en particulier sur les oiseaux, qui rendent de nombreux services écosystémiques à l’homme. Dans ce contexte, nous avons cherché à étudier les bénéfices et contraintes du milieu urbain chez les oiseaux, en se plaçant à trois échelles différentes : biodiversité, population et individu. Dans un premier temps, nous avons réalisé une étude spatiale de la biodiversité aviaire à Niort. Nous avons pu mettre en évidence l’importance de maintenir des infrastructures vertes et connectées en ville, pour favoriser la présence des espèces communes comme celles moins adaptées au milieu urbain. Dans un deuxième temps, nous avons cherché à évaluer l’état des populations de moineaux domestiques en ville, ceux-ci étant en fort déclin dans les grandes villes européennes. À l’aide d’une étude corrélative, nous avons démontré que le milieu urbain est particulièrement stressant pour les moineaux en développement. Également, l’analyse d’un stress hydrique en conditions expérimentales nous a permis de constater que les moineaux adultes sont également très sensibles aux changements des conditions de l’environnement. Dans un troisième temps, l’application d’une contrainte du milieu urbain (pollution lumineuse) sur les moineaux au cours de la reproduction a permis de mettre en évidence des changements rapides du comportement individuel en réponse à cette contrainte. Les résultats de ces différentes approches démontrent que les effets de l’urbanisation sur les oiseaux sont complexes, et que les suivis démographiques doivent être associés à des études précises de l’habitat urbain et des contraintes associées pour mieux comprendre l’évolution des populations d’oiseaux en ville.
... Applying a gradient approach allows a higher resolution of environmental variables and conclusions that are more likely linked to urbanisation per se. Along with a higher proportion of sealed surface areas, human population density (Stankowski 1972) intensity of chemical pollution (Andrews 2008;Krommer et al. 2007;Mingorance & Oliva 2006;Simon et al. 2011), noise pollution (Mendes et al. 2011;Pijanowski et al. 2011), artificial light pollution (Cinzano et al., 2001(Cinzano et al., , 2007Hölker et al. 2010) and infectious diseases (Bradley & Altizer 2007;Giraudeau et al., 2014) are usually increasing along urbanisation gradients. Thus, there might be impacts from multiple origins (Isaksson 2015;Andrews 2008;Mendes et al. 2011;Cinzano et al. 2007). ...
... Along with a higher proportion of sealed surface areas, human population density (Stankowski 1972) intensity of chemical pollution (Andrews 2008;Krommer et al. 2007;Mingorance & Oliva 2006;Simon et al. 2011), noise pollution (Mendes et al. 2011;Pijanowski et al. 2011), artificial light pollution (Cinzano et al., 2001(Cinzano et al., , 2007Hölker et al. 2010) and infectious diseases (Bradley & Altizer 2007;Giraudeau et al., 2014) are usually increasing along urbanisation gradients. Thus, there might be impacts from multiple origins (Isaksson 2015;Andrews 2008;Mendes et al. 2011;Cinzano et al. 2007). ...
Urbanisation is proceeding at an alarming rate which forces wildlife to either retreat from urban areas or cope with novel stressors linked to human presence and activities. For example, urban stressors like anthropogenic noise, artificial light at night and chemical pollution can have severe impacts on the physiology of wildlife (and humans), in particular the immune system and antioxidant defences. These physiological systems are important to combat and reduce the severity of parasitic infections, which are common among wild animals. One question that then arises is whether urban-dwelling animals, whose immune and antioxidant system are already challenged by the urban stressors, are more susceptible to parasitic infections. To assess this, we studied nestlings of Eurasian kestrels ( Falco tinnunculus ) in Vienna, Austria, during 2015 and 2017. We measured biomarkers of innate immune function, oxidative stress and body mass index and ectoparasite infection intensity in 143 nestlings (from 56 nests) along an urban gradient. Nestlings in more urbanised areas had overall fewer ectoparasites, lower haemolysis (complement activity) and lower body mass index compared to nestlings in less urbanised areas. None of the other immune or oxidative stress markers were associated with the urban gradient. Despite some non-significant results, our data still suggest that kestrel nestlings experience some level of reduced physiological health, perhaps as a consequence of exposure to more urban stressors or altered prey availability in inner-city districts even though they had an overall lower ectoparasite burden in these heavily urbanised areas.
... Birds react to low-frequency ambient noise pressure in different ways (Brumm and Slabbekoorn 2005;Swaddle et al. 2015). Some have been shown to increase their minimum frequency (Slabbekoorn and den Boer-visser 2006;Brumm 2009, 2010;Hu and Cardoso 2010;Mendes et al. 2011;Ríos-Chelén et al. 2012), maximum frequency (Francis et al. 2011;Mendes et al. 2011) and others their dominant frequency (Nemeth and Brumm 2009;Hu and Cardoso 2010;Proppe et al. 2011Proppe et al. , 2012LaZerte et al. 2016LaZerte et al. , 2017Luther et al. 2016;de Tolentino et al. 2018) in response to background noise. Increases in frequency may, however, be a side effect of singing at higher amplitude in noisy environments (Nemeth and Brumm 2010) -the Lombard Effect Zollinger and Brumm 2011) -as amplitude and song frequency are often correlated (Beckers et al. 2003;Amador et al. 2008;Zollinger et al. 2012). ...
... Birds react to low-frequency ambient noise pressure in different ways (Brumm and Slabbekoorn 2005;Swaddle et al. 2015). Some have been shown to increase their minimum frequency (Slabbekoorn and den Boer-visser 2006;Brumm 2009, 2010;Hu and Cardoso 2010;Mendes et al. 2011;Ríos-Chelén et al. 2012), maximum frequency (Francis et al. 2011;Mendes et al. 2011) and others their dominant frequency (Nemeth and Brumm 2009;Hu and Cardoso 2010;Proppe et al. 2011Proppe et al. , 2012LaZerte et al. 2016LaZerte et al. , 2017Luther et al. 2016;de Tolentino et al. 2018) in response to background noise. Increases in frequency may, however, be a side effect of singing at higher amplitude in noisy environments (Nemeth and Brumm 2010) -the Lombard Effect Zollinger and Brumm 2011) -as amplitude and song frequency are often correlated (Beckers et al. 2003;Amador et al. 2008;Zollinger et al. 2012). ...
Effective communication in birds is often hampered by background noise, with much research focusing on the effect of anthropogenic noise on passerine bird song. Continuous low-pitch natural noise can drive changes in both spectral and temporal patterning of bird vocalisations, but the extent to which these effects may also affect birds that lack vocal learning is not well understood. We used a gradient of exposure to natural low-frequency noise to assess whether it exerts selective pressure on innate vocalisations. We tested whether three species of Pogoniulus tinkerbirds adapt their song when exposed to continuous low-frequency noise from ocean surf. We show that dominant frequency increases the closer birds are to the coast in at least two species, indicating that ocean surf sound may apply a selective pressure on songs. Tinkerbirds adapt their songs by increasing dominant frequency to avoid masking by ambient noise, therefore improving long-range communication. Our study provides evidence that natural ambient noise affects vocalisations in birds whose songs develop innately. We believe that our results can also be extrapolated in the context of anthro-pogenic noise pollution, hence providing a baseline for the study of the effects of low-frequency ambient noise on birds that lack vocal learning.
... In contrast, species-level studies are less common (McDonnell and Hahs 2015). Relative to non-urban populations, animals from urban populations express altered behavior such as songs with distinct pitches or loss of migratory behavior (Evans et al. 2012;Mendes et al. 2011), changes in physiology such as lower glucocorticoid secretion in response to stress or higher oxidative stress (Partecke et al. 2006), earlier reproduction (Chick et al. 2019;Partecke et al. 2004), Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11252-020-01060-9) contains supplementary material, which is available to authorized users. ...
... However, because cities are extremely diverse and because most studies are based on a single city and not multiple city replicates (but see Chick et al. 2019;Johnson et al. 2018), it is difficult to make general conclusions and identify a robust syndrome of urbanization for population-level traits. In addition, population studies are generally correlative (Chamberlain et al. 2009;Hof et al. 2016;Isaksson 2010;Lazić et al. 2015;Leong et al. 2016;Liker et al. 2008;Lowe et al. 2014;Lu et al. 2006;Mendes et al. 2011;Scales et al. 2011;Slabbekoorn and Boer-Visser 2006), and do not quantify the respective contributions of genetics and phenotypic plasticity. So far, common garden experiments (the rearing of individuals from different origins under the same environmental condition) between urban and non-urban populations highlighted a genetic basis for the lower dispersal ability of urban plants (Cheptou et al. 2008), earlier reproduction of urban birds and ants (Chick et al. 2019;Partecke et al. 2004) and for specific behaviors of urban birds (lower migratory behavior, increased boldness and stress: Evans et al. 2012;Partecke et al. 2006). ...
Cities can be used as in situ replicates to assess the responses of organisms to environmental changes, such as increased heat or pollution. Community-level studies and more rarely population-level studies have been conducted, but they are not often based on multiple city replicates, thus preventing generalization. Our study tested whether colonies of the ant Temnothorax nylanderi from forest and urban populations exhibit distinct responses to pollution. Because this is a social species, we could also test whether social traits (colony size and mean size of adult workers) affected the response of colonies to urbanization. We collected colonies from four pairs of forest and urban habitats and reared them in the laboratory under normal or cadmium-supplemented diets. We then measured the emergence rate and size of newly-produced workers as well as the mortality rate of adult workers. In all four forest/city replicates, urban colonies were less negatively affected by cadmium than forest colonies for emergence rate and size of newly-produced workers, but not for mortality rate of adult workers. We did not find any correlation between social traits and cadmium resistance, in contrast with what was found in other eusocial insects. We discuss the potential adaptive nature of this differential response.
... songs of Common Blackbirds have higher maximum frequencies in urban environments than in rural environments (Mendes et al. 2011). ...
... Birds may not be able to change the high frequencies of some elements because of the limitations imposed by their morphology and vocal production organs such as beak shape, trachea and syrinx that constrain the maximum frequencies that a bird can produce (Patricelli & Blickley 2006, Catchpole & Slater 2008. However, the Common Blackbird is one of the few species in which the maximum frequency of the whole song has presumably increased in response to anthropogenic noise, probably to avoid anthropogenic noise-masking (Mendes et al. 2011). ...
Anthropogenic noise (≤ 3 kHz) can affect key features of birds’ acoustic communication via two different processes: (1) song‐learning, because songbirds need to hear themselves and other birds to crystallize their song, and (2) avoidance of song elements that overlap with anthropogenic noise. In this study we tested whether anthropogenic noise reduces the number of song elements in the repertoire of House Wren Troglodytes aedon , an urban species. Additionally, we tested whether the proportion of high‐frequency elements (i.e. elements where the minimum frequency is above 3 kHz) is related to anthropogenic noise levels, and how the frequencies and duration of shared elements between males change with different levels of anthropogenic noise. We recorded 29 House Wren males exposed to different anthropogenic noise levels (36.50–79.50 dB) during two consecutive breeding seasons from four locations. We recorded each male on 2 days during each season continuously for 50 min (we collected 104 h of recordings) and measured anthropogenic noise levels every 10 min inside each male territory during the recording period. In general, individuals inhabiting noisier territories had smaller repertoires. However, only in two locations with anthropogenic noise levels between 38.60 and 79.50 dB did males inhabiting noisier territories have smaller repertoires. In the other two locations with lower anthropogenic noise (36.50–66.50 dB), the anthropogenic noise inside each territory was not related to the repertoire size. Individuals inhabiting the noisiest location showed a tendency to include more high‐frequency elements in their songs. In 26% of the elements, the anthropogenic noise affected their frequency features. Our results showed that not all House Wrens inhabiting urban environments modify their songs at the highest level of organization (i.e. repertoire) to reduce the masking effect of anthropogenic noise on acoustic communication.
... 60.0 dBA for daytime and 45.0 dBA for night time (Department of Environment Malaysia 2007). For birds that rely on vocalisation for territorial defence, searching for a mate and communication, anthropogenic noise has been found to affect their vocalisations (Lowry et al. 2013;Luther et al. 2016;Mendes et al. 2011;Potvin et al. 2011) and even reproductive rate (Halfwerk et al. 2011). ...
... Past studies have demonstrated that bird species altered their vocalisations in response to anthropogenic noise include House Finch (Carpodacus mexicanus) in Mexico (Bermúdez-Cuamatzin et al. 2009), Great Tit (Parus major) in Netherlands (Halfwerk and Slabbekoorn, 2009), Europe Blackbird (Turdus merula) in Spain (Mendes et al. 2011), Silvereye (Zosterops lateralis; Potvin et al. 2011) and Noisy Miner (Manorina melanocephala; Lowry et al. 2013) in Australia, Ash-throated Flycatcher (Myiarchus cinerascens; Francis et al. 2010) and Whitecrowned Sparrow (Zonotrichia leucophrys; Luther et al. 2016) in North America as well as White-breasted Whistler (Pachycephala lanioides) in Europe, North America and Australia (Hu & Cardoso 2009). Such behavioural adaptation occurs when signal transmission through vocalisation has been masked by anthropogenic noise. ...
... Two studies measuring noise conditions in the terrestrial environment (Mendes et al. 2011, Shieh et al. 2012 were also selected to illustrate how to compare reported sound levels and evaluate comparability. These studies examined how vocalizations change in response to increased noise for common blackbirds (Mendes et al. 2011) and cicadas (Shieh et al. 2012). ...
... Two studies measuring noise conditions in the terrestrial environment (Mendes et al. 2011, Shieh et al. 2012 were also selected to illustrate how to compare reported sound levels and evaluate comparability. These studies examined how vocalizations change in response to increased noise for common blackbirds (Mendes et al. 2011) and cicadas (Shieh et al. 2012). Like the marine examples, experiments were conducted in natural settings. ...
We present guidance we have developed and adapted through attempts to synthesize and distill the diverse literature documenting wildlife responses to noise into concise support for conservation planning. Our systematic review revealed significant inconsistencies in the use of—and specifications for—acoustic metrics. Studies typically report noise levels in decibels (dB), yet these values can arise from a diverse array of methods and processing procedures. Though some of this diversity reflects varied objectives and acoustical contexts, we believe that normative guidance and better awareness of standards would enhance the interpretation, repeatability of published studies, and incorporation of results into conservation planning. Nested within this larger issue is the vexing problem of calibration, especially in relation to consumer audio recorders or emerging products for bioacoustical monitoring. While it is possible to extract useful information about acoustic phenology or species presence from uncalibrated audio recordings, calibration can deliver a much broader range of information. We review the suite of calibration options presently available, and our experience with implementing and sharing solutions.
... De esta manera, el ruido que provocan diferentes actividades humanas interfiere en la comunicación acústica de las aves, causando error en la comunicación [7]. Como respuesta, algunas especies aumentan la frecuencia del canto, y se ha encontrado que este incremento ocurre en mayor proporción en las zonas urbanas, en comparación con las zonas periurbanas y rurales [5][6][7][8][9][10][11][12]. Esto ha sido documentado en las siguientes especies: Trichoglossus haematodus (Rainbow lorikeet) [8], Platycercus eximius (Eastern rosella) [8], Anthochaera carunculata (Red wattlebird) [8], Manorina melanophrys (Bell miner) [8], Cracticus torquatus (Grey butcherbird) [8], Troglodytes musculus (Southern House Wren) [9], T. troglodytes (Eurasian wren) [11], Turdus merula (Common blackbird) [8,10], Parus major (Great tit) [5], Melospiza melodía (Song sparrow) [12]. ...
... Como respuesta, algunas especies aumentan la frecuencia del canto, y se ha encontrado que este incremento ocurre en mayor proporción en las zonas urbanas, en comparación con las zonas periurbanas y rurales [5][6][7][8][9][10][11][12]. Esto ha sido documentado en las siguientes especies: Trichoglossus haematodus (Rainbow lorikeet) [8], Platycercus eximius (Eastern rosella) [8], Anthochaera carunculata (Red wattlebird) [8], Manorina melanophrys (Bell miner) [8], Cracticus torquatus (Grey butcherbird) [8], Troglodytes musculus (Southern House Wren) [9], T. troglodytes (Eurasian wren) [11], Turdus merula (Common blackbird) [8,10], Parus major (Great tit) [5], Melospiza melodía (Song sparrow) [12]. Así, el objetivo de este estudio fue determinar el efecto del ruido producido por el tráfico vehicular, en vías primarias, sobre las vocalizaciones de las especies de aves Cyclarhis gujanensis e Hylophilus flavipes en la zona de vida bosque seco tropical en el departamento del Tolima. ...
... Two studies measuring noise conditions in the terrestrial environment (Mendes et al. 2011, Shieh et al. 2012 were also selected to illustrate how to compare reported sound levels and evaluate comparability. These studies examined how vocalizations change in response to increased noise for common blackbirds (Mendes et al. 2011) and cicadas (Shieh et al. 2012). ...
... Two studies measuring noise conditions in the terrestrial environment (Mendes et al. 2011, Shieh et al. 2012 were also selected to illustrate how to compare reported sound levels and evaluate comparability. These studies examined how vocalizations change in response to increased noise for common blackbirds (Mendes et al. 2011) and cicadas (Shieh et al. 2012). Like the marine examples, experiments were conducted in natural settings. ...
ABSTRACT: Diverse biological consequences of noise exposure are documented by an extensive literature. Unfortunately, the aggregate value of this literature is compromised by inconsistencies in noise measurements and incomplete descriptions of metrics. These studies commonly report the noise level (in decibels, dB) at which a response was measured. There are many methods to characterize noise levels in dB, which can result in different values depending on the processing steps used. It is crucial that methods used for noise level measurement be reported in sufficient detail to permit replication and maximize interpretation of results, enable comparisons across studies, and provide rigorous foundations for noise management in environmental conservation. Understanding the differences in the acoustic measurements is vital when making decisions about acceptable levels or thresholds for conservation strategies, particularly for endangered species where mistakes can have irreversible consequences. Here we provide a discussion on how different acoustic metrics are derived and recommendations on how to report sound level measurements. Examples of additional measures of noise besides level (e.g. spectral composition, duration) are discussed in the context of providing further insight on the consequences of noise and will potentially help develop effective mitigation. It will never be possible to study all combinations of sources and species. Standardized methods of noise measurement and reporting are necessary to advance syntheses and general models that predict the ecological consequences of noise.
... De esta manera, el ruido que provocan diferentes actividades humanas interfiere en la comunicación acústica de las aves, causando error en la comunicación [7]. Como respuesta, algunas especies aumentan la frecuencia del canto, y se ha encontrado que este incremento ocurre en mayor proporción en las zonas urbanas, en comparación con las zonas periurbanas y rurales [5][6][7][8][9][10][11][12]. Esto ha sido documentado en las siguientes especies: Trichoglossus haematodus (Rainbow lorikeet) [8], Platycercus eximius (Eastern rosella) [8], Anthochaera carunculata (Red wattlebird) [8], Manorina melanophrys (Bell miner) [8], Cracticus torquatus (Grey butcherbird) [8], Troglodytes musculus (Southern House Wren) [9], T. troglodytes (Eurasian wren) [11], Turdus merula (Common blackbird) [8,10], Parus major (Great tit) [5], Melospiza melodía (Song sparrow) [12]. ...
... Como respuesta, algunas especies aumentan la frecuencia del canto, y se ha encontrado que este incremento ocurre en mayor proporción en las zonas urbanas, en comparación con las zonas periurbanas y rurales [5][6][7][8][9][10][11][12]. Esto ha sido documentado en las siguientes especies: Trichoglossus haematodus (Rainbow lorikeet) [8], Platycercus eximius (Eastern rosella) [8], Anthochaera carunculata (Red wattlebird) [8], Manorina melanophrys (Bell miner) [8], Cracticus torquatus (Grey butcherbird) [8], Troglodytes musculus (Southern House Wren) [9], T. troglodytes (Eurasian wren) [11], Turdus merula (Common blackbird) [8,10], Parus major (Great tit) [5], Melospiza melodía (Song sparrow) [12]. Así, el objetivo de este estudio fue determinar el efecto del ruido producido por el tráfico vehicular, en vías primarias, sobre las vocalizaciones de las especies de aves Cyclarhis gujanensis e Hylophilus flavipes en la zona de vida bosque seco tropical en el departamento del Tolima. ...
p>La hipótesis de adaptación acústica ha justificado que la estructura del hábitat y la intervención antrópica
son factores que influyen en la variación de las vocalizaciones de las aves. Este estudio estimó el efecto
del ruido del tráfico vehicular sobre las vocalizaciones de Hylophilus flavipes y Cyclarhis gujanensis. Se
efectuaron transectos paralelos a carreteras en dos localidades del bosque seco tropical del departamento
del Tolima; se realizó la grabación de sus cantos y la medición de la intensidad de ruido emitido por los
vehículos. Se encontró que H. flavipes y C. gujanensis emiten cantos con una frecuencia mínima mayor
cuando se encuentran en lugares donde la intensidad del ruido está por encima de los 40 dB. Así mismo, H. flavipes genera cantos con una menor duración de notas y una mayor duración entre notas, y tiende a cantar con menor número de notas cuando se ubican cerca de la carretera. Además, la última nota de los cantos de C. gujanensis tiende a ser más duradera bajo estas condiciones. Este estudio permitió determinar una variación en las vocalizaciones de las dos especies ante este factor, evidenciándose una respuesta mayor en H. flavipes que en C. gujanensis.</p
... These species can avoid the negative effects of noise and increase their population where other species cannot. Song adaptation has been described in different species by various authors; for example, the great tit, the blackbird [14,62,63], the European robin [31,64,65], and other species [23,66,67]. What is not clear is whether these changes are permanent or not [32,68,69]. ...
In an increasingly urbanized world, biodiversity, and more specifically, birdlife located in urbanized ecosystems, faces several threats. Among these, noise pollution has proven to be one of the most significant, as it affects the effectiveness and efficiency of acoustic communication. We studied the relationship between noise and the diversity and abundance of birds breeding in urban areas in the central region of the Iberian Peninsula (Spain). We analyzed how species diversity and density varied across three levels of noise pollution (high, medium, and low). Species diversity decreased in areas with high noise pollution as compared to sites with medium and low levels of noise. We analyzed the density of the most frequent species found within each category. We identified eight additional noise-tolerant species whose density had significantly increased in environments with high levels of noise (e.g., Blackbird, Eurasian Tree Sparrow, and the Coal Tit). The ten most sensitive species, such as the Common Linnet, House Sparrow, and the European Greenfinch, had significantly decreased densities when the level of noise increased. Identifying the sensitivity (the effect) of urban bird species to acoustic pollution is vital for effective conservation management measures and for the sustainable planning and management of cities.
... Significantly higher was the impact of noise pollution. A study published by Mendes et al. (2011) revealed changes in total frequency and frequency of sequences related to changes in ambient noise in rural areas versus urban areas and the time shift of vocalization in morning caused by anthropogenic impacts. Bergen and Abs (1997) found that Great Tit, Blue Tit, and Common Chaffinch Frontiers in Ecology and Evolution 11 frontiersin.org ...
Steadily increasing human population is changing the environment in many ways. One of the most disturbing impacts is the development of anthropogenic noise pollution connected to ever-growing traffic intensity. The road network can have both positive and negative effects on biodiversity and populations. Many bird species use acoustic communication to establish and maintain their territories and for intra-pair and adult–young communication. Noise pollution can impact negatively on breeding success and biorhythm if this communication is masked by noise and the individuals must adjust their singing activity. Yellowhammer (Emberiza citrinella) is a common bird species of agricultural landscapes whose population is declining due to agricultural intensification. It is found also in habitats near highways with forest steppe-like characteristics, where it is affected by the high levels of anthropogenic noise pollution. This study aimed to determine how this species adapts to noise from highway traffic by adjusting its singing activity. The influence of locality type, immediate and long-term impact of traffic noise on the average and total length of song sequences in the birdsong, and influence on the total number of recorded song sequences during the second hour after sunrise were evaluated in this study. Our results showed that Yellowhammer’s singing activity changed in localities close to highways compared to agricultural landscape. With increasing long-term traffic intensity on highways, song duration of the Yellowhammer song was decreasing. The present traffic intensity led to later onset of dawn chorus and decreasing strophe length with increasing number of passing vehicles. Furthermore, in the agricultural landscape, Yellowhammer’s song duration increased with increasing distance from the nearest road.
... Սև կեռնեխներն (Turdus merula) տիպիկ անտառային այն թռչնատեսակներից են, որոնք բարեհաջող յուրացրել են Եվրոպայի մի շարք ռեգիոններ, որտեղ ձևավորված պոպուլյացիաներն իրենց մի շարք էկոլոգիական, մորֆոֆիզիոլոգիական, էթոլոգիական առանձնահատկություններով տարբերվում են իրենց բնական լանդշաֆտների պոպուլյացիաներից [5,[8][9][10][11]: ...
The ecology of nesting common blackbirds in the territory of Stepanakert city, Artsakh are presented. Although common blackbirds are considered typical forest birds, due to their high ecological flexibility, they easily adapt to urban areas. Through observations, we found out that common blackbirds use about 23 species of plants and artificial structures for nesting in different parts of the city. Nests are built at an average height of 0,5-7 m from the ground, and both natural and anthropogenic materials are used as building materials.
... The impacts of urban noise, air pollution, and the built environment on residents and migrating birds have been extensively studied [SL15]. There is a strand of research that specifically analyze birdsong to discover if exposure to loud urban noise can lead to significant changes in their song traits and the time and frequency of their chorus, specifically since birds use different sounds to communicate, mate, and defend breeding territories and rely on the vocal communication to sustain their lives [MCRP11,Sla13]. One of the main challenges in the majority of bioacoustics and avian behavior studies is the costly and time-consuming nature of working with audio data, which limits the duration and geographical extent of the research. The application of machine learning in bird song classification is not new [MC97], but most of the developed models are trained using specific sets of data, limiting the user to a predefined set of labels, with no control over what the model perceives as bird songs. ...
Noise is one of the primary quality‐of‐life issues in urban environments. In addition to annoyance, noise negatively impacts public health and educational performance. While low‐cost sensors can be deployed to monitor ambient noise levels at high temporal resolutions, the amount of data they produce and the complexity of these data pose significant analytical challenges. One way to address these challenges is through machine listening techniques, which are used to extract features in attempts to classify the source of noise and understand temporal patterns of a city's noise situation. However, the overwhelming number of noise sources in the urban environment and the scarcity of labeled data makes it nearly impossible to create classification models with large enough vocabularies that capture the true dynamism of urban soundscapes. In this paper, we first identify a set of requirements in the yet unexplored domain of urban soundscape exploration. To satisfy the requirements and tackle the identified challenges, we propose Urban Rhapsody, a framework that combines state‐of‐the‐art audio representation, machine learning and visual analytics to allow users to interactively create classification models, understand noise patterns of a city, and quickly retrieve and label audio excerpts in order to create a large high‐precision annotated database of urban sound recordings. We demonstrate the tool's utility through case studies performed by domain experts using data generated over the five‐year deployment of a one‐of‐a‐kind sensor network in New York City.
... The impacts of urban noise, air pollution, and the built environment on residents and migrating birds have been extensively studied [SL15]. There is a strand of research that specifically analyze birdsong to discover if exposure to loud urban noise can lead to significant changes in their song traits and the time and frequency of their chorus, specifically since birds use different sounds to communicate, mate, and defend breeding territories and rely on the vocal communication to sustain their lives [MCRP11,Sla13]. One of the main challenges in the majority of bioacoustics and avian behavior studies is the costly and time-consuming nature of working with audio data, which limits the duration and geographical extent of the research. The application of machine learning in bird song classification is not new [MC97], but most of the developed models are trained using specific sets of data, limiting the user to a predefined set of labels, with no control over what the model perceives as bird songs. ...
Noise is one of the primary quality-of-life issues in urban environments. In addition to annoyance, noise negatively impacts public health and educational performance. While low-cost sensors can be deployed to monitor ambient noise levels at high temporal resolutions, the amount of data they produce and the complexity of these data pose significant analytical challenges. One way to address these challenges is through machine listening techniques, which are used to extract features in attempts to classify the source of noise and understand temporal patterns of a city's noise situation. However, the overwhelming number of noise sources in the urban environment and the scarcity of labeled data makes it nearly impossible to create classification models with large enough vocabularies that capture the true dynamism of urban soundscapes In this paper, we first identify a set of requirements in the yet unexplored domain of urban soundscape exploration. To satisfy the requirements and tackle the identified challenges, we propose Urban Rhapsody, a framework that combines state-of-the-art audio representation, machine learning, and visual analytics to allow users to interactively create classification models, understand noise patterns of a city, and quickly retrieve and label audio excerpts in order to create a large high-precision annotated database of urban sound recordings. We demonstrate the tool's utility through case studies performed by domain experts using data generated over the five-year deployment of a one-of-a-kind sensor network in New York City.
... Birds may be excluded on a purely acoustic basis from otherwise suitable habitats [30,36] , with the anthrophony (human-produced sounds) acting as a source of habitat degradation and fragmentation that affects the distribution of bird communities. This acoustic fragmentation, responsible for developing song differences between urban and non-urban birds of the same species [6,23,24,26,33] , may result in reproductive isolation [25] . ...
Urban green spaces provide natural habitat for birds in urban landscapes, yet the effects of noise and surrounding urban morphology on bird community structure and distribution are not well understood in Latin America, the second most urbanized region in the world. Santiago of Chile is the single city belonging to the Mediterranean ecosystem in South America and is subject to extensive urbanization as seen throughout Latin America. We examined the role of 65 urban green spaces (6 large: PAR and 59 small: SGS) in harboring native birds during winter 2019, analyzing the quality of green areas in terms of vegetation (i.e. NDVI, native vegetation, and tree cover), exotic bird species, noise levels, and surrounding urban matrix (i.e. building height and cover). Significantly higher noise levels were detected in SGS, along with significantly greater exotic bird (n=4) richness and abundance than PAR, which possessed significantly greater native bird (n=25) richness and abundance. Native birds were more abundant than exotic birds in green spaces with average noise levels < 52 dB and average NDVI > 0.5. Occupancy models indicate that green space occupancy by 50% of modeled native bird species was influenced by maximum noise levels, playing a larger role than vegetation (30%) and the urban matrix (0%). We stress the importance of developing networks of large green spaces in rapidly urbanizing regions, with abundant tree cover, surrounded by smaller urban morphology, and regulating noise levels to ensure the conservation of native bird communities in cities, particularly those that are threatened.
... Many environmentally sensitive traits in animals, including hormones (Fokidis et al. 2009;Bonier 2012;Dominoni et al. 2013), antioxidant levels (Møller et al. 2010;, immunity (Bailly et al. 2016), disease , behavior (Blumstein et al. 2005), and reproductive phenology (Davies and Deviche 2014) are known to be affected by urbanization. Thus, it is not surprising that urban activities can disrupt expression of condition-dependent animal signals including bird song (Mendes et al. 2011) and coloration (e.g. Jones et al. 2010;Hasegawa et al. 2014). ...
Historically, studies of condition-dependent signals in animals have been male-centric, but recent work suggests that female ornaments can also communicate individual quality (e.g., disease state, fecundity). There also has been a surge of interest in how urbanization alters signaling traits, but we know little about if and how cities affect signal expression in female animals. We measured carotenoid-based plumage coloration and coccidian (Isospora spp.) parasite burden in desert and city populations of house finches Haemorhous mexicanus to examine links between urbanization, health state, and feather pigmentation in males and females. In earlier work, we showed that male house finches are less colorful and more parasitized in the city, and we again detected such patterns in this study for males; however, urban females were less colorful, but not more parasitized, than rural females. Moreover, contrary to rural populations, we found that urban birds (regardless of sex) with larger patches of carotenoid coloration were also more heavily infected with coccidia. These results show that urban environments can disrupt condition-dependent color expression and highlight the need for more studies on how cities affect disease and signaling traits in both male and female animals.
... For example, the American Robin (Turdus migratorius) shows high levels of nocturnal vocal activity in environments contaminated with anthropogenic light, but in unlit areas, the species does not vocalise after dark (Miller 2006). However, this behaviour may also be related to the impact of anthropogenic noise in urban areas, where birds start singing earlier to prevent their vocalisations from being masked by noise (Mendes et al. 2011). Thus, lighting seems to be only one factor affecting nocturnal vocalisation in diurnal birds. ...
Many bird species have experienced short- or long-term population declines. However, the mechanisms and reasons underlying such negative changes are often not fully understood, making it difficult to identify effective conservation measures to recover populations. In this study, we focused on local changes in the abundance and distribution of calling male Corncrakes Crex crex in relation to: (1) within- and between-season site fidelity of adult males, (2) spatial distribution of territories in consecutive years and (3) the effect of habitat conditions on population size. We counted the number of calling males at ten randomly selected study plots (1 km2) in 2014–2018. Additionally, males were caught and individually marked in years 2015–2017. We found significant between-year changes in Corncrake abundance, from a 34% decrease to a 21% increase. On average, 32% of males established territories in the same locations as males recorded in the previous year. Breeding site fidelity was very low, with only 2–5% of males recaptured in the following year. Males selected areas characterized by higher values of NDVI (Normalized Difference Vegetation Index–higher values indicate more biomass) than on average within the study area. Population size in a particular year was significantly affected by the NDVI of the previous year but not by the NDVI in the current breeding season. We suppose that Corncrakes may exhibit a nomadic breeding behavior, and settle at territories when they encounter optimal habitat conditions. Moreover, as population size was negatively correlated with habitat conditions at the beginning of the previous breeding season, we suppose that local population changes may reflect more general trends in a whole population rather than local breeding success. Therefore, we highlight the need for better knowledge of Corncrake dispersal within the main European population and for the coordination of monitoring and conservation efforts, especially in those regions where most Corncrakes breed.
... For example, the American Robin (Turdus migratorius) shows high levels of nocturnal vocal activity in environments contaminated with anthropogenic light, but in unlit areas, the species does not vocalise after dark (Miller 2006). However, this behaviour may also be related to the impact of anthropogenic noise in urban areas, where birds start singing earlier to prevent their vocalisations from being masked by noise (Mendes et al. 2011). Thus, lighting seems to be only one factor affecting nocturnal vocalisation in diurnal birds. ...
Most bird species sing by day, with two distinct peaks of vocal activity—around sunrise and sunset. However, even typically diurnal birds also sing during at night what is for them an atypical part of the day. To date, the mechanism and function(s) of such behaviour remain unclear across bird taxa. In our study we focused on night singing by diurnal birds in two different types of environments—forests and open areas in eastern Poland. We examined: (1) which diurnal species sing at night (defined as the period between astronomical dusk and dawn); (2) how intensively different species vocalise at night; and (3) whether the occurrence of nocturnal singing by diurnal birds depends on the type of environment. To do this, we used autonomous sound recorders to record soundscapes in 27 points located in open habitats and 27 points located in forests. At each location the recorder continuously collected data for an entire day during the breeding season, from one hour before dawn to 10 AM the next day. All night songs were classified to their species of origin via manual spectrogram scanning. We recorded 88 bird species in total (12 orders, 32 families), of which 24 species (7 orders, 15 families) sang at night. Night singing was observed significantly more often in open areas than in forests. The frequency and intensity of night singing was species-specific and ranged from occasional singing to regular and intense singing. We hypothesise that elevated light levels have a crucial influence on night singing, but that the effect of light may also be modified by environmental factors (e.g., predator pressure).
... Among the best studied behavioral modifications of urban birds, those focused on acoustic communication head the list (Brumm, 2004;Slabbekoorn & Peet, 2003;Slabbekoorn, 2013). Most avian vocal adjustments in urban areas have been related to anthropogenic noise and artificial light at night, while other urban hazards have been largely neglected (Gorissen, Snoeijs, Van Duyse, & Eens, 2005;Mendes, Colino-pollution by adjusting song frequencies or changing the timing of their singing routines to avoid communication masking (Halfwerk, Lohr, & Slabbekoorn, 2018;Luther & Gentry, 2013;Slabbekoorn & Peet, 2003;Slabbekoorn, 2013;Warren, Katti, Ermann, & Brazel, 2006). Moreover, birds living in light polluted areas have shown to adjust their singing routines (Da Silva & Kempenaers, 2017;Gaston et al., 2017;Miller, 2006). ...
Living in the city represents a great challenge for organisms that are exposed to the novel environmental conditions inherent to urbanization. Recent studies have highlighted the ecological impact that urbanization poses on the acoustic phenotype and singing routines of birds. However, the organization and structure of avian dawn choruses in urban settings remains largely unexplored. In this study, we assessed the temporal structure of avian dawn choruses in an intra-urban area and a peri-urban forest using bipartite network analyses. We predicted a random network structuring of dawn choruses across time at the intra-urban area, while expected a non-random structure (i.e., modular or nested) at the peri-urban forest. While we detected different groups of birds vocalizing together temporarily, following a modular pattern in both studied conditions, only the one from the peri-urban forest showed a sequential temporal structure of dawn choruses. Avian dawn choruses from both intra-urban and peri-urban areas were mainly comprised by phylogenetically unrelated species (i.e., random phylogenetic structure), also exhibiting low overlap on singing frequencies. Our results are in agreement with the temporal partitioning of the acoustic space in the peri-urban forest. Our findings also suggest that the absence of temporally -structured modules of bird dawn choruses at heavily-urbanized areas could be related to the depau-perization of the avian community at intra-urban areas as a sequel of ecological filtering, as well as the consequent importance of the dominance of the acoustic space by invasive species.
... It might be that traffic noise at 60 dB was insufficient to stimulate adjustments in the social calls in V. sinensis. Indeed, previous studies in several taxa (Hotchkin and Parks 2013;Mendes et al. 2011), including bats Luo et al. 2015b) have shown that increases in signal duration depend on background noise amplitude. Alternatively, it was possible that V. sinensis altered other parameters of social calls (e.g., signal complexity and call amplitude) to cope with the masking effects of traffic noise. ...
Natural background noises are common in the acoustic environments in which most organisms have evolved. Therefore, the vocalization and sound perception systems of vocal animals are inherently equipped to overcome natural background noise. Human-generated noises, however, pose new challenges that can hamper audiovocal communication. The mechanisms animals use to cope with anthropogenic noise disturbances have been extensively explored in a variety of taxa. Bats emit echolocation pulses primarily to orient, locate and navigate, while social calls are used to communicate with conspecifics. Previous studies have shown that bats alter echolocation pulse parameters in response to background noise interference. In contrast to high-frequency echolocation pulses, relatively low-frequency components within bat social calls overlap broadly with ambient noise frequencies. However, how bats structure their social calls in the presence of anthropogenic noise is not known. Here, we hypothesized that bats leverage vocal plasticity to facilitate vocal exchanges within a noisy environment. To test this hypothesis, we subjected the Asian particolored bat, Vespertilio sinensis, to prerecorded traffic noise. We observed a significant decrease in vocal complexity (i.e., an increased frequency of monosyllabic calls) in response to traffic noise. However, an increase in the duration and frequency of social calls, as have been observed in other species, was not evident. This suggests that signal simplification may increase communication efficacy in noisy environments. Moreover, V. sinensis also increased call amplitude in response to increased traffic noise, consistent with the predictions of the Lombard effect.
... The European blackbird is a widespread and abundant species all over the Western Palearctic. Thanks to its diverse habitat use, blackbird populations are found in high densities both in urban and non-urban environments making this species an excellent model to understand ecological and behavioral adaptations to the urban life (Partecke et al., 2006;Ripmeester et al., 2010;Mendes et al., 2011;Nemeth et al., 2013). In this study, we have focused on two blackbird populations living in a riparian forest along the Jarama river near Madrid. ...
Noise pollution has a strong impact on wildlife by disrupting vocal communication or inducing physiological stress. Songbirds are particularly reliant on vocal communication as they use song during territorial and sexual interactions. Birds living in noisy environments have been shown to change the acoustic and temporal parameters of their song presumably to maximize signal transmissibility. Also, research shows that birds advance their dawn chorus in urban environments to avoid the noisiest hours, but little is known on the consequences of these changes in the time they spent singing at dawn. Here we present a comprehensive view of the European blackbird singing behavior living next to a large airport in Madrid, using as a control a population living in a similar but silent forest. Blackbird song is composed of two parts: a series of loud low-frequency whistles (motif) and a final flourish (twitter). We found that airport blackbirds were more likely to sing songs without the twitter part. Also, when songs included a twitter part, airport blackbirds used a smaller proportion of song for the twitter than control blackbirds. Interestingly, our results show no differences in song frequency between airport and control populations. However airport blackbirds not only sang earlier but also increased the time they spent singing when chorus and aircraft traffic overlapped on time. This effect disappeared as the season progressed and the chorus and the aircraft traffic schedule were separated on time. We propose that the typical urban upshift in frequency might not be useful under the noise conditions and landscape structure found near airports. We suggest that the modifications in singing behavior induced by aircraft noise may be adaptive and that they are specific to airport acoustic habitat. Moreover, we found that adjustment of singing activity in relation to noise is plastic and possibly optimized to cope with aircraft traffic activity. In a soundscape characterized by intermittent and strong noise bursts, singing for longer could be more advantageous than modifying frequency parameters, although it is likely more costly.
... La ciudad presenta niveles de ruido elevados, pero la diversidad de árboles y superficie de los parques podrían servir de atenuación mediante recursos tróficos y de nidificación, haciendo la ciudad favorable para la especie. Al ser una especie omnívora, la riqueza de frutos en parques y otros alimentos de origen antrópico, explicarían una población estable con buen éxito de cría (Luniak, Mulsow, & Walasz, 1990), un aumento del sedentarismo (Partecke & Gwinner, 2007), y una prolongada temporada reproductora (Partecke, Van't Hof, & Gwinner, 2004); aspectos que ocurren en otras especies de Turdidae (Mendes, Colino-Rabanal, & Peris, 2011b), e influirían en la adaptación del T. leucomelas en centros urbanos. ...
Anthropogenic noise in urban environments is a major challenge for those species that depend on the transmission of acoustic signals to communicate. To avoid being masked by background noise, some bird species are able to make adjustments in their songs. Studies on vocal adjustment for tropical birds are still scarce and are of interest since both the urban structure and the vegetation associated with urban habitats differ significantly with respect to the cities of temperate climates. In this research we studied the changes in the song parameters of the pale-breasted thrush (Turdus leucomelas) in an urban environment of the metropolitan area of Belém (Brazil). To this end, bird songs were recorded and ambient noise was measured between September and November 2008, in three different acoustic environments (urban, suburban and rural) along an urban gradient. The songs of 12 individuals per area were selected (a total of 36). Possible differences between song parameters were analyzed by ANOVAs. To assess the noise impact on bird song, we only considered the spectrum of environmental noise within the range of vocalizations of the species. In general, birds of urban habitats presented songs with higher maximum frequencies and with a wider range of notes, than their counterparts in suburban and rural areas. The differences were more pronounced in relation to rural areas. No differences in the minimum frequencies, the concentration of energy, or the average duration of the notes were found. These results differ from other studies and could possibly indicate variations in the way birds try to succeed in habitats with high ambient noise. It is necessary further exploration on the role of these changes in the effective improvement of intra-specific communication for the species in such environments.
... A lower effect level could explain why wrens show no increase in its minimum frequencies in order to avoid being masked by background noise. Vocal adjustment based on an increment in minimum frequencies is reported for species with low-frequency songs; Great Tit Parus major or Common Blackbird Turdus merula (Slabbekoorn & Peet 2003, Mendes et al. 2011a. ...
Birds inhabiting urban areas have to deal with high levels of ambient noise. Some species show a certain song flexibility that enables them to reduce noise interferences in their communications. This vocal adjustment usually implies an increase in the minimum frequencies of songs. Since urban noise is mainly made up of low frequencies (about 2.5-3.5 kHz), song of species that sing at higher frequencies could be less susceptible to being masked by anthropogenic noise. This study explores whether such species also show any kind of adjustment to noisy environments. For this purpose, the spectral and temporal parameters (note duration, maximum and minimum frequency and diversity) of the song of the European Wren Troglodytes troglodytes were analysed in three different environments (urban, periurban and rural). To evaluate the impact of noise on the vocalizations, a specific acoustic descriptor of song variability was developed. Song variability increased along the urban noise gradient from rural to urban areas and the duration of notes decreased from rural to urban zones. Urban wrens developed more complex songs with higher frequencies and longer notes than their rural counterparts, whereas peri-urban birds occupied an intermediate position, although closer to urban ones in the length of notes. These changes could be associated with higher background noise levels, although other possible causes, such as the population density, could also explain them. Maximum frequencies were mostly outside the background noise range and differed among habitats, whereas lower frequencies unexpectedly did not differ among habitats. Our results suggest that differences in song parameters among species may lead to different mechanisms of vocal adjustment. Even in wrens, with high frequency vocalisation, interference with urban anthropogenic noise could show certain changes in their vocalizations.
... A lower effect level could explain why wrens show no increase in its minimum frequencies in order to avoid being masked by background noise. Vocal adjustment based on an increment in minimum frequencies is reported for species with low-frequency songs; Great Tit Parus major or Common Blackbird Turdus merula (Slabbekoorn & Peet 2003, Mendes et al. 2011a. ...
Urban wrens developed more complex songs with higher frequencies and longer notes than their rural counterparts, whereas peri-urban birds occupied an intermediate position, although closer to urban ones in the length of notes. These changes could be associated with higher background noise levels, although other possible causes, such as the population density, could also explain them. Maximum frequencies were
mostly outside the background noise range and differed among habitats, whereas lower frequencies unexpectedly did not differ among habitats. Our results suggest that differences in song parameters among species may lead to different mechanisms of vocal adjustment. Even in wrens, with high frequency vocalisation, interference with urban anthropogenic noise could show certain changes in their vocalizations.
... Despite many different responses to noise that are possible, the vast majority of studies related to bird song parameters have focused on the changes in song frequency during exposure to noise (e.g. Slabbekoorn & den Boer-Visser 2006;Mendes et al. 2011;Redondo et al. 2013). Recent studies, however, have questioned the validity of the methods used for assessing frequency shifts (Zollinger et al. 2012;Nemeth et al. 2013;R ıos-Chel en et al. 2013). ...
The majority of male songbirds have small repertoires and sing with eventual variety; that is, they present one song type several times before switching to the next one. Several hypotheses have been proposed to
explain this phenomenon. The antiexhaustion hypothesis argues that song-type switching prevents muscle fatigue in the syrinx. The signal redundancy hypothesis suggests that repeating the same signal increases
transmission success. Here, we have studied the song behaviour of the chaffinch, Fringilla coelebs, a common Eurasian species in which the males sing a few different song types and provide eventual variety. We tested different hypotheses to explain the temporal organisation of song output (repertoire size, song rate, bout duration, etc.) as a function of ambient noise by comparing birds from the same macrogeographic region in which the birds live either in a noisy town (n = 71) or in a quieter forest habitat (n = 68). Contrary to the prediction of the signal redundancy hypothesis and the results of earlier work on chaffinches living close to noisy streams, we found no significant differences in song characteristics between the town and forest populations. Our results support the antiexhaustion hypothesis because males with larger repertoires were able to sing with a significantly higher rate due to faster switching between different song types and producing shorter bouts. Sample size or population differences between our study and earlier investigations of the same species may explain the inconsistency with previous findings. Future studies should focus on determining the relations between song organisation and the directly measured quality of males and females’ choice using, preferably, a longitudinal approach.
... These studies have revealed tremendous interspecific variation in responses to urbanization. For example, urbanization may influence vocalizations in some birds (Leonard and Horn 2008;Slabbekoorn and Ripmeester 2008;Mendes et al. 2011), the timing of nesting in others (Schoech and Bowman 2001), and cause local extinction in others (Blair 2001;Marzluff 2001;McKinney 2008). Thus, comparative studies on a wider variety of species are needed. ...
... También la biodiversidad y los efectos que los factores humanos tienen sobre las comunidades vegetales y animales han centrado distintos objetivos de investigación (ej. Buján et al., 1998;Dana et al., 2002;Murgui, 2009;Mendes et al., 2011). Sin embargo, gran número de hábitats y comunidades de los espacios urbanos siguen siendo aún desconocidos, y la ecología urbana se presenta como una disciplina con un amplio campo de investigación y desarrollo para hacer frente a estos retos. ...
Urban ecology examines processes and interactions between urban ecosystems and their biophysical and immediate human environment. These ecosystems host vegetated areas with high levels of biodiversity and also provide several goods and services to society. The purpose of this study is to develop a theoretical framework based on a review of relevant literature on urban ecology and urban vegetation. A scenario that allows an integrative approach to urban ecosystems and especially to domestic gardens is developed.
Urban environments pose novel challenges to signal communication of Urban-adjusted birds. The present study compared spectral and temporal traits of Common Myna (Acridotheres tristis) dwelling in Semirural and Urban sites in terms of Low, High, and Peak frequencies and syllable duration. We recorded 270 calls from approximately 224 individuals from 3 sites2 urban and one semirural, 90 calls from each area. We also correlated the Temperature and Humidity with each of these parameters using the Pearson correlation coefficient at 95% CI. Calls were found to be of higher frequencies in the Metropolitanurban area than in the semirural area. One-way ANOVA analysis showed significant differences (P<0.05) in all call parameters among the sites. Peak frequency was found to be slightly higher in the Semirural area as compared to the noisy urban site by about 45 Hz, but less as compared to the Metropolitan area of Ahmedabad. Syllable duration was highest in semirural area. Temperature and Humidity did not have a significant impact on birdsong (P>0.05). Our study emphasises urban environment affects both spectral and temporal traits of birdsong significantly and forms the primer for studying the effects of weather on birdsong. Urban Canyon effects and urban composition have more impact on signal transmission and communication as compared to weather parameters. However, additional study will be required to emphasise the quantification of impervious surfaces and noise levels and consider recording distance while making Urban and semirural comparisons.
Artificial light at night (ALAN) and noise pollution in urban ecosystems change the behavior of birds in many ways, one of these being in their singing. These changes are crucial because singing is highly important in bird communication. As birds rely on the spread of acoustic information, they were found to modify their singing activity in urban areas under the influences of artificial light at night and noise. They can adjust their behavior to the rhythm of night and day (e.g., by timing their dawn song according to changing light intensities or shifting their singing to higher frequencies to prevent possible masking of the signal by noise). In this study, we assessed the effects of light pollution, noise, day in the year, and meteorological variables on the morning and evening timing and duration of singing in blackbirds. We found that light and noise pollution significantly affect the onset of blackbird dawn singing. Blackbirds started singing earlier in localities with ALAN and noise pollution. The effects of light and noise pollution on the morning song of the blackbird diminish through the breeding season after peaking at the beginning of the nesting season; and they are only minimal on the evening vocal activity of this species. With growing intensity of noise pollution, the influence of light pollution also increases. Light and noise pollution have greater influence on the morning vocal activity of blackbirds than do current weather conditions.
In an increasingly urbanized world, biodiversity, and more specifically birdlife located in urbanized ecosystems, faces several threats. Among these, noise pollution has proven to be one of the most significant, as it affects the effectiveness and efficiency of acoustic communication. We studied the relationship between noise and the diversity and abundance of birds breeding in urban areas in the central region of the Iberian Peninsula (Spain). We analyzed how species diversity and density varied across three levels of noise pollution (high, medium, and low). Species diversity decreased in areas with high noise pollution as compared to the sites with medium and low levels of noise. We analyzed the density of the most frequent species found within each category. We identified eight additional noise-tolerant species, whose density had significantly increased in environments with high levels of noise (e.g. Blackbird, Eurasian Tree Sparrow, and the Coal Tit). The ten most sensitive species, such as the Common Linnet, House Sparrow, and the European Greenfinch, had significantly decreased densities when the level of noise increased. Identifying the sensitivity (the effect) of urban bird species to acoustic pollution is vital for effective conservation management measures and for the sustainable planning and management of cities.
The shifts of bird song frequencies in urbanized areas provide a unique system to understand avian acoustic responses to urbanization. Using passive acoustic monitoring and automatic bird sound recognition technology, we explored the frequency variations of six common urban bird species and their associations with habitat structures. Our results demonstrated that bird song frequencies in urban areas were significantly higher than those in peri-urban and rural areas. Anthropogenic noise and habitat structure were identified as crucial factors shaping the acoustic space for birds. We found that noise, urbanization, and open understory spaces are factors contributing to the increase in the dominant frequency of bird sounds. However, habitat variables such as vegetation density and tree height can potentially slow down this upward trend. These findings offer essential insights into the behavioral response of birds in a variety of urban forest habitats, with implications for urban ecosystem management and habitat restoration.
Anthropogenic noise is a major global pollutant but its effects on primates are poorly understood, limiting our ability to develop mitigation actions that favor their welfare and conservation. In this study, we used an experimental approach to determine the impact of variation in noise intensity on mantled howler monkeys ( Alouatta palliata ). We conducted the study at Los Tuxtlas (México), where we studied the physiological stress (proxied via fecal glucocorticoid metabolites, fGCM) and behavioral responses of 16 males. We played back chainsaw noise at two intensities (40 and 80 dB) and used days in which groups were not exposed to noise as matched controls. With increased noise intensity fGCM increased, vigilance and vocalizations were longer, and vigilance, vocalizations, and flight occurred quicker. Physiological and behavioral responses occurred even after low‐intensity noise playbacks (i.e., 40 dB). Therefore, noise intensity is a significant factor explaining the responses of mantled howler monkeys to anthropogenic noise. These results imply that management actions aimed at eradicating anthropogenic noise are required for the conservation and welfare of mantled howler monkeys at Los Tuxtlas.
Urbanization has dramatic impacts on natural habitats and such changes may potentially drive local adaptation of urban populations. Behavioral change has been specifically shown to facilitate fast adaptation of birds to changing environments, but few studies have investigated the genetic mechanisms of this process. Such investigations could provide insights into questions about both evolutionary theory and management of urban populations. In this study, we investigated whether local adaptation has occurred in urban populations of a Neotropical bird species, Coereba flaveola, specifically addressing whether observed behavioral adaptations are correlated to genetic signatures of natural selection. To answer this question, we sampled 24 individuals in urban and rural environments, and searched for selected loci through a genome-scan approach based on RADseq genomic data, generated and assembled using a reference genome for the species. We recovered 46 loci as putative selection outliers, and 30 of them were identified as associated to biological processes possibly related to urban adaptation, such as the regulation of energetic metabolism, regulation of genetic expression and changes in the immunological system. Moreover, genes involved in the development of the nervous system showed signatures of selection, suggesting a link between behavioral and genetic adaptations. Our findings, in conjunction with similar results in previous studies, support the idea that cities provide a similar selective pressure on urban populations and that behavioral plasticity may be enhanced through genetic changes in urban populations.
Urbanization can affect species communication by introducing new selection pressures, such as noise pollution and different environmental transmission properties. These selection pressures can trigger divergence between urban and non-urban populations. Songbirds rely on vocalizations to defend territories and attract mates. Urban songbirds have been shown in some species and some populations to increase the frequencies, reduce the length and change other temporal features of their songs. This study compares songs from four urban and three non-urban populations of dark-eyed juncos ( Junco hyemalis ) throughout Southern California. We examined song length, trill rate, minimum frequency, maximum frequency, peak frequency and frequency bandwidth. We also compared songs recorded from one urban junco population in San Diego nearly two decades ago with recently collected data in 2018–2020. Over all comparisons, we only found significant differences between UCLA and the 2006/2007 UCSD field seasons in minimum and maximum frequencies. These findings partially support and are partially in contrast to previous urban song studies. As urban areas expand, more opportunities will arise to understand urban song divergence in greater detail.
Urban green spaces provide natural habitat for birds in urban landscapes, yet the effects of noise and surrounding urban morphology on bird community structure and distribution are not well understood in Latin America, the second most urbanized region in the world. Santiago of Chile is the single city belonging to the Mediterranean ecosystem in South America and is subject to extensive urbanization as seen throughout Latin America. We examined the role of 65 urban green spaces—6 large urban parks (PAR) and 59 small green spaces (SGS)—in harboring native birds during winter 2019, analyzing the quality of green areas in terms of vegetation (i.e. NDVI, native vegetation, and tree cover), exotic bird species, noise levels, and surrounding urban morphology (i.e. building height and cover). Significantly higher noise levels were detected in SGS, along with significantly greater exotic bird (n = 4) richness and abundance than PAR, which possessed significantly greater native bird (n = 25) richness and abundance. Native birds were more abundant than exotic birds in green spaces with average noise levels < 52 dB and average NDVI > 0.5. Occupancy models indicate that green space occupancy by 50% of modeled native bird species was influenced by maximum noise levels, playing a larger role than vegetation (30%) and urban morphology (0%). We stress the importance of developing networks of large green spaces in rapidly urbanizing regions, with abundant tree cover, surrounded by smaller urban morphology, and regulating noise levels to ensure the conservation of native bird communities in cities, particularly those that are threatened.
Urban green spaces provide natural habitat for birds in city landscapes, yet the effects of noise and surrounding urban morphology on bird community structure and distribution are not well understood in Latin America, the second most urbanized region in the world. Santiago, Chile, located in the epicenter of the single portion of Mediterranean ecosystem in South America, is subject to extensive urbanization seen throughout Latin America. We examined the role of 65 urban green spaces (6 large: PAR and 59 small: SGS) in harboring native birds during winter 2019, analyzing the quality of green areas in terms of vegetation (i.e. NDVI, native vegetation, and tree cover), exotic bird species, noise levels, and surrounding urban matrix (i.e. building height and cover). Significantly higher noise levels were detected in SGS, along with significantly greater exotic bird (n=4) richness and abundance than PAR, which possessed significantly greater native bird (n=25) richness and abundance. Native birds were more abundant than exotic birds in green spaces with average noise levels < 52 dB and average NDVI > 0.5. Occupancy models indicate that green space occupancy by 50% of modeled native bird species was influenced by maximum noise levels, playing a larger role than vegetation (30%) and the urban matrix (0%). We stress the importance of developing networks of large green spaces in rapidly urbanizing regions, with abundant tree cover, surrounded by smaller urban morphology, and regulating noise levels to ensure the preservation of native bird communities in cities, particularly those of greater conservation value.
The weekend effect hypothesis predicts that weekly cycles of human activity impact animal behaviour and physiology. This hypothesis has been supported in the context of recreational activity in natural environments, but it is unknown whether it also applies to urban animals. We tested this hypothesis by comparing the sentinel (territorial vigilance), foraging and vocal behaviours of an urban‐dwelling bird, the Rufous Hornero Furnarius rufus, between weekdays and weekends (and holidays) within a university campus in central Brazil. The level of human activity (noise, traffic, and pedestrian flow) increases greatly on weekdays on this campus. We predict that the birds would perceive a greater predation risk and would need to adjust their acoustic signals in response to anthropogenic noise on weekdays. Thus, we expected that the birds would spend more time as sentinels and less time foraging, and would sing for longer periods and at a higher pitch on weekdays than at weekends. We also expected weaker duet responsiveness (answering partner‐initiated song) on noisier weekdays than at weekends, assuming that noise would disrupt signal transmission between partners. We found that birds spent slightly more time (~4%) in sentinel behaviour and less time (~2–5%) foraging on weekdays than at weekends, but these effects were small and not statistically significant. Birds were equally likely to sing solos, start duets and answer partner‐initiated duets at weekends and weekdays. Finally, phrase duration and acoustic parameters of duets were similar at weekends and weekdays. Our results provide little support for the weekend effect hypothesis, suggesting that these urban‐dwelling birds might be habituated or indifferent to periodic variation in human activity levels.
Land‐use transformation is one of the most important and pervasive ecological changes occurring across the Earth, but its long‐term effects are poorly understood. Here, we analyze the effects of urban and agriculture development on bird biodiversity and community structure over a 16‐yr study period. We found that long‐term effects of land‐use change are dependent on spatial scale and land‐use type. At the regional scale, we found that gamma diversity (total number of species observed) declined by ~10% over time. At the landscape spatial scale, we found that beta diversity (uniqueness of bird communities) increased by ~16% over time. Additionally, the average contributions of urban riparian bird communities to beta diversity were generally the highest but declined by ~26% over the study period. Contributions of urban communities to beta diversity were generally the lowest but increased by ~10% over time. At the local scale, we observed different responses for different measures of alpha diversity. For bird species richness, temporal changes varied by land use. Species richness declined 16% at sites in desert riparian areas but increased by 21% and 12% at sites in urban and agricultural areas, respectively. Species evenness declined across all land uses, with some land uses experiencing more rapid declines than others. Our analysis of species groups that shared certain traits suggests that these community‐level changes were driven by species that are small, breed onsite, and feed on insects, grains, and nectar. Collectively, our results suggest that biodiversity declines associated with land‐use change predominate at the regional and local spatial scale, and that these effects can strengthen or weaken over time. However, these changes counterintuitively led to increases in biodiversity at the landscape scale, as bird communities became more unique. This has implications for conservation and management as it shows that the effects of land‐use modification on biodiversity may be positive or negative depending on the spatial scale considered.
Towns and villages are sometimes viewed as minor, even quaint, spots, whereas this book boldly reconceptualizes these places as important dynamic environmental 'hotspots'. Multitudes of towns and villages with nearly half the world's population characterize perhaps half the global land surface. The book's pages feature ecological patterns, processes, and change, as well as human dimensions, both within towns and in strong connections and effects on surrounding agricultural land, forest land, and arid land. Towns, small to large, and villages are examined with spatial and cultural lenses. Ecological dimensions - water, soil and air systems, together with habitats, plants, wildlife and biodiversity - are highlighted. A concluding section presents concepts for making better towns and better land. From a pioneer in both landscape ecology and urban ecology, this highly international town ecology book opens an important frontier for researchers, students, professors, and professionals including environmental, town, and conservation planners.
Biodiversity monitoring and assessment across a variety of gradients, could be achieved with the aid of the ecoacoustics discipline. Acoustic monitoring approaches can provide results regarding the species richness of birds, bats, frogs and insects including cicadas ( Cicadoidea ) and katydids ( Tettigoniidae ) with results similar to the ones provided by classical ecological methods (e.g. visual point count methods). The risk of extinction of several species has led to the creation of the Natura 2000 Network in the European Union’s territory. Greece provides a number of 202 Special Protection Areas (SPA’s) and 241 Sites of Community Importance (SCI), 239 of which are considered as Special Areas of Conservation (SAC). The specific areas provide both, an opportunity for ecoacoustics practice and an opportunity for ecoacoustic research. Even though the specific field of ecology has proven to be a valuable biodiversity assessment tool, areas that provide a variety of ecoacoustic events are yet to be documented. The goal of the specific article is to highlight these special conservation areas and propose a monitoring network using the non-invasive approach of ecoacoustics. For the specific research, the Greek protected areas were visualized in order to highlight sonotopes and soundtopes worthy of future research. Finally, in order to highlight the neglected issue of background noise regarding conservation efforts, the Kalloni’s salt pans were selected as a case study area. Noise measurements and sound recordings were conducted. Furthermore, noise and sound maps were created, in order to visualize the effects of noise.
While the negative impacts of road infrastructure on faunal diversity and abundance have been extensively studied, many traffic noise studies have been conducted in the presence of confounding factors. Therefore, the extent to which traffic noise alone is responsible for impacts is not well known and a better understanding is required to inform urban planning and management decisions. We examined the impact of traffic noise on soundscape patterns at road edges in urban forests. Acoustic sensors were deployed at road and powerline edges, as well as within interior habitat, at three sites in south-east Queensland, Australia. Powerline edges were included to separate edge effects from traffic noise impacts. We used soundscape power (normalized watts per kHz) of technophony (traffic noise in the 1–2 kHz range) and biophony (animal sounds in the 3–11 kHz range) to investigate soundscape patterns. The results showed that biophony was consistently lower at road edges and was negatively correlated with traffic noise and positively correlated with distance to road edge. Technophony was higher at road edges and was found to correlate negatively with distance to road edge and positively with traffic noise. Technophony and biophony at powerline edges generally exhibited values comparable to interior habitat. These results indicate that traffic noise affects urban forest soundscape patterns at road edges in south-eastern Australia.
Studies have found that some birds use vocalizations with higher minimum frequency in noisy areas. Minimum frequency is often measured by visual inspection of spectrograms (“by-eye practice” (BEP)), which is prone to bias, e.g., if low-frequency components are masked by noise. We tested for this bias by comparing measurements of minimum frequency obtained with the BEP for the same set of red-winged blackbird vocalizations (songs and two call types “checks” and “cheers”) played back under ambient, medium, and high noise conditions using a dual playback experiment where both vocalizations and noise were introduced. We compared BEP measurements to those obtained from power spectrum analyses using a preset amplitude threshold (“threshold method” (TM)). The BEP was biased when measuring the minimum frequencies of songs and checks, which are masked by noise, but not when measuring cheers, which are higher pitched and thus not masked. Measures using the TM were not affected by noise, but this method may fail to identify the vocalizations’ lowest frequency if noise necessitates a low (i.e., conservative) threshold. Using the BEP, we also found a bias toward shorter-duration measurements for songs in increasing noise, and for checks, a bias toward increased measures of an energy distribution parameter (Freq5%), likely in correlation with increased measured minimum frequency. Measures taken from the unmasked cheers were similar regardless of the technique used. We discuss limitations of each approach and encourage the use of the TM, as studies using the BEP may lead to spurious results.
Significance statement
Noise from human activities is ubiquitous. Researchers have found that some birds vocalize at higher frequency (pitch) in noise, hypothesizing that this may improve signal detection in low-frequency noise. Noise may also hinder detection of signal components by researchers using the most common measurement technique (the BEP), which may be mistaken for increasing frequency. To examine this bias, we conducted a dual playback experiment, in which we broadcast the same vocalizations at three background noise levels. We found that BEP measures of minimum frequency increased with increasing noise even though the vocalizations did not change. We recommend the TM which yielded similar measures across noise levels, although it excluded some lower-frequency elements included by the BEP. We encourage researchers to use the TM over the BEP and to validate their methods across noise levels of interest.
Global increases in environmental noise levels arising from expansion ofhuman populations, transportation networks, and resource extraction have catalysed a recent surge of research into the effects of noise on wildlife. Synthesising a coherent understanding of the biological consequences of noise from this literature is challenging. Taxonomic groups vary in auditory capabilities.. wide range of noise sources and exposure levels occur, and many kinds of biological responses have been observed, ranging faint individual behaviours to changes in ecological conununities. Also, noise is one of several environmental effects generated by human activities, so researchers must contend with potentially confounding explanations for biological responses. Nonetheless, it is clear that noise presents diverse threats to species and ecosystems and salient patterns are emerging to help inform future natural resource-management decisions. We conducted a systematic and standardised review of the scientific literature published from 1990 to 2013 on the effects of anthropogenic noise on wildlife, including both terrestrial and aquatic studies. Research to date has concentrated predominantly On European and North American species that rely on vocal corrununication, with approximately two-thirds of the data set focussing on songbirds and marine mammals. The majority of studies documented effects from noise, including altered vocal behaviour to mitigate masking, reduced abundance in noisy habitats, changes in vigilance and foraging behaviour, and impacts on individual fitness and the structure of ecological communities. This literature survey shows that terrestrial wildlife responses begin at noise levels of approximately 40 dIlA, and 20% of papers documented impacts below 50 dBA. Our analysis highlights the utility of existing scientific information concerning, the effects of anthropogenic noise on Wikllife for predicting potential outcomes of noise exposure and implementing meaningful mitigation measures. future research directions that Would support more comprehensive predictions regarding the magnitude and severity of noise impacts include: broadening taxonomic and geographical scope, exploring interacting stressors, conducting larger-scale studies, testing mitigation approaches, standardising reporting of acoustic metrics, and assessing the biological response to noise-source removal or mitigation. The broad volume of existing information concerning the effects of anthropogenic, noise on wildlife offers a valuable resource to assist scientists, industry, and natural-resource managers in predicting potential ()incomes of noise exposure.
Even though the term “soundscape” is strictly ecological, it has been incorporated in various interdisciplinary studies. The definitions attributed to this term to date, in chronological order, reveal its ecological roots. Nevertheless, the ecological background of soundscapes did not pose as a barrier towards its expansion, but was rather beneficiary towards environmental sciences and other disciplines. These incorporations are the reason for the theoretical broadening of the term. This specific review highlights the use of an ecological term in non-ecological disciplines. Furthermore, the mapping of this extension over the years as well as the identifying any trends in the term’s use per discipline, haven’t been researched to date. In order to answer these questions, we initially assessed all publications appearing between 1969 and 2011 that incorporated the term “soundscape” in their title (about 3,200 references). Multiple and non-scientific entries were excluded from the research by filtering the results. The final dataset (979 entries) was classified regarding year of publication and scientific sub-discipline. Our results indicate “outbursts” regarding publication number in soundscape literature that could be attributed amongst other reasons, to several legislative developments concerning the assessment and management of environmental noise.
Degradation of acoustic signals during transmission presents a challenging selection pressure for animals dependent on vocal communication. Sound transmission properties differ among habitats and may drive the evolution of vocal signals in different directions. Urban habitat is expanding worldwide and an increasing number of species, including many birds, must now communicate around buildings and over concrete. Urban habitats are evolutionarily new, although to some extent they may acoustically resemble rocky habitat such as cliffs and canyons. Neither urban nor these natural habitats have been studied in any detail for the selection pressure they may exert on animal communication. Dark-eyed Juncos (Junco hyemalis) commonly inhabit montane pine forests across North America, but for about 25 years an isolated population has been successfully breeding in an urban environment in southern California. We investigated potentially divergent selection pressures on junco songs, using sound transmission experiments with artificial sound stimuli, in natural forest habitat and in this urban habitat. Transmission properties differed significantly, resulting in tails of reflected sound with gradually declining amplitude in the forest and in multiple discrete echoes in the urban environment. We expected environmental selection in urban habitat to favor shorter songs with higher frequencies and slower trill rates. Despite the presence of relatively short urban songs, there was no significant shortening overall. There were also no differences in trill rates, but we did find a significantly higher minimum frequency in the urban junco population compared to three of four forest populations. Although the pattern of song divergence was not consistent and it is difficult to draw firm conclusions from this single urban population, our transmission results suggest that echoes could be important in shaping urban birdsong.
Urban Turdus merula, in comparison with non-urban ones, show significant ecological differences. -from Authors
The effect of habitat edge and patch size on rates of nest predation depends on the predator species involved and especially how they use the landscape mosaic. Edge-related increase in predation seems to be most commonly found inside forests surrounded by farmland and was rarely found in forest mosaics. The effect in open habitat seems to be unclear, mainly because it is a more heterogeneous group of habitat edges than the other ones. Thus, a habitat edge does not necessarily generate an edge-related increase in predation pressure. However, the same type of habitat patch can have different qualities, owing to differences in the surrounding habitats. Therefore, one must also take into account the properties of neighboring habitats to understand the abundance and distribution of species in habitat patches. It is not enough to just consider the size and internal habitat quality of the patch. Even prey species that experience the landscape as a mosaic of isolated habitat patches (a divided landscape) might be influenced by predators entering from the surroundings. -from Author
Empirical evidence to assess the hypothesis that nest predation pressure influences avian assemblage composition is mostly lacking. We examined distribution of predation risk for artificial bird nests in the understory of coniferous and deciduous forests in southeastern Alaska and adjacent western Canada to determine whether habitat-specific nest predation pressure could be a factor influencing habitat selection and, in turn, breeding bird diversity. Two sizes of open-cup nests were constructed of natural materials and placed in nest sites representative of those used by local breeding bird species although, on average, artificial nests were more conspicuous than natural nests monitored in a companion study. Artificial nests were exposed to predation during early and late nesting seasons in 1993 and 1994. Principal nest predators identified using automated cameras were red squirrel (Tamiasciurus hudsonicus), Steller's Jay (Cyanocitta stelleri; Alaska only), Gray Jay (Perisoreus canadensis; Canada only), and small mammals. Systematic point-count censuses recorded significantly more red squirrels than jays in coniferous forest, and both jay species reached peak abundances at the border between coniferous and deciduous forest, relative to interior forest of both types. In repeated-measures analysis of variance, predation of artificial nests was significantly higher in coniferous than deciduous forest, and greater for large (thrush size) than for small (warbler size) nests. Nest height (shrub vs. ground) was not an important factor, due to a significant interaction with time (early vs. late nesting season). Natural and artificial nest predation losses were comparable in deciduous forest, but artificial nests were more susceptible than natural nests in coniferous forest understory. Artificial nest losses reflected the distribution of predators, especially red squirrels, and was negatively associated with breeding bird diversity in northwestern forest understory--confirming that nest predation pressure is one (of several) plausible determinants of avian habitat selection and assemblage organization.
Predation on bird eggs and nestlings on this sandplain grassland in S Maine, was positively correlated with foraging for invertebrates by striped skunks Mephitis mephitis in plots of primary skunk usage. The hypothesis that skunk predation was incidental, rather than targeted towards birds' nests, was also supported by the absence of skunk foraging behavior consistent with active nest searching, absence of a relationship between nest success and vegetative cover or promixity to a forest/grassland edge, the low density of breeding birds (<2.0 territories ha-1) on these grasslands, and the small proportion of avian material, 1.5% reported in the summer skunk diet. Although nest predation was high (58.0% overall), its unpredictability probably limits the utility of certain antipredator behaviors by birds nesting at this site. -from Authors
We quantified predation on artificial nests in Iowa roadsides and examined the relationships between nest predation and characteristics of roadsides. Transects consisting of 10 nests (five in the foreslope and five the in backslope) were set up in 136 roadsides in six watersheds in south-central Iowa. Most roadsides had herbaceous vegetation with fences (67%); fewer were wooded (18%) or had herbaceous vegetation without fences (15%). Most roads were gravel (80%), and most roadsides were adjacent to row crops (63%). Average total nest predation per transect was 23% (SE = 2), ranging from 0 to 100%. Nest predation was categorized into one of three outcomes; disappearance of eggs without disturbance to the nest bowl (39%), disappearance of eggs with disturbance to the nest bowl (17%), and broken or crushed egg shell fragments in or near the nest bowl (44%). Wooded roadsides and herbaceous roadsides with fences had significantly greater nest predation than herbaceous roadsides without fences for disappearance of eggs without disturbance to the nest bowl. Backslopes had significantly greater nest predation than foreslopes for all outcome categories except the disappearance of eggs with disturbance to the nest bowl. Wooded roadsides and herbaceous roadsides with fences along the backslope may provide cover and travel corridors for mammalian predators or elevated perches for avian predators.
Road traffic affects the natural environment in numerous ways. The most striking of these is the death
of wild animals and birds as a result of collisions with moving vehicles. In this paper the available data on bird mortality on roads are reviewed. Estimates of annual mortality for some European countries (350 000 to 27 million birds), the monthly distribution of casualties, their distribution among sex and age classes, as well as the methods used in the study of this problem are presented. The species composition of birds killed in this way is compared for several countries. In western Europe sparrows and Blackbirds are the species that most frequently die on the roads, but in Central and Eastern Europe not only sparrows but also corvids and Barn Swallows make up a high proportion of the victims. Analysis of the monthly distribution of casualties in 10 species shows this to differ between countries, probably because of the geographic variation of certain aspects of their biology (migration, breeding etc.). Several factors affecting the frequency of casualties are discussed, and some suggestions for the prevention of bird casualties are also given.
Human alteration of Earth is substantial and growing. Between one-third and one-half of the land surface has been transformed
by human action; the carbon dioxide concentration in the atmosphere has increased by nearly 30 percent since the beginning
of the Industrial Revolution; more atmospheric nitrogen is fixed by humanity than by all natural terrestrial sources combined;
more than half of all accessible surface fresh water is put to use by humanity; and about one-quarter of the bird species
on Earth have been driven to extinction. By these and other standards, it is clear that we live on a human-dominated planet.
Variable retention, or the retention of live (residual) trees within logged stands, is thought to reduce the impact of clearcutting on wildlife. However, it has been suggested that this practice may increase nest predation for songbirds nesting within these stands, resulting in an “ecological trap”. We tested this hypothesis using experimental (artificial nests) and observational (natural nests) approaches in the montane forests of the Rocky Mountains in southeastern British Columbia, Canada. In each of 2 years, we placed 720 artificial nests in 24 stands (16 logged, 8 burned by wildfire) of similar age which varied in residual tree density from 0 to 180trees/ha (residual basal area 0–19.0m3/ha). Natural nests of ground and shrub-nesting songbirds were monitored in four additional logged stands that varied in residual tree density from 8 to 64trees/ha (residual basal area 0.5–4.6m3/ha). There was no strong or consistent evidence that predation on nests of ground and shrub-nesting birds increased in association with residual tree density. Predation on artificial nests increased moderately with residual tree density in logged stands, but in only one of 2 years. In burned stands there was no relationship in either year. There was no difference in overall predation rates on artificial nests in logged and burned stands. Predation was caused mainly by birds, squirrels and small mammals, and predation by birds showed the strongest relationship with residual tree density. Predation on natural nests was less frequent than that on artificial nests, and did not increase with residual tree density. Thus, there was no indication that variable retention stands acted as ecological traps for songbirds.
There are 370 000 kilometres of roads in Great Britain, mostly bordered by a verge that is potential habitat for small mammals. The present study assessed the importance of road verges as small mammal habitat and investigated the influence of some key features on rodent abundance. Five rodent and three shrew species were live-trapped on 14 road verges in late summer 1994 and nine verges in autumn 1996 in north Cambridgeshire, UK. On average, between three and four species were captured per verge. Bank Voles Clethrionomys glareolus, Wood Mice Apodemus sylvaticus and Field Voles Microtus agrestis were the most abundant species, with mean densities of 45.5, 40.2 and 29.5 animals km(-1) in summer and 52.8, 181.9 and 47.2 animals km(-1) in autumn. Numbers varied between verges and this was significantly correlated with particular features on the verge. Bank Vole and Field Vole numbers showed a significant positive correlation with the dimensions of hedges and the width of the tall grass area, respectively. Wood Mice were also more numerous on verges with big hedges but the relationship between mouse abundance and verge structure was complex. The number of mice in 1994 was positively and significantly correlated with hedge features and with the width of the short grass sightline, whereas, in autumn 1996, they were only significantly correlated with total verge width (positive association) and ditch width (negative association).
I examined the distribution and abundance of bird species across an urban gradient, and concomitant changes in community structure, by censusing summer resident bird populations at six sites in Santa Clara County, California (all former oak woodlands). These sires represented a gradient of urban land use that ranged from relatively undisturbed to highly developed, and included a biological preserve, recreational area, golf course, residential neighborhood, office park, and business district. The composition of the bird community shifted from predominantly native species in the undisturbed area to invasive and exotic species in the business district. Species richness, Shannon diversity, and bird biomass peaked at moderately disturbed sites. One or more species reached maximal densities in each of the sites, and some species were restricted to a given site. The predevelopment bird species (assumed to be those found at the most undisturbed site) dropped out gradually as the sites became more urban. These patterns were significantly related to shifts in habitat structure that occurred along the gradient, as determined by canonical correspondence analysis (CCA) using the environmental variables of percent land covered by pavement, buildings, lawn, grasslands, and trees or shrubs. I compared each formal site to four additional sites with similar levels of development within a two-county area to verify that the bird communities at the formal study sites were representative of their land use category.
Based on more than 300 individually marked American Robins (Turdus migratorius) and Brown Thrashers (Toxostoma rufum), I tested three hypotheses to explain low return rates of birds whose nesting attempts are unsuccessful: (1) birds with low reproductive success are low-quality individuals that are more likely to suffer mortality between breeding seasons; (2) nesting failure increases reproductive effort by causing birds to renest, and this energetic stress increases the probability of mortality; and (3) birds use a 'decision rule' based on prior experience to select nesting sites, such that individuals that experience low reproductive success are more likely to move to an alternate breeding site, whereas birds that nest successfully are more likely to breed in the same site again. Birds subjected to experimental nesting failure returned at a significantly lower rate (robins 18%, thrashers 12%) than birds that nested successfully (robins 44%, thrashers 29%). Birds that nested more than once in a season returned at rates (robins 43%, thrashers 21%) indistinguishable from birds that nested only once in a season (robins 36%, thrashers 23%). These results, as well as supplementary data, were inconsistent with hypotheses 1 and 2 and consistent with hypothesis 3. This study provides strong evidence that low return rates result from dispersal in response to nesting failure.
Defines urbanisation as those areas with a population of >620 individuals km-2. Characteristic urban structure and the range of components are also described. Urbanisation is seen as presenting a complex environmental gradient. Landscape ecology is discussed. By studying urban gradients humans can be seen as integral and critical components of ecological systems. -S.J.Yates
The effect of traffic noise on the breeding density of 20 passerine species was examined over a 2-year period in three different road types passing through pasture-woodlands in western-central Spain. No statistically significant differences were observed during the 2 years studied. An average of 19.6 birds/10 ha was recorded for the low-traffic road (LT), 21.7 birds/10 ha for the medium-traffic road (MT) and 19.1 birds/10 ha for the high-traffic road (HT). A total of 11 species (55%) did not show any statistically significant differences in breeding density among the different types of roads. By contrast, other species, such as the Blackbird, the Iberian Shrike and the Linnet, did point to differences between the MT and HT roads. House and Rock Sparrows, as well as the Corn Bunting, showed higher breeding densities near the HT road. The opposite effect was observed for the Wheatear, the Iberian chiffchaff and the Woodlark, for which high breeding densities were recorded in the vicinity of the LT road. Our results suggest that traffic noise constitutes a serious problem for at least 15% of the breeding bird community.
We compared the avifauna in two cities, Quebec (Canada) and Rennes (France), in order to define general responses of wildlife in an urban ecosystem. These cities have a similar urban structure that permits investigation along an urbanization gradient from downtown to rural residential areas. However, they are in opposite temperate climate and imbedded in a forested and an agricultural landscape, respectively. Plots ranging from 10 to 20 ha were surveyed in winter and spring by recording all birds seen or heard. Most plots could be located along a gradient according to proportions of vegetated open space. Both the Shannon-Wiener and Simpson indices of diversity indicated a pattern of increasing diversity from most to least urbanized areas in spring. Winter species diversity and richness was low in Quebec compared to Rennes, reflecting the much harsher winter conditions in Quebec. Breeding densities of House Sparrows (Passer domesticus) and European Starlings (Sturnus vulgaris) were quite similar in Quebec and Rennes, as were densities of European Blackbirds (Turdus merula) and its ecological equivalent in Quebec, the American Robin (Turdus migratorius). The type of surrounding landscape can not explain the Variation of species numbers within the city. If we examine the urban environment as a new ecological system rather than a degraded environment, we can regroup birds in two major species groups: the omnivorous species adapted to the urban environment and its particular food resources such as garbage and the species that find, in the urban environment, resources which they normally exploit in their usual habitat.
Conservation biology and comparative psychology rarely intersect, in part because conservation biology typically emphasizes populations whereas comparative psychology concentrates on individual organisms. However, both fields could benefit from their integration. Conservation biology can profit from an enhanced understanding of individual-level impacts of habitat alteration and the resulting implications for conservation mitigation strategies. Comparative psychology can gain from increased attention to the mechanisms of adjustment used by organisms to "in vivo experiments" created by anthropogenic change. In this paper, we describe a conceptual framework useful for applying our understanding of animal communication to conservation biology. We then review studies of animal communication with conservation implications, and report our own preliminary work that demonstrates our framework in action. Copyright Information:
Development pressures in rural mountainous areas of the United States hold crucial implications for water quality. Especially important arc changes in the extent and pattern of various land uses. We examine how position along an urban-rural gradient affects landscape patterns in a southern Appalachian watershed, first by testing for the effect of distance from an urban center on land-cover change probabilities and then simulating the implied development of a landscape at regular distance intervals. By simulating a common hypothetical landscape we control for variable landscape conditions and define how land development might proceed in the future. Results indicate that position along the urban- rural gradient has a significant effect on land-cover changes on private lands but not on public lands. Furthermore, position along the gradient has a compounding effect on Jand- cover changes through interactions with other variables such as slope. Simulation results indicate that these differences in land-cover changes would give rise to unique "landscape signatures" along the urban-rural gradient. By examining a development sequence, we identify patterns of change that may be most significant for water quality. Two locations along the urban-rural gradient may hold disproportionate influence over water quality in the future: (1) at the most remote portion of the landscape and (2) at the outer envelope of urban expansion. These findings demonstrate how landscape simulation approaches can be used to identify where and how land use decisions may have critical influence over environmental quality, thereby focusing both future research and monitoring efforts and watershed protection measures.
We assessed the role of park size, habitat structure, human disturbance (pedestrian rate and ambient noise), and the number of conspecifics in the distribution, spacing, and singing behavior of male house finches (Carpodacus mexicanus) in urban parks in southern Los Angeles County and north Orange County, California. We found that the probability of house finch males occupying urban parks increased with park size and tree structure (total tree cover, tree height, and the number of stems 30 to 50 centimeters in diameter)—two features that may increase the availability of suitable nesting substrates. Nearest neighbor distance between singing males increased with denser vegetation structure (e.g., number of stems), probably because of better nes ting and foraging resources, or greater availability of protective cover, which would reduce aggregation. Males increased their singing rates in the most exposed parts of their perches (upper and outer portions). They also raised the low frequency of their songs to reduce the masking effects of high ambient noise levels. However, the number of notes per song decreased with ambient noise, and since females are attracted to long songs, this could decrease mating opportunities. Our results point out some of the mechanisms house finch males use to increase their breeding success in urbanized areas and suggest that this success may vary depending on the specific spatial location of nesting areas within a city.
Depredation of artificial ground nests was examined in tropical savanna in northern Australia to assess potential predation pressures on nests of the partridge pigeon (Geophaps smithii), a declining tropical granivore. Predation rates were examined at two sites, Kakadu National Park (which supported a relatively high density of partridge pigeons) and Berry Springs (which had greater habitat fragmentation and comparatively low partridge pigeon density). The effects of distance from road, understorey structure, topography and nest-microsite concealment on nest predation rates were examined. Artificial-nest predation rates were greater at 150 m from roads than <1 m from the roadside. Predation rates did not vary with understorey structure, topography, or level of nest concealment. There was marked variation between sites, with predation levels at Kakadu more than double those recorded for Berry Springs. Discerning predator identity, or even the size of a predator, from marks left in clay eggs proved difficult and was possible for ~35% of predation events. Of these, 42% of predation events involved predators of a size we considered too small to take a natural partridge pigeon nest. We suggest that extrapolation from artificial to natural ground-nest predation rates be undertaken with caution for landscapes such as Australia’s tropical savanna, which supports a high diversity and abundance of small potential predators of artificial nests. There was no evidence of predation by birds, and the methodology proved inadequate for identifying predation by feral cats (Felis catus).
Dans les environnements urbains, les bruits d'origine anthropique pourraient masquer les chants d'oiseaux, particulièrement les notes émises à basses fréquences (1–2 kHz). Les oiseaux qui vivent en milieux urbains pourraient modifier leur chants, particulièrement les portions à basse fréquence, pour minimiser le masquage par les bruits d'origine anthropique. De telles modifications ont été observées chez Parus major aux Pays-Bas, ainsi que chez certains mammifères. Nous avons étudié Melospiza melodia, qui est une espèce commune dans les environnements urbains et ruraux, un peu partout en Amérique du Nord. Nous avons enregistré les chants de 28 mâles en liberté à Portland, en Orégon. Nous avons également mesuré l'amplitude et le spectre des bruits ambiants sur des lieux de chants. Les Melospiza melodia qui chantaient aux sites les plus bruyants montraient des notes basses de plus haute fréquence et avaient relativement moins d'énergie (amplitude) dans la gamme des basses fréquences de leurs chants (1–4 kHz), où la plupart des bruits d'origine anthropique ont lieu. Bien que le (ou les) mécanisme(s) qui est (sont) à l'origine de cette corrélation est (sont) encore indéterminé(s), la correspondance observée entre les chants et les bruits pourrait résulter d'une plasticité comportementale. Nous discutons dans l'article des explications qui concernent ces patrons et de la façon de les tester.
In order to understand the effect of urban development on the functioning of forest ecosystems, during the past decade we have been studying red oak stands located on similar soil along an urban-rural gradient running from New York City ro rural Litchfield County, Connecticut. This paper summarizes the results of this work. Field measurements, controlled laboratory experiments, and reciprocal transplants documented soil pollution, soil hydrophobicity, litter decomposition rates, total soil carbon, potential nitrogen mineralization, nitrification, fungal biomass, and earthworm populations in forests along the 140 × 20 km study transect. The results revealed a complex urban-rural environmental gradient. The urban forests exhibit unique ecosystem structure and function in relation to the suburban and rural forest stands these are likely linked to stresses of the urban environment such as air pollution, which has also resulted in elevated levels of heavy metals in the soil, the positive effects of the heat island phenomenon, and the presence of earthworms. The data suggest a working model to guide mechanistic work on the ecology of forests along urban-to-rural gradients, and for comparison of different metropolitan areas.
Urbanization - the anthropogenic conversion of natural ecosystems into human-dominated ecosystems - has occurred on global scales. The human-dominated landscape presents particular challenges to researchers because the effects of urbanization on ecological processes are not well understood. We investigated the influence of urbanization on predation by conducting an artificial nest experiment along an urban gradient of six sites ranging from natural to urbanized ecosystems. Previous hypotheses suggest that predation pressures in urban environments will either 1) increase because of the high abundance of exotic species which act as predators or 2) decrease due to the lack of natural predators. To determine relative predation pressures among sites along the urban gradient, we monitored the fates of 16 artificial avian nests at each of the six sites for a total of 96 nests in each year (1996, 1997). We analyzed the dependency of nest fate (depredated or undisturbed) on intensity of urbanization (sites along the urban gradient), nest height (ground, above-ground), and year using loglinear models. The frequency of nest predation was strongly dependent on site along the urban gradient, indicating that urbanization intensity was an important determinant of nest fate. Predation pressure exhibited an overall decline from natural to urban sites in both years, suggesting that urban environments have low predation pressures relative to natural areas. The predatory relaxation in urban environments may partially explain the greater abundance of some species in urban environments, particularly urban exploiters such as european starlings Sturnis vulgaris, house sparrows Passer domesticus, and rock doves Columba livia.
Predation by carrion crows Corvus c. corone of Fulica atra eggs was studied in the Camargue. Observations from an elevated platform revealed the degree of egg predation without human disturbance. This was 18% of the eggs laid (c1 crow/10 ha. 10 coot pairs). Nest success was highest on marsh with dense Phragmites australis reeds, followed by the marsh with Tamarix trees which coots used for nesting and then the marsh with open reedbeds of Typha and Scirpus. Within a marsh or vegetation unit nest cover did not affect the changes of predation. Although regular nest visits by humans increased predation of clutches, this was significant only for daily nest visits where crows specialised on egg predation. Crows found artificial clutches within 5 hr and developed a specific searching image for them in heavily disturbed marshes. Thus, frequent nest visits may influence the behaviour of individual crows to such an extent that they prevent reliable research on the breeding ecology of the coot population. -from Author
Abstract A huge road network with vehicles ramifies across the land, representing a surprising frontier of ecology. Species-rich roadsides are conduits for few species. Roadkills are a premier mortality source, yet except for local spots, rates rarely limit population size. Road avoidance, especially due to traffic noise, has a greater ecological impact. The still-more-important barrier effect subdivides populations, with demographic and probably genetic consequences. Road networks crossing landscapes cause local hydrologic and erosion effects, whereas stream networks and distant valleys receive major peak-flow and sediment impacts. Chemical effects mainly occur near roads. Road networks interrupt horizontal ecological flows, alter landscape spatial pattern, and therefore inhibit important interior species. Thus, road density and network structure are informative landscape ecology assays. Australia has huge road-reserve networks of native vegetation, whereas the Dutch have tunnels and overpasses perforating road barriers to enhance ecological flows. Based on road-effect zones, an estimated 15–20% of the United States is ecologically impacted by roads.
Neotropical migrant birds are declining within many forest communities in North America and concern exists regarding the impact of forest fragmentation on their breeding success, particularly with respect to nest predation. We studied predation on artificial ground nests in large forest blocks to provide information for comparison with forest fragments and to determine the importance of predator community and vegetation. From May through August 1991, we distributed 320 artificial ground nests over 8 4-ha study plots and measured 12 vegetational variables at these nests. We used remote-triggered cameras to identify predators. Nest predation rates varied from 5 to 40% among study plots. Vertical vegetational density, horizontal log density, and percent herbaceous, rock, soil, and litter cover were different (P < 0.05) between successful and unsuccessful nests. A diverse predator community, including small mammals, is responsible for loss of artificial nests and predation rates are not solely a function of forest size.
Because artificial nests can facilitate controlled experiments of nest success, we used them to assess whether human visitation, nest density, vegetation structure, and proximity to habitat edge could affect depredation of duck nests on Yukon Flats National Wildlife Refuge, Alaska. More (P < 0.01) nests in a plot visited daily (100%) were depredated than those in plots visited at intervals of 7 (40%), 14 (35%), or 28 days (45%). More (P < 0.01) nests were depredated in a plot with 10 nests/ha (95%) than nests in a plot of a lower density (2/ha; 40%). Vegetation height, vegetation density, distance to a wetland, distance to forest edge, or distance to the nearest ecotone did not differ (P > 0.05) between depredated and undisturbed nests. We suggest that daily visitation of duck nests increases depredation, but longer intervals, typical of most nest studies, do not. High nesting densities, which could occur when flooding limits nesting habitat, may result in higher depredation rates.
1. Relationships between grizzly bears, habitat, and roads were investigated between 1990 and 1994 in the Swan Mountains, Montana. Relationships were examined at three levels of resource selection. 2. Differences existed between habitat and road features within, and those outside, the multi-year composite female grizzly bear home range. Using logistic regression, large resource selection probability functions were obtained for the subalpine zone within multiple-use lands having no roads. Selection probability was zero for private lands and declined as total road density increased. 3. Within seasonal ranges, most grizzly bears favoured low temperate and temperate elevation zones over the subalpine zone during all seasons. Relative to forested habitats, avalanche chutes were positively selected for during all seasons, but especially in spring. Shrub lands and cutting units were important to most bears during summer and autumn. Grizzly bears were more closely associated with higher total road densities during spring than during other seasons. When in low temperate habitats, most bears used habitats with lower total road density than occurred randomly. 4. Seasonal use by grizzly bears of areas within a 0.5 km buffer surrounding roads was evaluated. Most grizzly bears exhibited either neutral or positive selection for buffers surrounding closed roads and roads receiving <10 vehicles per day but avoided buffers surrounding roads having >10 vehicles per day. 5. Between 1988 and 1994, eight grizzly bears were killed by humans. These deaths were directly influenced by road access and unnatural food sources. These deaths, in addition to natural mortality, were too great to promote local population growth.
Despite intensive management on many grassland areas, nest loss to predators continues to result in low nest-survival rates. Management efforts are complicated by complex relationships among habitat, predators, and prey resources. We monitored the fates of artificial nests (908 in 1993, 827 in 1994) on Conservation Reserve Program (CRP) plots from April to July to test effects of prey supplementation, vegetation density, and time (month) on nest survival in agricultural and range landscapes in northwest Texas. Supplemental prey had the greatest effect on artificial nest survival and increased nest survival in both sparse and dense vegetation. Prey supplementation may be useful when used in conjunction with habitat management for dense nesting cover or in areas that already have dense vegetation. Nest survival was highest early in the nesting season, emphasizing the importance of available nesting cover during this period. Although least important, dense vegetation increased artificial nest survival. When evaluating management options, managers should consider logistical and economic costs of using supplemental prey, as well as potential effects on predator population dynamics.
Many recent studies have addressed the effects of patch size and isolation on bird communities in highly fragmented landscapes, but the importance of landscape composition in more forested landscapes remains poorly understood. The objectives of our study were (1) to determine the effects of two structurally and temporally distinct disturbance types (agriculture and silviculture) and extent of disturbance (percentage of disturbance within 1.0 km) on avian community structure within forested landscapes, and (2) to investigate underlying mechanisms responsible for associations between landscape composition and avian communities. Differences in microhabitat, microclimate, and nesting success among landscapes were examined as possible mechanisms. Breeding bird communities in central Pennsylvania (USA) were surveyed twice per year during 1997-1999 at 34 sites within contiguous mature forest, which represented a range of disturbance extent (4-59% nonforest cover within 1.0 km). Each site was in a forested landscape containing predominantly agricultural or silvicultural disturbances (n = 17 each). Our results indicate that type of disturbance within landscapes influenced bird community composition and relative abundance more than extent of disturbance. Compared to forests within landscapes disturbed by silviculture, forests within landscapes disturbed by agriculture, irrespective of the extent of disturbance, had fewer forest-associated species, long-distance migrants, forest-canopy and forest-understory-nesting species, and greater numbers of edge-associated species, including avian nest predators and Brown-headed Cowbirds (Molothrus ater). Fewer species and guilds were associated with the extent of disturbance within a landscape or interactions between disturbance type and extent. Abundances of edge-associated species, residents, and forest-canopy nesters increased with increasing amounts of disturbance within forested landscapes. Local variation in microhabitat and microclimate among landscapes did not explain observed differences in avian community structure. However, nesting success was greater and numbers of some avian and small mammalian nest predators were lower in stands within forested landscapes disturbed by silviculture than in forested landscapes disturbed by agriculture. Nesting success was not associated with the extent of a given disturbance type within landscapes. These results demonstrate that, even within forested landscapes, the types of disturbance can influence avian community structure and, thus, should be considered in conservation and forest management plans. In particular, agricultural disturbances within forested landscapes seemed to negatively affect bird communities in adjacent forests more than silvicultural disturbances. Both species richness and abundance of forest-associated species were greater on sites with higher levels of nesting success. Thus, differences in nesting success resulting from altered interactions between nest predators and nesting birds may be an important underlying mechanism of avian community structure and organization at the landscape scale.
The full song of the Blackbird was analysed quantitatively by means of sonagraph, level recorder and computer. Species-specific limits of variation are given for a number of song parameters. Some of these parameters vary between individuals, others vary within individuals in two situations, viz. dawn song with heavy stimulation from rivals and evening song with weak stimulation from rivals. The parameters and the differences between the variations of the parameters all seem to be within the range of auditory perception of oscines. It is therefore hypothesized that parameters varying within species-specific limits have a potential for conveying a message about the species, and that parameters varying within these limits with the individual or the situation have an additional potential for conveying individual or behavioural messages, respectively. Blackbird song was also studied with respect to adaptations for acoustic communication. Selection has favoured the evolution of a functionally divalent signal, the motif parts being adapted for long-range communication and the twitter parts for short-range communication.
Wildlife biologists historically considered the edge between adjacent habitat types highly productive and beneficial to wildlife. A current dogma is that edges adversely affect a wide range of avian species by increasing depredation and parasitism rates of nests. I critically evaluated existing empirical evidence to test whether there was a gradation in nest success as a function of distance from an edge. Researchers investigating this question have been inconsistent in their experimental designs, making generalizations about edge-effect patterns difficult. The majority of studies I examined found nest success varied near edges, with both depredation rates (10 of 14 artificial nest studies, and 4 of 7 natural nest studies) and parasitism rates (3 of 5 studies) increasing near edges. In addition, there was apositive relationship between nest success and patch size (8 of 8 studies). The most conclusive studies suggest that edge effects usually occur within 50 m of an edge, whereas studies proposing that increased depredation rates extend farther than 50 m from an edge are less convincing. Prior research has probably focused on distances too far from an edge to detect threshold values, and future research should emphasize smaller scales. 100–200 m from an edge at 20–25 m increments. Researchers often use relatively arbitrary habitat characteristics to define an edge. Therefore, I propose that only openings in the forest canopy with a diameter three times or more the height of the adjacent trees should be included in edge analyses. This review suggests that fragmentation of eastern North American temperate forests could lead to increased nest predation and parasitism, and there is need to determine if similar processes occur in other forested regions of North America.
Roads may effect animal communities in various ways. One such way is ‘di sturbance’, i.e. emission of stimuli to which animals may respond by avoiding the vicinity of the road. The extent, intensity and mechanism of this effect is almost entirely unknown. Veen (1973), studying the bird species lapwing Vanellus vanellus, black-tailed godwit Limosa limosa, oystercatcher Haematopus ostralegus, redshank Tringa totanus and ruff Philomachus pugnax in open grassland areas, found disturbance over surprisingly long distances, ranging from 500–600 m for a quiet rural road to 1600–1800m for a busy highway. However, his approach has met with serious methodological criticism.The validity of Veen's conclusions was tested by critically reanalysing bird distribution in one of his study plots. It is inferred that his conclusions do hold for the lapwing, the godwit and possibly the redshank, though not for the oystercatcher. An additional field study in four areas yielded similar results, with comparable disturbance distances. The total population loss over this distance may amount to 60%. Rough indications were obtained that the distance-density graph is a logistic one, while the relation between traffic volume and total population loss is possibly logarithmic. In addition confirmation was obtained of the general impression that, apart from roads, disturbance may also be caused by farms, other buildings and plantations, suggesting that disturbance caused by a road is not easily eliminated by planting trees alongside.It is recommended that extra care be taken in planning new roads, while impact statements concerning roads which disregard disturbance and other long-distance effects on the fauna should be rejected.
Many studies have compared songbird nesting success between forest edge and interior, but few have addressed potential factors underlying variation in nest predation pressure in relation to edge. We examined the relative abundance and species richness of songbird nest predators and the abundance of Brown-headed Cowbirds (Molothrus ater) in forest edge and interior within a fragmented, agricultural landscape in central Missouri, USA. Avian predators and cowbirds were more abundant in forest edges. There were no differences in small- or medium-sized mammalian predator abundance between edge and interior. Almost twice as many snakes were captured in edge as in interior. Predator species richness was significantly higher in forest edge. Forest vegetation structure was very similar between edge and interior, suggesting that differences in predator abundance and species richness were not driven by variation in habitat structure. Nest predator distribution in relation to habitat edge may therefore depend on factors at larger spatial scales, such as landscape context. We suggest that in areas fragmented by agriculture, nest predator assemblages in forest edges may differ from those in forest interior. Edges may attract a greater number of predator species, and some nest predators may be more abundant near the edges of forest patches, although the trend does not apply across all predator taxa. Generalizations about nest predators and edges should thus be made with caution, and conservation plans should consider the composition of local nest predator assemblages in order to predict potential impacts on nesting birds in edge habitat.
The effect of visits to nests of open-nesting passerines was investigated over two years using a randomized sampling design; the only such study ever undertaken in the UK. There was no overall effect of nest visiting on nesting success (the analysis had a power of 85% to detect a difference of 10% in success rates between control and visited nests). However, although thrushes and insectivores appeared to be beneficially affected by nest visiting, finches were detrimentally affected by nest visiting in one of the years. The effect of nest visiting did not differ between habitat, categorized into farmland, woodland and garden. The degree of exposure of the nest had no effect on nesting success but increases in the degree of disturbance made to a nest's surroundings paradoxically appeared to increase nesting success. A brief review of studies undertaken outside the UK also reveals little evidence for any effect of nest visiting on passerine nest success.
We analysed nest site selection in two shrub-steppe larks, the lesser short-toed larkCalandrella rufescensand the Thekla larkGalerida theklae. Both species nest on the ground next to a bush preferably facing north or north-east. Nestling growth and fledging weight are greater when the nest faces these directions. Both species prefer to nest next to camephytes with little foliage, and the lesser short-toed lark chooses sites with high visibility. We conclude that sunlight and nest predation are fundamental selective pressures determining nest microhabitat selection in larks in semi-arid areas.
Food plots are often used to enhance habitat for game species within forested systems, but food plots also create edge within the forested matrix that may attract nest predators. Because little information exists regarding how food plots affect nest predation, we examined predation rates on artificial nests placed in 30 food plots (0.70–13.0ha). We determined that four spatial variables and one temporal variable were important predictors of predator use of food plots. Predators used forested edges more intensively than fallow strips within food plots and small food plots with short perimeters more intensively than large food plots with long perimeters. As food plots became more irregularly shaped, intensity of predator use increased. Last, predators used food plots more intensively during the early nesting season (May) than during the later nesting season (July). Because many bird species nest along food plot/forest ecotones or in native vegetation within periodically disturbed sites, managers should consider food plot designs that reduce encounter rates between nesting birds and their predators.
Traffic noise is known to have a negative impact on bird populations in general, but little is known about the mechanisms by which sound pollution affects bird communities. However, a knowledge of these mechanisms is imperative if we want to account for the differences in susceptibility to traffic noise that exist between species, and may thus be critical for conservation action. To address this issue, population assessments were carried out in a contiguous area of oak-beech forest at differing distances from a much frequented motorway to determine the road effect on the whole bird community. As expected, species richness and diversity decreased towards the motorway, and bird abundance was significantly lower along the motorway than in the control area. However, a few species defied the negative impact of the motorway. The songs of the more abundant passerines were analysed with regard to three frequency parameters to determine whether or not a relationship exists between the song pitch of a species and its sensitivity to noise pollution. A significant relationship was found between dominant frequency and decline in abundance towards the motorway, which indicates that having a higher-pitched song with frequencies well above those of traffic noise makes a bird less susceptible to noise pollution. These results suggest that acoustic masking is one of the mechanisms by which traffic noise negatively affects passerine density along roads.
In 23 drainages in high elevation (2300 m) forest in central Arizona, variation in bird species numbers was compared to variation in area and habitat structure among drainages. Birds were grouped into foraging (bark, understory foliage, canopy foliage, aerial) and nesting (cavity, understory foliage, canopy foliage) guilds based on heights and substrates used. Numbers of species increased with area for all guilds, but species-area slopes differed among nesting guilds. Variation in numbers of species among drainages was positively correlated with variation in the density of foraging and nesting substrates, but correlations were greater when based on nesting than foraging heights and substrates. Results are consistent with a prediction that birds are selecting habitat sites based in part on the availability of nest sites that minimize risk of nest predation, and that these nest sites increase with density of foliage at nest height. Results are also consistent with a hypothesis that availability of suitable nest sites is one of the bases for the relationship between species numbers and foliage density for foliage-nesting species. Multiple activities (foraging and nesting) can allow multiple processes to act simultaneously. -from Author
Predation on nests has been suggested as an important factor limiting nest success of ground-nesting birds in habitat fragments and along habitat edges. We examined predation rates on artificial ground nests (n = 540) in relation to prairie fragment size and proximity to woody cover in 15 remnant, tallgrass prairies (4-571 ha) in southwestern Missouri. Artificial nests in prairies <15 ha (37.0% predation rate) were depredated more than those in larger prairies (13.9%; P < 0.001). Artificial nests <60 m from woody cover (28.7% predation rate) were less successful than were nests farther away (7.9%; P < 0.001). Proximity to woody cover had more influence on artificial-nest success than did tract size when both variates were incorporated in multiple logistic regression and log-linear models. The potential effects of prairie size and woody vegetation on success of ground-nesting birds should be considered in decisions regarding acquisition and management of prairie habitats.
Artificial nests are commonly used to evaluate predation, but the assumption that this method mimics predation on natural nests has seldom been tested. Natural and artificial nests of eastern yellow robins (Eopsaltria australis) were monitored in four, 55-ha plots over two breeding seasons. Overall, daily survival rates were higher (P<0.001) for natural (95%/day) than for artificial nests (88%/day). Among plots, daily survival rates for the two types of nests were not correlated with one another (P=0.72) indicating that the spatial pattern of predation on artificial nests did not mimic that for natural nests. Seasonal variation was evident for natural nests in one year, when they were more successful at the beginning and end of the breeding season. No seasonal patterns were observed for artificial nests in either year. Neither natural nor artificial nests showed annual variation in predation. Previous researchers concluded that large birds were important predators on robin nests. In this study, predation by large birds on artificial nests was positively correlated with the numbers of large birds counted on the plots (P=0.04). However, large birds depredated only 16% of artificial nests. Daily survival rates for artificial nests were recalculated using predation by large birds only. These rates were compared with natural nests, but there was still no correspondence in the spatial and temporal patterns of predation for the two types of nests. These results suggest that inferences about predation on natural nests based on artificial nest studies should be avoided.
ABSTRACT Degradation of acoustic signals during transmission presents a challenging selection pressure for animals dependent on vocal communication. Sound transmission properties differ among habitats and may drive the evolution of vocal signals in different directions. Urban habitat is expanding worldwide and an increasing number of species, including many birds, must now communicate around buildings and over concrete. Urban habitats are evolutionarily new, although to some extent they may acoustically resemble rocky habitat such as cliffs and canyons. Neither urban nor these natural habitats have been studied in any detail for the selection pressure they may exert on animal communication. Dark-eyed Juncos (Junco hyemalis) commonly inhabit montane pine forests across North America, but for about 25 years an isolated population has been successfully breeding in an urban environment in southern California. We investigated potentially divergent selection pressures on junco songs, using sound transmission experiments with artificial sound stimuli, in natural forest habitat and in this urban habitat. Transmission properties differed significantly, resulting in tails of reflected sound with gradually declining amplitude in the forest and in multiple discrete echoes in the urban environment. We expected environmental selection in urban habitat to favor shorter songs with higher frequencies and slower trill rates. Despite the presence of relatively short urban songs, there was no significant shortening overall. There were also no differences in trill rates, but we did find a significantly higher minimum frequency in the urban junco population compared to three of four forest populations. Although the pattern of song divergence was not consistent and it is difficult to draw firm conclusions from this single urban population, our transmission results suggest that echoes could be important in shaping urban birdsong.
Urbanization - the anthropogenic conversion of natural ecosystems into human-dominated ecosystems - has occurred on global scales. The human-dominated landscape presents particular challenges to researchers because the effects of urbanization on ecological processes are not well understood. We investigated the influence of urbanization on predation by conducting an artificial nest experiment along an urban gradient of six sites ranging from natural to urbanized ecosystems. Previous hypotheses suggest that predation pressures in urban environments will either 1) increase because of the high abundance of exotic species which act as predators or 2) decrease due to the lack of natural predators. To determine relative predation pressures among sites along the urban gradient, we monitored the fates of 16 artificial avian nests at each of the six sites for a total of 96 nests in each year (1996, 1997). We analyzed the dependency of nest fate (depredated or undisturbed) on intensity of urbanization (sites along the urban gradient), nest height (ground, above-ground), and year using loglinear models. The frequency of nest predation was strongly dependent on site along the urban gradient, indicating that urbanization intensity was an important determinant of nest fate. Predation pressure exhibited an overall decline from natural to urban sites in both years, suggesting that urban environments have low predation pressures relative to natural areas. The predatory relaxation in urban environments may partially explain the greater abundance of some species in urban environments, particularly urban exploiters such as european starlings Sturnis vulgaris. house sparrows Passer domesticus. and rock doves Columba livia.
The development and the continual expansion of urban areas have not only destroyed natural habitats, but also have drastically changed the environmental and ecological conditions of these areas. Consequently, species that have settled in these new man-made ecosystems are exposed to considerable alternations in environmental conditions compared to their ‘wild’ conspecifics. To understand the impact of human-induced environmental changes on life history events such as reproduction, we compared the timing of the reproductive season and its underlying endocrine control in free-living European blackbirds Turdus merula inhabiting urban and nearby forest areas. Body mass, fat score, gonadal size, luteinizing hormone (LH), testosterone (T), and estradiol (E2) were measured. Urban blackbirds developed their gonads approximately three weeks earlier than forest birds, whereas the timing of gonadal regression did not differ. There are several factors (e.g. artificial light, temperature, food availability, and social cues) which may have caused the differences in the temporal organization of gonadal growth between the urban and forest-living populations. The advanced gonadal development of urban blackbirds did not coincide with an earlier secretion of reproductive hormones. In contrast, urban males had lower plasma LH and T levels during testicular growth than forest males. Differences in social interactions and environmental conditions may explain the contrast of gonadal development and the timing of hormone secretion between urban and forest blackbirds.
Urban areas occupy a large and growing proportion of the earth. Such sites exhibit distinctive characteristics relative to adjacent rural habitats, and many species have colonised and now successfully exploit urban habitats. The change in selection pressures as a result of urbanisation has led to trait divergence in some urban populations relative to their rural counterparts, but studies have generally been local in scale and the generality of differentiation thus remains unknown. The European blackbird Turdus merula is one of the commonest urban bird species in the Western Palearctic, but populations vary substantially in the length of time they have been urbanised. Here we investigate patterns of morphological variation in European blackbirds occupying 11 paired urban and rural habitats across much of the urbanised range of this species and spanning 25° of latitude. First, we assessed the extent to which urban and rural blackbirds are differentiated morphologically and the consistency of any differentiation across the range. Paired urban and rural Blackbird populations frequently exhibited significant morphological differences, but the magnitude and direction of differentiation was site dependent. We then investigated whether the nature of latitudinal gradients in body-size differed between urban and rural populations, as predicted by differences in the climatic regimes of urban and rural areas. Blackbird body-size exhibited strong latitudinal gradients, but their form did not differ significantly between urban and rural habitats. The latitudinal gradient in body size may be a consequence of Seebohm's rule, that more migratory populations occurring at high latitudes have longer wings. We conclude that while there can be substantial morphological variation between adjacent urban and rural bird populations, such differentiation may not apply across a species’ range. Locality specific differentiation of urban and rural blackbirds may arise if the selection pressures acting on blackbird morphology vary in an inconsistent manner between urban and rural habitats. Alternatively, phenotypic divergence could arise in a stochastic manner depending on the morphological traits of colonists, through founder effects.
The contribution of roads to forest fragmentation has not been adequately analyzed. We quantified fragmentation due to roads in a 30,213-ha section of the Medicine Bow-Routt National Forest in sout heastern Wyoming with several indices of landscape structure using a geographic information system. The number of patches, mean patch area, mean interior area, mean area of edge influence, mean patch perimeter, total perimeter, and mean patch shape identified patch- and edge-related landscape changes. Shannon-Wiener diversity, dominance, contagion, contrast, and angular second moment indicated effects on landscape diversity and texture. Roads added to forest fragmentation more than clearcuts by dissecting large patches into smaller pieces and by converting forest interior habitat into edge habitat. Edge habitat created by roads was 1.54–1.98 times the edge habitat created by clearcuts. The total landscape area affected by clearcuts and roads was 2.5–3.5 times the actual area occupied by these disturbances. Fragmentation due to roads could be minimized if road construction is minimized or rerouted so that its fragmentation effects are reduced. Geographic information system technology can be used to quantify the potential fragmentation effects of individual roads and the cumulative effects of a road network on landscape structure.