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Territory regulation, tenure, and migration in Rufous Hummingbirds
Canadian Journal of Zoology
Abstract
Postbreeding migrant rufous hummingbirds (Selasphorus rufus) establish feeding territories in alpine meadows. An inverse hyperbolic relationship between territory size and flower density indicates that territory size is regulated to maintain food supply: individual hummingbirds make daily adjustments in their territories. These adjustments maintain food supplies from day lo day and improve them over what they would be if no adjustments were made. The ability of individuals to maintain territory quality, however, and the length of time they remain in the meadows, is affected by their age and sex and by the level of competition for food by conspecifics. Territoriality, therefore, must be considered in relation to factors operating beyond the local food environment, both in terms of effects on and effects of the short-term dynamics of energy regulation. This has important implications for hummingbird migration.
... Selasphorus rufus es el ave que recorre mayor distancia en proporción a su tamaño corporal (9.5cm, 3.4g), ya que de sus sitos de reproducción en el sur de Alaska a el centro de México donde migra en invierno recorre 4320 Km por lo cual requiere lugares donde reaprovisionarse de energía en los diferentes habitats de su ruta migratoria . Por lo tanto, se ha postulado que para el colibrí Rufo la migración consiste en una serie de vuelos puntuados entre "paradas" de aproximadamente 1-2 semanas para reconstruir almacenes de lípidos, reaprovisionándose de combustible Gass 1979;Heinemann 1992). En estos lugares de reabastecimiento existe una ganancia de peso corporal de entre 0.23 y 0.30 gramos por día, lo que representa cerca del 10% de su masa total (Carpenterand & Hixon 1988). ...
... La ruta migratoria de S. rufus se encuentra relacionada con la fenología de floración de diversas plantas, siguiendo las áreas con la mayor abundancia de flores abiertas (Healy & Calder 2006). La llegada de esta especie a los sitios de reabastecimiento coincide con la floración de las plantas en el lugar, en donde establece territorios de alimentación que son defendidos contra especies residentes y migratorias (Gass 1979;Heinemann 1992;. Calder (1995) postuló que los colibríes migratorios pueden llegar justo antes del pico de floración el cual les provee de un suplemento abundante de néctar. ...
... Esto podría apoyar la teoría de que El Palmito es una zona de invernación para S. rufus, ya que en las regiones de reabastecimiento los colibríes permanecen de una a dos semanas Gass 1979;Heinemann 1992). Pero con solo un colibrí que respalde la hipótesis del recambio no se puede establecer el estatus de que El Palmito es un sitio de invernación para S. rufus, por lo que es necesario continuar con esta investigación en los siguientes años. ...
Las comunidades de colibríes han sido estudiadas en relación con sus recursos alimenticios desde hace cinco décadas. Se ha establecido que el principal factor que determina los patrones de abundancia y diversidad de las comunidades de colibríes es la abundancia de las flores que visitan. Así, se ha postulado que la separación ecológica de los nichos puede darse por diversos procesos que pueden ser morfológicos, fisiológicos o incluso conductuales. Otros factores de importancia son las fenologías florales y la migración; sobre todo en regiones altamente estacionales como el Noroeste de México donde un gran número de especies de colibríes son migratorias y existe una gran fluctuación de los recursos florales a lo largo del año. En el presente trabajo de tesis se abordaron cuatro estudios con la comunidad de colibríes en el Noroeste de México y como el uso de los recursos florales influencia su comportamiento, sus patrones migratorios así como la estructura de sus comunidades.
En primer capítulo, determinamos como la conducta y la dominancia influyen en la distribución de los recursos a nivel local. Donde encontramos que el comportamiento agresivo de los colibríes puede estructurar la comunidad y la jerarquía de dominancia está directamente relacionada con el tamaño corporal y no presenta relación con la carga del disco alar o el estatus migratorio. Además, el nivel de dominancia de cada especie está relacionada con la calidad del recurso floral.
En mi segundo capítulo, evaluamos los patrones de fenología migratoria de dos especies de colibríes (Selasphorus rufus y Amazilia beryllina) y si abundancia floral a los patrones estacionales de abundancia de dos especies de colibríes (Selasphorus rufus y Amazilia beryllina). Los resultados muestran que la especie que presenta una ruta migratoria más larga no presenta cambios anuales en su migración (S. rufus), a diferencia de la especie con migración más corta que puede ajustar su migración anual en relación a la cantidad de recursos presentes en cada sitio visitado (A. beryllina). La migración de S. rufus por la región de estudio coincide con la floración de Salvia iodantha. Siendo S. iodantha la principales fuentes de alimento de S. rufus de la región templada del Noroeste de México.
En tercer capítulo, determinamos si existe una preferencia por un tipo de planta en particular utilizando como modelo a dos especies de colibríes de mayor abundancia en la región y de diferente estatus migratorio (S. rufus y A. beryllina). Encontramos que S. rufus se alimento de la especie con la cual coincide su migración en condiciones naturales y en exclusión experimental. A diferencia de A. beryllina, especie que cambio su preferencia en condiciones naturales y al ser ensayada en forma experimental en condiciones de exclusión. Así, la preferencia de un colibrí depende de múltiples factores donde destacan la calidad de los recursos florales, el estatus migratorio así como la jerarquía de dominancia de cada especie de colibrí.
Por último en el cuarto capítulo, se analizaron tres comunidades de colibríes en un gradiente altitudinal y las plantas de las que se alimentan, utilizando la teoría de redes de interacción mutualista. Encontramos que la topología de las redes de interacción cambia en el gradiente altitudinal y que la mayoría de las especies de colibríes las encontramos en dos pisos altitudinales pero desempeñaron papeles diferentes en cada sitio de muestreo. Otro resultado importante fue que las especies núcleo en cada red de interacciones fueron plantas ornitófilas y no ornitófilas. Por último determinamos que la abundancia de colibríes migratorios latitudinales está correlacionada con el número de interacciones así como con los enlaces entre colibríes y plantas.
... Other authors imply that this is part of their definition of territoriality by refering to territories as fixed areas (e.g. Brown and Orians 1970; Gill 1990), by considering the boundaries of the Tenitoriality in Honeyeaters territories (e.g. Hinde 1956; Harris 1970; Wolf 1975 Wolf , 1978 Lyon 1976; Gass et al. 1976; Gass 1979; Carpenter et al. 1983; Tye 1992), or by determining the positions of territories (e.g. Armstrong 1992a). ...
... Several authors have indicated that territorial boundaries were determined by noting consistency of perch occupancy and/or foraging area, and the frequency and location of chases and displays, but did not explain how these factors were used (e.g. Lyon 1976; Gass 1979; Tye 1992). The lack of rigorous definitions of territory boundaries in many studies may reflect the fact that, for at least those species studied, there is a reasonably sharp transition in terms of the behaviour of the territory occupant and any intruders. ...
... The boundaries and size of a bird's territory are often considered important attributes of territorial behaviour (Carpenter and MacMillen 1976a; Wolf 1978; Gass 1979; Pyke 1979; Hixon et al. 1983). Consequently, it is essential that they are carefully defined and accurately measured. ...
We define territorial behaviour as aggressive behaviour that occurs repeatedly in about the same location with associated submissive behaviour on the part of the individuals or groups to which the aggression is directed. Of a worldwide total of about 170 honeyeater species (Meliphagidae), 36 have been described as being territorial and we consider that 28 of these have been shown to satisfy our definition of territoriality. We discuss the consequences of territorial behaviour and the determination of the boundaries and areas of territories. We also review the available information regarding territorial behaviour exhibited by the New Holland honeyeater (Phylidonyris novaehollandiae), the most studied of all honeyeater species. We recommend that future descriptions of territorial behaviour attempt to determine the intensity of the behaviour, sharpness of the territory boundary, degree of exclusive use of the relevant resource, and the extent to which areas separate from the territory are used by the territory owner or owners. For territoriality to become a useful concept for honeyeaters, behaviour that leads to the label of 'territorial' must be fully documented.
... During post-breeding migration, Rufous Hummingbirds use high-elevation alpine meadows, where lateblooming nectar-producing flowers are abundant. 23 Hummingbirds will use a large diversity of flowers including many that are not tubular or red. 24 Hummingbirds can visit four to five thousand flowers a day. ...
... Individuals maximize energy intake and may make daily adjustments to defend territory size. 23 When flower numbers are reduced or destroyed by natural events, such as storms, Rufous Hummingbirds appear to leave the immediate area rather than settle into smaller or lower-quality territories. 50 While it is likely that hummingbirds act as pollinators on the wintering grounds, more research is needed to understand this important ecological role. ...
Revisamos la información científica generada de Selasphorus rufus sobre comportamiento, ecología, necesidades de hábitat y amenazas en todo su rango de distribución geográfico; incluimos aspectos importantes sobre su ciclo de vida y su extraordinaria jornada de este diminuto colibrí. Mencionamos huecos de información que necesitan generase así como las acciones para conservar el colibrí rufo a nivel internacional.
... Social dominance and body size (quantified as length from bill to tail tips from 6 to 22 cm) data were adopted from [56], which defined behavioural dominance as species that have been described in the literature as 'most aggressive' or 'notably aggressive' towards heterospecific hummingbirds in their community or were able to 'monopolize resources'. In a second model we considered four ecological variables related to climate (mean temperature, mean precipitation, temperature predictability, and precipitation predictability [57,58]) by calculating the aggregate mean of each variable across each species' range [55] [61,62], thereby decreasing intersexual competition outside of the breeding season [63]. Although our initial model included monochromic, dichromic and FLP species (with the binary 'no FLP' variable including monochromic and dichromic species), we also ran a model excluding sexually monochromic species for both our analysis of socially relevant traits and ecologically relevant traits (electronic supplementary material, text S7). ...
... Social dominance can directly mediate access to nectar, and differences in rainfall-mediated resource availability can impact intra-and interspecific competition [72], including among seasonal migrants [34,73]. However, since sex separation in migration could also decrease competition [61][62][63], further work is needed to understand how migration might influence competition and ultimately plumage evolution in hummingbirds. Indeed, interspecificand sometimes intersexual-competition is common among hummingbirds [34,[74][75][76], and these socioecological factors may promote the evolution of bright plumage ornamentation as status symbols to mediate such social conflict [65,66]. ...
Differences in the way males and females look or behave are common in animals. However, discrete variation within sexes (sex-limited polymorph-ism) also occurs in several vertebrate and invertebrate lineages. In birds, female-limited polymorphism (FLP) in which some females resemble males in coloration is most prominent in hummingbirds, a group known for its morphological and behavioural sexual dimorphism. Yet, it remains unclear whether this intrasexual colour variation in hummingbirds arises through direct selection on females, or indirectly as a non-adaptive bypro-duct resulting from selection on males. Here, we analysed specimens from more than 300 hummingbird species to determine the extent, evolutionary history and function of FLP. We found that FLP evolved independently in every major clade and occurs in nearly 25% of hummingbird species. Using phylogenetically informed analyses, we rejected non-adaptive hypotheses that FLP is the result of indirect selection or pleiotropy across species. Instead, FLP is associated with ecology, migratory status, and marginally with social dominance, suggesting a socioecological benefit to females. Ultimately, we show that FLP is not only widespread in humming-birds and likely adaptive, but may also be useful for understanding the evolution of female ornamentation in systems under strong sexual selection.
... Numerous studies have documented home range use in fish (Goeden 1978;van Rooij et al. 1996;Shapiro et al. 1994;Zeller 1997a, b;Kramer & Chapman 1999;Bell & Kramer 2000;Eristhee & Oxenford 2001;Bolden 2001;Lembo et al. 2002;Baras et al. 2002). Home range size may be a function of resource distribution (Gill & Wolf 1975;Carpenter & MacMillen 1976Gass et al. 1976;Ewald & Carpenter 1978;Kodric-Brown & Brown 1978;Gass 1979;Frost & Frost 1980;Carpenter 1987;Armstrong 1991;Grant 1997;Maher & Lott 2000), predation risk (Aronson 1951(Aronson , 1971Metzgar 1967;Ambrose 1972;Synder et al. 1976;Clarke et al. 1993), body size and bioenergetic requirements (Harestad & Bunnell 1979, Harvey & Clutton-Brock 1981, Mace et al. 1983, Swihart et al. 1988, Kelt & Van Vuren 1999, review in McLoughlin & Ferguson 2000, intraspecific interactions and territoriality (Burt 1943, Madison 1980, Norman & Jones 1984, Grant et al. 1992, Ribble & Stanley 1998, reproductive dynamics (Hixon 1987, Ostfeld 1990, McCarthy & Lindenmayer 1998, and other factors. Understanding home range size is recognized as a critical question when evaluating the effectiveness of spatial management tools such as marine reserves (Kenchington 1990, Kramer & Chapman 1999, Sale et al. 2005. ...
... Food value theory (Stenger 1958, Wilson 1975 and theoretical and empirical cost-benefit analyses (Brown 1964) have suggested that resource availability plays a major role in determining animal home range overlap (e.g. Gill & Wolf 1975;Carpenter & MacMillen 1976Gass et al. 1976;Ewald & Carpenter 1978;Kodric-Brown & Brown 1978;Gass 1979;Frost & Frost 1980;Carpenter 1987;Armstrong 1991;Maher & Lott 2000). A model of brown bear (Ursus arctos) home range use by predicts that in areas of high habitat quality, populations will be characterized by small home ranges and high percentages of home range overlap, and in areas of moderate habitat quality, home ranges will be larger with decreased overlap. ...
Movement patterns and space use by mature fishes are critical in determining the effectiveness of marine reserves in conserving spawning stock biomass and/or providing biomass to adjacent fisheries through 'spillover'. Home range sizes, activity patterns, site fidelity and habitat preferences were determined for acoustically-tagged snappers and groupers using a rigorously-calibrated array of omnidirectional hydroacoustic receivers deployed in the diverse coral reef environments of a no-take marine reserve (NTMR) network in the Dry Tortugas, Florida. An individual-based localizing tendency model of reef fish movement was parameterized from fine-scale acoustic telemetry data and integrated into a Spatial Management Performance Assessment (SMPA) simulation model for reef fish populations developed to quantitatively evaluate performance of no-take marine reserves in the Dry Tortugas, Florida. Spatially-explicit SMPA models were parameterized for three overfished stocks in the lucrative snapper-grouper fishery: red grouper (Epinephelus morio), black grouper (Mycteroperca bonaci), and mutton snapper (Lutjanus analis). SMPA models were used to evaluate the impacts of a variety of life histories, movement strategies and speeds, and management regulations upon long-term stock sustainability, as measured by annual changes in spawning potential ratio (SPR), and long-term stock productivity, as measured by annual changes in fisheries yield-in-weight per recruit (Yw/R). Under assumptions of constant regional fishing pressure, constant recruitment, and 'realistic' fish movement, SMPA simulation runs from initial conditions in 2000 suggested that by 2014, the Tortugas NTMR network should function to restore red grouper populations to 30% SPR, a Federal management benchmark for sustainability. Mutton snapper were the most mobile of the species investigated; if mutton snapper movements are ignored, their population is predicted to attain 30% SPR by 2014, but given 'realistic' mobility, they may not attain this target by 2021 without additional protections. Black grouper are currently fished at over 9 times sustainable levels. SMPA simulations suggest coupling an increase in minimum size at capture of 20 - 25 cm with NTMR implementation would result in substantial short term losses in yield, but would restore both black grouper and mutton snapper populations to 30% SPR by 2021 and lead to increased long-term yields. Although marine reserve sites are often chosen opportunistically, these findings strongly suggest that reserve designs (e.g. proper sizes and configurations) must take into account the scales and patterns of movement exhibited by the exploited stocks they are intended to protect. These modeling efforts also suggested reserves are not a panacea; in order to promote sustainability for severely depleted stocks, they must be accompanied by an overall reduction in fishing capacity. Although important questions remain concerning the movements of reef fish in response to habitat and density dependent processes, our analyses of realistic reef fish behaviors suggest that the NTMRs of the Dry Tortugas promote substantial gains in SPR, promoting long-term stock sustainability and enhanced egg production. Increased rates of movement diminish these benefits, but may also mitigate short-term losses in yield associated with NTMR establishment.
... The size and location of home ranges, therefore, are temporally and spatially dynamic, given the nutritional requirements and life-history stage of an animal (Zurell et al., 2018), and the distribution and abundance of food (Gautestad & Mysterud, 2005;Takasaki, 1981;Wang & Grimm, 2007). Habitat quality has perhaps the strongest influence on the spatial structure of a home range (Gass, 1979;Powell et al., 1997). Changes in habitat quality can have varying influences on home ranges from prompting seasonal shifts of home ranges (e.g., migration; Taylor & Norris, 2007) to smaller scale changes in the size and location of home ranges (van Beest et al., 2011;Wolff, 1984). ...
The spatial distribution of animals has consequences for nutrition, predator–prey dynamics, spread of diseases, and population dynamics in general. Animals must establish a home range to secure adequate resources to fuel their energy needs. Home ranges, therefore, are temporally and spatially dynamic, given the changing requirements of an animal and the availability of resources on the landscape. We used data from two populations of bighorn sheep with contrasting population dynamics following pneumonia epizootics and different habitat quality on their summer range to test the hypothesis that the distribution and size of home ranges are influenced by environmental conditions and reproductive status. We used a combination of data from 768 vegetation transects and remotely sensed metrics to index forage quality of consecutive biweekly home ranges for 27 bighorn sheep, June–August 2019–2021. There were population differences in home range dynamics that were consistent with resource limitations in the population declining in abundance. Animals in both populations increased the size of their home range through the summer in association with declining forage quality indexed by plant phenology. Furthermore, animals in the Whiskey Mountain population without offspring had home ranges more than twice the size of animals with offspring, whereas there were no differences in the home range size between animals with and without offspring in Jackson. We demonstrated that limitations young offspring impose on space use of a mother may have consequences for animals living where larger home ranges are needed to secure adequate resources—sheep on Whiskey Mountain had to travel 1000 m from escape terrain to access the same amount of biomass that the Jackson sheep could access directly adjacent to escape terrain. Forage quality and availability influence movement and space use. In the presence of disease, movement and space use may influence pathogen transmission and persistence. Thus, forage availability may play an indirect role in population dynamics in the presence of disease, which is another line of evidence for how environmental and nutritional conditions may influence population dynamics when coping with disease.
... In addition, the ruby-throated hummingbird (Archilochus colubris) engages in an annual migratory journey from breeding grounds throughout Eastern North America to wintering grounds as far south as Central America. If measured in terms of body lengths traveled, small North American hummingbirds engage in some of the longest distance aerial migrations of any species (Gass 1979). In doing so, they demonstrate a remarkable ability to sustain high rates of metabolism using endogenous lipids, an ability not shared by mice, rats, or humans (McCue and Pollock 2013). ...
Hummingbirds are very well adapted to sustain efficient and rapid metabolic shifts. They oxidize ingested nectar to directly fuel flight when foraging but have to switch to oxidizing stored lipids derived from ingested sugars during the night or long-distance migratory flights. Understanding how this organism moderates energy turnover is hampered by a lack of information regarding how relevant enzymes differ in sequence, expression, and regulation. To explore these questions, we generated a chromosome scale genome assembly of the ruby-throated hummingbird ( A. colubris ) using a combination of long- and short-read sequencing, scaffolding it using existing assemblies. We then used hybrid long- and short-read RNA sequencing of liver and muscle tissue in fasted and fed metabolic states for a comprehensive transcriptome assembly and annotation. Our genomic and transcriptomic data found positive selection of key metabolic genes in nectivorous avian species and deletion of critical genes ( SLC2A4 , GCK ) involved in glucostasis in other vertebrates. We found expression of a fructose-specific version of SLC2A5 putatively in place of insulin-sensitive SLC2A5 , with predicted protein models suggesting affinity for both fructose and glucose. Alternative isoforms may even act to sequester fructose to preclude limitations from transport in metabolism. Finally, we identified differentially expressed genes from fasted and fed hummingbirds suggesting key pathways for the rapid metabolic switch hummingbirds undergo.
... FURTHER READING Calder and Jones, 1989, Car¬ penter and Hixon, 1988,Gass, 1979,Hiebert, 1991Johnsgard, 1983, Paton and Carpenter, 1984,Tyrell and Tvrell, 1984 HABITAT REQUIREMENTS: From lowlands to mon¬ tane parks, always associated closely with water, especially wooded streams and rivers, but also lakes, ponds, and any other permanent body of water providing fish. Nests in horizontal burrow exca¬ vated in vertical bank along streams and rivers. ...
... During the boreal summer, male rufous hummingbirds (Selasphorus rufus) hold territories containing hundreds to thousands of flowers. These birds will adjust the size of the territory they defend in relation to both the density of flowers [15,16] and the flower species within the territory [17]. When discriminating between patches of flowers, these birds appear to also be able to use an approximate number system [18] and can reliably discriminate between the quality of a flower's reward both in nectar concentration and volume [19]. ...
Rufous hummingbirds (Selasphorus rufus) will readily learn the location and the colour of rewarded flowers within their territory. But if these birds could apply a relational concept such as 'the larger flowers have more nectar', they could forego learning the locations of hundreds of individual flowers. Here, we investigated whether wild male territorial rufous hummingbirds might use 'larger than' and 'smaller than' relational rules and apply them to flowers of different sizes. Subjects were trained to feed consistently from one of two flowers. Although the flowers differed only in size, the reward was always contained in the same-size flower. The birds were then tested on a choice of two empty flowers: one of the familiar size and the other a novel size. Hummingbirds applied relational rules by choosing the flower that was of the correct relational size rather than visiting the flower of the size rewarded during training. The choices made by the hummingbirds were not consistent with alternative mechanisms such as peak shift or associative learning. We suggest that while hummingbirds are very good at remembering the spatial locations of rewarding flowers, they would be able to use relative rules when foraging in new and changing environments.
... In addition, ruby-throated hummingbirds engage in an annual migratory journey from breeding grounds throughout Eastern North America to wintering grounds as far south as Central America. If measured in terms of body lengths traveled, small North American hummingbirds engage in some of the longest distance aerial migrations of any species (Gass 1979). In doing so, they demonstrate a remarkable ability to sustain high rates of metabolism using endogenous lipids, an ability not shared by mice, rats, or humans (Marshall D. McCue and Pollock 2013). ...
Hummingbirds are very well adapted to sustain efficient and rapid metabolic shifts. They oxidize ingested nectar to directly fuel flight when foraging but have to switch to oxidizing stored lipids derived from ingested sugars during the night or long-distance migratory flights. Understanding how this organism moderates energy turnover is hampered by a lack of information regarding how relevant enzymes differ in sequence, expression, and regulation. To explore these questions, we generated a chromosome level de novo genome assembly of the ruby-throated hummingbird (A. colubris) using a combination of long and short read sequencing and scaffolding using other existing assemblies. We then used hybrid long and short-read RNA-sequencing for a comprehensive transcriptome assembly and annotation. Our genomic and transcriptomic data found positive selection of key metabolic genes in nectivorous avian species and a deletion of critical genes (GLUT4, GCK) involved in glucostasis in other vertebrates. We found expression of fructose-specific GLUT5 putatively in place of insulin-sensitive GLUT4, with predicted protein models suggesting affinity for both fructose and glucose. Alternative isoforms may even act to sequester fructose to preclude limitations from transport in metabolism. Finally, we identified differentially expressed genes from fasted and fed hummingbirds suggesting key pathways for the rapid metabolic switch hummingbirds undergo.
... This allows adult males to start fall migration earlier than adult females and young. This adaptation in migration timing likely decreases competition for quality food resources during migration (Gass 1979, Newton 2006. The agespecific pattern of young birds beginning their fall migration later, and having a more westerly route, raises several questions. ...
The effective conservation of birds requires knowledge of species-specific population dynamics. Yet these dynamics during migration and across age and sex categories are poorly understood for small birds. The goal of this study was to assess large-scale fall migration patterns of Rufous Hummingbirds (Selasphorus rufus). Because the age and sex categories of this species depart from the breeding grounds and arrive from migration on different weeks, we predicted that each might use different migration routes, differ in migration speeds, and vary in their weekly distributions. Rufous Hummingbirds are among a few declining species for which a large amount of banding data is available during migration and across the migration corridor. We assembled a large hummingbird capture dataset (28,948 captures; 459 unique locations; fall migrations from 1998 to 2013) and used the centroid location of each age-sex-year-week group to calculate migration routes, timing, and speed. We used a utilization distribution kernel to measure distributions during migration. Adult females tended to have a southbound migration route parallel and between those of young and adult males. Moreover, a greater number of young birds migrated south through California in comparison to adult females and adult males. Our results suggest that the migration of each age-sex category is separated by approximately two weeks with adult males migrating first, followed by adult females, and then the young of both sexes; yet migration speed was not statistically different among categories. Last, adult males were captured within a smaller geographic distribution, i.e., the area during any given week of migration, compared with adult females and young. We conclude that different age-sex categories of Rufous Hummingbirds use alternative routes and differ in migration phenology and distributions. Our results suggest that the age-sex categories could be affected differentially by habitat loss, phenological changes, and climates during migration. Considering such demographic migratory dynamics could improve conservation outcomes.
... Many studies have shown that for a particular species territory size is inversely related to food abundance (e.g. Gass 1979, Hixon et al. 1983, Davies & Lundberg 1985, Smith & Shugart 1987. ...
Habitat requirements of the White-browed Babbler in box-ironbark forest focussing on the trade-off between foraging and predation
... Later-migrating juveniles might migrate through middle elevations in southeastern Arizona because the region provides more food resources than the Rocky Mountains at this time of year. Alternatively, juveniles may be forced to use suboptimal habitats because they are less successful at competing with adults for territories along their migration routes (Gass 1978). Because juveniles migrate later than adults, this alternative is unlikely. ...
We examined the distribution and abundance of hummingbirds at two study sites in southeastern Arizona, where we banded over 8000 individuals and 11 species in a 6-year period. We trapped approximately once a week from April to October at each site, from 1988–1992 at Sonoita, in oak woodlands, and 1991–1993 at Harshaw Creek, in a riparian area. Anna's (Calypte anna), Black-chinned (Archilochus alexandri), and Rufous (Selasphorus rufus) Hummingbirds were the most abundant species. At Harshaw Creek, Broad-billed (Cynanthus latirostris) and Costa's (Calypte costae) Hummingbirds occurred in significant numbers. A massive fall migration occurred at both sites, but few hummingbirds moved northward in spring. The large numbers of migrants were spaced over time within seasons, and the timing of peak migration for a species varied among years. Fall-migrant Black-chinned Hummingbirds peaked earliest with adult males preceding adult females and juveniles, followed by Rufous Hummingbirds (predominantly juveniles), then Anna's Hummingbirds. Of the most abundant species, Rufous Hummingbirds used the sites only during their migration, and the other four species bred at one or both sites. During the first three years of feeder use at Harshaw Creek, Anna's Hummingbirds significantly increased in numbers but other species did not. We also report how the age and sex classes for the common species varied in abundance between sites and among years.
Distribución y Abundancia Estacional de Colibríes en Encinales y Comunidades Riparias en el Sureste de Arizona
Resumen. Analizamos la distribución y abundancia de colibríes en dos sitios en el sureste de Arizona, donde se anillaron más de 8000 individuos de 11 especies durante un período de seis años. Durante los meses de abril a octubre entre 1988 y 1993, se capturaron colibríes una vez por semana, en un área de encinal abierto en Sonoita y por tres años en un área riparia en Harshaw Creek. Las especies más abundantes fueron: Calypte anna, Archilochus alexandri y Selasphorus rufus; en Harshaw Creek, Cynanthus latirostris y Calypte costae ocurrieron en cantidades significativas. En los dos sitios ocurrió una migración hacia el sur en forma masiva durante el otoño, pero muy pocos colibríes migraron hacia el norte durante la primavera. Los grandes números de migrantes estuvieron espaciados en el tiempo dentro de cada estación, y la fecha pico de migración para cada especie varió año a año. Durante la migración de otoño, el pico de migración más temprano fue el de A. alexandri, cuyos machos adultos migraron antes que las hembras adultas y los juveniles, seguido por el pico migratorio de S. rufus (dominado por juveniles) y después por el de C. anna. Una de las especies más abundantes (S. rufus) usa los sitios solamente durante su migración, mientras que las otras cuatro especies se reproducen en uno o ambos sitios. Durante los tres primeros años en que los colibríes utilizaron bebederos en Harshaw Creek, C. anna aumentó en forma significativa, pero las otras especies no. También reportamos cómo variaron las abundancias de las distintas clases de edad y sexo de un sitio a otro y entre los diferentes años para las especies más comunes.
... Dominance (both intra and interspecific interactions) in hummingbirds has been found to be associated with the individual physical state, sexual dimorphism, body size, wing disc chord loading, species identity (e.g., some species dominate others at floral patches or feeders) and territorial quality (Kodric-Brown and Brown 1978;Carpenter et al. 1993;Ornelas et al. 2002;Stiles et al. 2005;Németh and Moore 2012). These characteristics have been postulated and tested in hummingbird species at particular moments of their biological cycles such as migration and reproduction (i.e., Gass 1979;Ewald 1985). It has also been suggested that variation in behavioral profile or Bpersonalities^may affect the establishment of dominance relationships and risk sensitivity, where previous research has found hummingbirds to show a steroid-correlated boldness scale (Goloff and Burch 2012;Chávez-Zichinelli et al. 2014). ...
The role of badges as indicators of contest ability has been previously described. In hummingbirds, the exhibition of a badge is expected to save energy expenditure in agonistic interactions and to favor energy intake. Here, we investigate whether variable supercilium size in the white-eared hummingbird has a role in dominance status signaling. Firstly, 45 hummingbird males were captured and their superciliums were photographed to investigate variation in size and any possible allometric relationships. Secondly, 42 male birds were used to analyze whether the supercilium has a role in dominance status signaling in a dyadic contest. We found that supercilium size varied continuously but that despite variability between individuals, there was no relationship between supercilium size and body size. However, our dyad experiment indicated that birds with larger badges were able to make more visits to the feeders than individuals with smaller badges. We suggest a status signaling function of the supercilium.
... While we cannot know for sure why activity budgets did not change in our study while territory area and diet did, it may in part have been because there was simply less food available, even when territory expansion was incorporated, and hence no increase in foraging time. In studies in which activity budgets did shift towards more foraging, the resources acquired by territory expansion led to no overall change in the total quantity of resources within the territory, though they were more dispersed (Gass, 1979;Gill and Wolf, 1975). Other factors apart from resources, especially population density, can impact territory size (Schoepf et al., 2015) and may have limited how much territory expansion was possible in our system, leaving birds with fewer resources within their territory than before robbing treatments, and making an increase in foraging time ineffective due to a decrease in available food. ...
While the effects of nectar robbing on plants are relatively well-studied, its impacts from the perspective of the pollinators of robbed plants is not. Numerous studies do consider the impacts of robbing on pollinator visitation to robbed plants, but rarely do they focus on its scaled-up impacts on individual pollinator behavior. We used radio telemetry to track the spatial and behavioral responses of the territorial hummingbird Aglaeactis cupripennis to experimental nectar-robbing over a period of several days. Simulated nectar robbing impacted foraging behavior by increasing territory area, distance flown, and reliance on novel food resources, especially small-bodied flying insects. We did not observe any impact on the amount of time individuals spent foraging, nor did we observe territory abandonment. These findings indicate that nectar robbing may impose a significant energetic cost on pollinators via increased flight distances and shifts towards potentially less profitable food resources, and demonstrate the importance of quantifying the indirect effects of nectar robbing on pollinators in addition to plants.
... In our case patches with flowers of A. inaequidens provided a large amount of calories per flower and generally a reduced number of flowers than the patches with flowers of S. iodantha and C. thyrsoideum. Even a patch with few flowers, by providing more calories per flower, is more profitable to defend for a hummingbird (Kodric-Brown & Brown 1978, Gass 1979, Montgomerie et al. 1984, Carpenter 1987. ...
... Individuals may adjust territory size to ensure the resources necessary for survival and breeding (Dunk & Cooper, 1994;Gass, 1979). Two conflict patterns were detected among different studies. ...
Both mean group size (MGS) and mean group density (MGD) are critical indices to characterize a population of cooperatively breeding birds. When a population reaches its carrying capacity, both long-term MGS and long-term MGD will remain relatively stable. However, there has been little study of how these two variables relate. The Masked laughingthrush Garrulax perspicillatus is a cooperatively breeding bird living in fragmented habitats. During 2010 and 2012-2016, we used song playback to observe and confirm the group sizes and territory ranges of the birds and the data of bird presence to determine habitat suitability. By grouping the nearest territories according to their geographical coordinates, we divided the whole study area into 12 subareas and the whole population into 12 subpopulations. Then, we calculated both MGS and MGD for different time durations for each subpopulation. Finally, using MGD as independent variable and MGS as the dependent variable, we explored the correlations between MGS and MGD by fitting quadratic functions and modeling quadratic regression. Both MGS and MGD were averaged for different time durations and were cross-related. Our results show that the MGS for more than 2 years significantly correlated with MGD for more than 3 years in a reverse parabolic shape, differing from that of short-term effects. Our findings suggest that long-term MGD is a better predictor of long-term habitat quality and that long-term MGS is determined by long-term habitat quality in Masked Laughingthrushes. Based on above findings, we can infer that: (1) Long-term habitat quality determines the long-term MGS, but it sets no prerequisite for the status and source of group members; (2) Long-term MGS in certain populations is adapted to the corresponding level of long-term habitat quality, it facilitates us to predict the helper effects on current or future survival or reproduction in different situations. These findings and inferences are both helpful for us to understand the evolution of cooperative breeding.
... Our study fills a huge gap in the natural history of Rubythroated Hummingbird migration by providing some of the first information on the temporal pattern of arrival, arrival condition, stopover biology (FDR and stopover duration), and departure (flight range), as well as reporting on age-and sex-dependent effects. Much of the information available on hummingbird migration has depended on work with Rufous Hummingbirds in western North America (e.g., Gass et al. 1976, Kodric-Brown and Brown 1978, Gass 1979, Carpenter et al. 1991, 1993a, 1993b, 1993c. Rufous Hummingbirds exhibit age-and sexdependent migration as well as social dominance during stopover (Carpenter 1993b, and references therein). ...
Surprisingly little is known about the migration and stopover biology of Ruby-throated Hummingbirds (Archilochus colubris), and even less is known about their sex- or age-dependent migration. First, we provide basic information on the migration and stopover biology of this species along the northern coast of the Gulf of Mexico during autumn, including phenology, stopover duration, fuel deposition rate (FDR), arrival mass, and estimated flight ranges. Second, we investigate whether these stopover variables are influenced by age or sex. Age-dependent migration is expected because young, hatch-year birds on their first migration lack the experience of older individuals. Sex-dependent migration is expected because of sexually dimorphic characteristics in wing morphology and body size. We obtained information on arrival mass, phenology, FDR, stopover duration, and estimated flight ranges through banding data, passive integrated transponder tags, radio telemetry, and color marking at a long-term migration station along the northern coast of the Gulf of Mexico. Our data provide strong evidence for age-dependent migration and only weak evidence for sex-dependent migration. Older birds arrived earlier, had larger fuel loads, and had shorter stopover durations than younger birds. In younger birds, we found no effect of sex on FDR, arrival mass, stopover duration, or phenology. Older males arrived with larger fuel loads than females. Finally, we used flight simulation software and our data to estimate that males and older birds were capable of longer potential flight ranges than either females or younger birds.
... These results suggest that Red-eyed Vireos can secure nestling stage food resources at the time of territory selection, using canopy foliage density as a cue. It was surprising that territory size was not inversely correlated with competitor density, given the number of previous studies that have found this negative correlation (e.g., Morse 1976, Gass 1979, Myers et al. 1979, Dunk and Cooper 1994). It is possible that the two ways in which we quantified competitor density did not necessarily reflect the frequency of intrusions or territorial boundary conflicts that would incur a direct cost to maintaining a territory of a given size. ...
The food value theory of territoriality predicts an inverse relationship between territory size and food density. However, several non-mutually exclusive hypotheses can explain this relationship. We studied the relationship between foliage density, food density, competitor density, and territory size of the Red-eyed Vireo (Vireo olivaceus), a canopy-dwelling, insectivorous songbird, in the Monongahela National Forest, West Virginia, USA, 1995-1998. First, we established the relationship between territory size and the canopy-tree foliage density. We then utilized the relationship between foliage density and foliage arthropod density (in particular, Lepidoptera larvae) to evaluate whether an inverse correlation between food density and territory size existed and to examine the proximate cues that Red-eyed Vireos used to adjust territory size. Foliage density in a habitat patch was used by Red-eyed Vireos as a proximate cue to set the size of a three-dimensional territory volume that ultimately corresponded to the "average" caterpillar density on those trees during the nestling stage. Territory volumes were smaller where foliage density was greater. Two measures of competitor density were not inversely correlated with territory size. These results support the structural-cues hypothesis for a species that forages in the structurally complex foliage of deciduous forests, and they are consistent with the food-value theory of territoriality. Caterpillar density varied widely over the course of the breeding season, among locations and among tree species, reaching a low during the nestling stage of the breeding cycle. Yet, the total territory volume utilized by Red-eyed Vireos was inversely related to the density of caterpillars during this stage (i.e., when they would be needed as a food source to provision young), consistent with the food-value theory. Food availability at the time of territory selection was not a reliable cue for future food resources because of spatial and temporal variability in caterpillar density. Instead, a stable structural cue, foliage density, was highly predictive of caterpillar density during the nestling stage of an average, or typical, year. This study suggests that Red-eyed Vireos can reliably secure food resources for nestlings at the time of territory establishment, using foliage density as a cue.
... If adult Rufous migrate through Arizona at higher elevations, our study would miss this migration. Alternatively, juveniles may be forced to use suboptimal habitats because they are less successful at maintaining territories along their migration routes than adults (Gass 1978). Whether our study sites represent sub-optimal habitats for migrating Rufous or a better food source at the later migration time of juveniles is unknown. ...
We examined the distribution and abundance of hum- mingbirds at three study sites in southeastern Arizona, where over 8,000 individuals of twelve species were banded. Banding occurred at two sites in the early 1990s and is currently active at the third. Anna's (Calype anna), Black-chinned (Archilochus alexandri), and Rufous (Selasphorus rufus) Hummingbirds were the most abundant species. A massive southbound fall migration occurred at the study sites with fewer hum- mingbirds moving northward in spring. The large num- bers of migrants were spaced over time within seasons, and the timing of peak migration for a species varied among years. Fall-migrant Black-chinned peaked earli- est, followed by Rufous (predominantly juveniles), then Anna's. Of these species, Rufous used the sites during migration only while the other species bred at one or more sites. Because the timing of migration differed among species, the resources critical for mi- gration of each species likely differed as well. The implications for hummingbird conservation are discussed.
... Most tropical hummingbirds overlap extensively in the flowers they exploit and compete aggressively for the available resources (Feinsinger 1978, Gass 1978, 1979; others, such as the hermits, have elongated bills which allow them more or less exclusive access to nectar in long-tubed flowers, which less specialized hummingbirds cannot reach (Snow & Snow 1972, 1980, Stiles 1975. ...
Between October 1987 and September 1989, the British Ornithologists' Union Colombia Expedition recorded 16 species of hummingbird at Matamatá in the Amacayacu National Park, Amazonas, Colombia. Most of these species were resident breeders at the study site although two appeared to be local migrants. Six species of hermit hummingbirds (subfamily Phaethornithinae) occurred at Matamatá; although very similar in general morphology and behaviour, they showed different preferences for habitat, food plants and foraging technique. Hermits were predominant in the forest, but in areas of secondary vegetation and along riverine borders, “typical” hummingbirds (subfamily Trochilinae) were more common. The study site consisted of terra firme and várzea forest and an area of riverine secondary vegetation and contained around 60 species of flowering plants visited by hummingbirds. In contrast with most groups of organisms, hummingbirds and hummingbird-pollinated plants had similar species diversity in primary forest and secondary habitats. The overall abundance of hummingbirds and flowers was significantly higher in areas of riverine secondary growth. The hummingbird community at Matamatá is remarkably species rich when compared with study sites elsewhere in North and South America. However, random null model comparisons among Amazonian hummingbird communities reveal that they share many characteristics in their structure and show a high degree of species overlap.
... Many avian studies have shown that territory owners vary their territory size in relation to resource abundance . For example, nectar-feeding birds show daily changes in territory size depending on natural variation in their food supply (Gill and Wolf 1975, Gass 1979) or experimental manipulations (Eberhard and Ewald 1994). However, other species maintain a fixed territory size despite fluctuations in food supply. ...
Cooperatively breeding groups may be constrained in size by the territory available to them, or territories may be expanded to accommodate extra group members. Here, we show that there was no relationship between the number of adult green woodhoopoes Phoeniculus purpureus in a group and the size of its territory. Furthermore, territories were remarkably stable between seasons, with no significant changes in area, despite fluctuating group sizes. These results suggest that food was not limiting at the group sizes found in this study: sufficient resources were available within existing territories for groups that were expanding in size. Following an increase in group membership, a larger proportion of the available area was utilised. Groups also used a larger area in the non-breeding season compared to when breeding: in the latter instance, foraging was concentrated in the vicinity of the nest.
Many fire‐prone forests are experiencing wildfires that burn outside the historical range of variation in extent and severity. These fires impact pollinators and the ecosystem services they provide, but how the effects of fire are mediated by burn severity in different habitats is not well understood. We used generalized linear mixed models in a Bayesian framework to model the abundance of pollinators as a function of burn severity, habitat, and floral resources in post‐fire, mid‐elevation, conifer forest, and meadow in the Sierra Nevada, California. Although most species‐level effects were not significant, we found highly consistent negative impacts of burn severity in meadows where pollinators were most abundant, with only hummingbirds and some butterfly families responding positively to burn severity in meadows. Moderate‐severity fire tended to increase the abundance of most pollinator taxa in upland forest habitat, indicating that even in large fires that burn primarily at high‐ and moderate‐severity patches may be associated with improved habitat conditions for pollinator species in upland forest. Nearly all pollinator taxa responded positively to floral richness but not necessarily to floral abundance. Given that much of the Sierra Nevada is predicted to burn at high severity, limiting high‐severity effects in meadow and upland habitats may help conserve pollinator communities whereas low‐ to moderate‐severity fire may be needed in both systems.
Hummingbirds of the species Selasphorous platycercus and Selasphorous rufus were studied in Colorado, where they displayed territorial behaviour at feeders containing 10%, 20%, and 30% sucrose solutions. At each of the three energy availability levels, the number of invaders, the number of territory owners, and the level of Defence were recorded. After being forced out of their breeding area by Rufous Hummingbirds, Broad-tailed Hummingbirds only bother to defend locations of inferior quality. Both Wide-tailed and Rufous hummingbirds, while keeping tabs on important locations, resort to more flamboyant modes of behaviour, such as extended pursuits augmented with chip cries and aimless wing flapping. According to certain probes, a chase is ready to start if chip calls and hovering are any indication. However, I learned that when an intruder was present, it was only natural to want to get rid of them. Hovering and chip calls were utilised to increase the intensity of the chase. Broad-tailed Hummingbirds were less likely than Rufous Hummingbirds to make chip sounds or hover without giving pursuit.
Background
Many species of birds are morphologically and physiologically adapted for migration. Migratory movements of birds can range from thousands of kilometers, such as when birds migrate from wintering to breeding sites in summer, to several kilometers, such as when birds migrate among habitats in a single mountain system. The main factor that influences bird migration is the seasonal fluctuation of food resources; climate, predation, competition for resources and endogenous programming are also important factors. Hummingbirds are highly dependent on nectar, so their migration is likely correlated with the blooming of plant species. The ecological implications of altitudinal migration in the mountains of North America as well as the latitudinal migration of Selasphorus rufus through Mexico are still poorly understood. To explore these issues, over three non-consecutive years, we evaluated interannual variation in the phenologies of a latitudinal migrant ( S. rufus ) and an altitudinal migrant ( Amazilia beryllina ) and their visited plants.
Methods
We assessed the relationship between two migratory hummingbirds and flower abundance in 20 fixed-radius plots (25 m radius). All available flowers were counted along transects (40 × 5 m) inside each fixed-radius plot. Sampling was performed every 10 days from November 12 through February 20 of 2010–2011, 2013–2014 and 2015–2016, resulting in a total of 11 samples of each plot per period. Phenological variation and the relationships among hummingbird abundance, flower abundance and vegetation type were evaluated using a generalized additive mixed model.
Results
S. rufus abundance was related to sampling time in the first and third periods; this relationship was not significant in the second period. A. beryllina abundance was related with the sampling time over all three periods. The abundance of S. rufus hummingbirds was significantly related to the number of Salvia iodantha flowers. The abundance of A. beryllina hummingbirds was related to the number of S. iodantha and Cestrum thyrsoideum flowers and the total number of flowers. We found a non-significant correlation between S. rufus and A. beryllina abundance and vegetation types.
Conclusion
Contrary to expectations, the long-distance migration of S. rufus was not consistent over the sampling periods. The migration of S. rufus through the study region may be altered by changes in climate, as has occurred with other species of migratory birds. In the present study, the migration of S. rufus was correlated with the blooming of S. iodantha . In comparison, the altitudinal migrant A. beryllina responded to the availability of floral resources but was not associated with a particular plant. The migration of this latter species in the area probably depends on multiple factors, including climatic and demographic factors, but is particularly dependent on the supply of floral resources and competition for these resources.
Este trabalho teve por objetivo acompanhar e analisar as interações inter e intra-específicas de beija-flores e como estas interações mudaram ao longo do ano. O estudo foi realizado em um remanescente de floresta no município de Piraquara, Paraná. Beija-flores foram filmados mensalmente entre março de 2008 e abril de 2009. Foi possível identificar indivíduos focais, medir intervalos de tempo durante o qual o indivíduo focal ficou no bebedouro e anotar o momento e a espécie envolvida em uma interação. A espécie mais comum foi Leucochloris albicollis que foi observado em 2.300 visitas, seguido por Colibri serrirostris, Amazilia versicolor, Florisuga fusca e Thalurania glaucopis. Há variações entre as espécies no tempo de exploração do recurso: L. albicollis tende a ficar 21s em cada visita, em contraste com F. fusca que tende a ficar somente 7s. As conseqüências destas interações complexas podem estruturar a comunidade com uma hierarquia flutuante, que varia ao longo do ano.
How the local density of territorial animals responds to changes in food abundance will depend on the flexibility of territory size. Quantitative estimates of territory size over a broad range of food abundance are relatively rare because of the difficulty of measuring food abundance in the wild.
Stream salmonids are an ideal model system for investigating flexibility in territory size, because food abundance can be quantified in the field and manipulated in the laboratory. We conducted a meta‐analysis to test whether territory size decreases with increasing food abundance, and a mixed model analysis to test among three competing predictions: with increasing food abundance, territory size will be (1) fixed—the slope of a regression of log territory size vs. log food abundance = 0; (2) flexible and decreasing, as if individuals are defending a fixed amount of food—a slope = −1; and (3) initially compressible, but with an asymptotic minimum size—a slope between 0 and −1.
We collected data from 16 studies that manipulated or measured food abundance while monitoring changes in territory size of young‐of‐the‐year salmonids; 10 were experimental laboratory studies, whereas six were observational field studies.
Overall, territory size decreased significantly with increasing food abundance; the weighted average correlation coefficient was −0.31. However, the estimated slope of the relationship between log territory size and log food abundance was only −0.23, significantly different from 0, and also significantly shallower than −1.
Our estimated slope suggests that attempts to increase the density of territorial salmonids by increasing food abundance and reducing territory size will be inefficient; a 20‐fold increase in food abundance would be required to double population density. Our analysis may also have implications for other species with a territorial mosaic social system—i.e. contiguous territories. In these social systems, social inertia will dampen any effects of changes in food abundance on the local density of settlers, compared to non‐territorial species or those with non‐contiguous territories.
Over the past 100 years, much has been learnt about what limits the numbers of birds, and many field experiments have been conducted to check ideas. Such understanding is essential for the effective conservation or other management of bird populations. All the main factors likely to affect bird numbers, whether food or nest-sites, predators, pathogens or competitors, have been found to limit the numbers of one species or another. The same species may be limited by different factors in different areas or in different years. Some species may be limited by a combination of factors, which interact in their effects on population levels. Long-term trends and/or year-to-year fluctuations suggest that some migratory bird populations are limited primarily in their breeding areas, and others primarily in their wintering areas. Other aspects of population regulation are also discussed, including demographic factors (births, deaths and movements), and the role of territorial and other aggressive behaviour in the limiting process.
(1) We have previously shown how pied wagtails defend winter feeding territories along a river. Owners walk a regular circuit round their territories, exploiting a renewing food supply (insects washed onto the river banks). (2) We use a simulation model to investigate the effect of territory size on the owner's feeding rate. Larger territories can yield more food because the longer the foraging circuit the greater the time for resource renewal between successive visits to the same stretch. But larger territories cost more to defend. (3) Simulation shows that the territory size that maximizes feeding rate or energetic gain varies with the rate of food renewal, smaller territories being better when renewal is fast and larger ones when it is slow. (4) Real wagtails did not track these short-term optima by changing territory size, but maintained a territory size of about 600 m throughout the winter. (5) We show that this territory size may promote an owner's long-term chances of over-winter survival. If territory size is less than 600 m, then many days would yield a feeding rate inadequate for survival, while defending a territory larger than 600 m would not increase the number of profitable feeding days. (6) We use simulation to explore how changes in intruder pressure, walking speed and ability to detect intruders affect feeding rate; owners would achieve only a slight gain in feeding rate by improving their detection ability beyond the observed values.
Latitudinal differences in territorial behavior are considered to have great influence on differences in life-history strategies of Nearctic and Neotropical birds. Most territorial behavior of tropical birds has particularities that cannot be explained only by theories from studies of birds in temperate regions. We evaluated the territorial system of the cooperative-breeding White-banded Tanager (Neothraupis fasciata) in central Brazil’s savanna and present results on stability of territory site occupation, relationship between territory size and group size, and dispersal patterns. Territories (n ¼ 27, mean per season) were monitored for 3 yr in a protected area in the cerrado of central Brazil and were defined by the minimum convex polygon method. Territory size averaged 3.7 6 0.6 ha, and was defended by all individuals of groups of 2–8 individuals (mean ¼ 3.4 6 1.2). We recorded 44 dispersal events between territories, and most individuals dispersed distances equal to one territory in length. Males tended to stay in the same territory, whereas females dispersed. Our results support hypotheses that predict year-long territory defense for tropical birds. Territory size reflected group size, corroborating the hypothesis that individuals adjust the territory size to ensure the amount of resources for survival.
Their territory holding, coupled with a number of other important features of the rufous hummingbird, has allowed us to investigate the cognitive abilities of these animals in the field. These birds can remember, so as to subsequently avoid, flowers they have recently emptied. We have also found that, although these birds can learn color-reward associations, when revisiting flowers they pay more attention to the spatial location of the flowers. When flowers are close together, the birds learn flower locations with respect to other nearby flowers. They also learn faster which flowers are rewarded if these flowers are next to each other. When flowers are further apart (>40 cm), however, their locations are encoded relative to landmarks outside of the array. Once the location of a flower has been learned, birds are apparently oblivious to changes in its color pattern. These birds also pay attention to whether they have seen flowers previously, preferring to visit new flowers before those they have seen and not visited. Not only can these birds remember what they have fed from and where, they may also be able to remember when they visited. We do not know yet how well matched their timing abilities are to relevant flower-refilling rates.
Territorial female northern harriers, Circus cyaneus, often evicted species of intruding raptors larger than themselves from their territories, but never species smaller than themselves. Contrary to the hypothesis that aggressive responses serve primarily to reduce exploitative competition, responses by harriers to larger raptor species seldom occurred during hunts by these intruders. Howerer, harriers responded frequently to larger raptor species when these species intruded while harriers were actively hunting, supporting the hypothesis that aggressive responses serve primarily to reduce interference competition in the form of kleptoparasitism of harriers' prey by larger raptor species. The lack of defence by harriers against smaller intruding raptor species apparently resulted from harriers' abilities to kleptoparasitize these intruders. Hence, whether or not a territorial harrier responded aggressively to an intruding raptor species depended on the size of the harrier relative to the size of the intruder, which in turn influenced its ability to kleptoparasitize or to be kleptoparasitized.
Ruby-throated hummingbird Archilochus colubris has the most extensive breeding distribution of any hummingbird species in North America. In its most northern distribution in Canada, its spring arrival often occurs before herbaceous flowers are in bloom, and in many parts of its range it breeds in habitats where floral nectar is scarce or unavailable. Evidence supports the hypothesis that the dates of spring arrival and northern breeding distribution of the rubythroat, and probably the rufous hummingbird Selasphorus rufus, are determined by a commensal relationship with yellow-bellied sapsucker Sphyrapicus varius, in which the principal energy source for the hummingbirds is sucrose in sap from trees drilled by the sapsuckers. -Authors
Understanding how home range size varies across seasons can provide insights into how birds respond to changes in resource levels. Yet, seasonal variation in home range size of most Neotropical birds is poorly understood. We recorded locations of color-banded Tropical Kingbirds during four years at a site comprised of cerrado woodland, humid forest, and cattle pasture in the southern Amazon Basin. We found no significant difference in the mean home range size of males (43.0 ± 22.6 ha) and females (45.6 ± 45.5 ha). Although kingbirds had smaller home ranges in the non-breeding season than
in the breeding season, differences in home range size were not significant between seasons. We radiotracked nine kingbirds and compared their home range size to that of color-banded birds without radio transmitters. We found no significant difference in the mean home range size of kingbirds determined by telemetry data (41.8 ± 24.0 ha) and those determined by observations of color-banded individuals (43.4 ± 36.3 ha), suggesting that both methods of estimating home range size are roughly equivalent.
We observed 26 male Rufous Hummingbirds (Selasphorus rufus) on their breeding territories to quantify display behaviors and to interpret their functions. Territory holders responded to intruding conspecific males with aggressive chases until the intruder left the territory. Female intruders received dive displays and shuttle-flights, which we interpret as courtship behavior. Dive displays were J-shaped (concave upward) in both ascent and descent, contrary to other reports of oval-shaped displays. We present a representative sonogram of the sounds produced during these dive displays. Función de los Despliegues de los Selasphorus rufus Machos Resumen. Observamos 26 Selasphorus rufus machos en sus territorios de reproducción para cuantificar sus comportamientos de despliegue e interpretar las funciones de éstos. Los dueños de los territorios respondieron a intrusiones de machos coespecíficos con persecuciones agresivas hasta que los intrusos abandonaron el territorio. Por su parte, las hembras intrusas recibieron despliegues en picada y patrones de vuelo repetidos, los cuales interpretamos como comportamientos de cortejo. Los despliegues en picada tuvieron forma de J (cóncava hacia arriba) tanto en ascenso como en descenso a diferencia de reportes previos sobre despliegues en forma de óvalo. Adicionalmente presentamos un sonograma representativo de los sonidos producidos durante los despliegues en picada.
In contrast to vocalizations, nonvocal avian sounds have received little attention as potential means of communication. The high wing-beat frequency of hummingbirds in concert with the modified flight feathers of some species, generate sounds with the potential to play a role in communication. Technological limitations of previous studies have compromised assessment of the acoustic characteristics and importance of these sounds. This study was designed to record and analyze the sex-specific wing sounds of four hummingbird species, in order to provide a framework for further communication studies. We collected digital recordings of hummingbirds during hover flight and analyzed these with computer-based sound software. Our results showed that (1) males of all four species had higher wing-beat frequencies than conspecific females; (2) there was greater intra- and interindividual variation in wing-beat frequency than previously documented; (3) though not specifically tested, the sexual dimorphism and interspecific differences in wing-beat frequency support previous findings that wing-beat frequency is inversely related to wing length; and (4) that digital sound analysis is a powerful new tool for detailed study of wing sounds. We provide the first description of a characteristic behavior, which we have called the ‘Cobra’, in which an individual dramatically increases its wing-beat frequency. Finally, we have significantly expanded understanding of the wing trill sound produced by the modified outer primary feathers, and have shown that female Black-chinned Hummingbirds (Archilochus alexandri) also produce wing trill components despite previous beliefs that these were unique to male hummingbirds. Características de los Sonidos de las Alas de Cuatro Especies de Picaflores que Crían en Canadá Resumen. A diferencia de las vocalizaciones, los sonidos no-vocales de las aves han recibido poca atención como medios potenciales de comunicación. Las altas frecuencias de aleteo de los picaflores, en conjunto con las plumas modificadas para el vuelo de algunas especies, generan sonidos que tienen el potencial de jugar un rol en la comunicación. Las limitaciones tecnológicas de los estudios previos han dificultado la evaluación de las características acústicas y de la importancia de estos sonidos. Este estudio fue diseñado para grabar y analizar los sonidos de las alas específicos de cada sexo en cuatro especies de picaflores con el objetivo de sentar las bases para futuros estudios de comunicación. Colectamos grabaciones digitales de picaflores durante el vuelo suspendido y las analizamos en computadoras con programas de sonido. Nuestros resultados mostraron que: (1) los machos de las cuatro especies tuvieron frecuencias de aleteo más altas que las hembras coespecíficas; (2) existió variación intra- e inter-individual en la frecuencia de aleteo mayor que la documentada previamente; (3) aunque no fue evaluado específicamente, el dimorfismo sexual y las diferencias inter-específicas en la frecuencia de aleteo apoyan hallazgos anteriores que relacionan inversamente la frecuencia de aleteo con la longitud de las alas; y (4) que el análisis digital de los sonidos es una nueva herramienta de gran utilidad para el estudio detallado de los sonidos de las alas. También brindamos la primera descripción de un comportamiento característico que nosotros llamamos ‘Cobra’, en el cual un individuo aumenta dramáticamente la frecuencia de aleteo. Finalmente, hemos incrementado de modo significativo el conocimiento del sonido producido por las plumas primarias externas modificadas y hemos mostrado que las hembras de Archilochus alexandri también producen sonidos con las alas, a pesar de que anteriormente se creía que éstos eran exclusivos de los picaflores machos.
Most studies of territoriality in hummingbirds have focused on intraspecific competition for resources and the consequences for the spatial distribution of individuals within a habitat. As a result, we know little of the effects of interspecific competition for resources and less still of temporal resource partitioning. Here I describe the interactions of four species of tropical hummingbird which defended the same territory at different stages in the flowering period and at different times of the day. The pattern of territory defence was greatly influenced by the dominance hierarchy between species and the costs and benefits of territory ownership. I used a simple economic model to calculate the predicted territory size based on four potential strategies. Hummingbirds appeared to be defending territories of the smallest economical size, agreeing with two hypotheses: (1) that hummingbirds minimize the cost of territory ownership and (2) that hummingbirds maximize the time spent sitting. The model predicted accurately the observed pattern of territory acquisition; hummingbirds initiated defence as soon as the territory contained sufficient resources and were either displaced by a larger species or replaced by a smaller one as the value of the territory changed.
Thirteen territorial male Anna's Hummingbirds, Calypte anna, were observed during the 1981 and 1982 breeding seasons. Breeding territories were large, but size was not determined by energy availability. When a food source (sucrose solution in feeders) was present, the degree to which it was defended was a function of food quality. If a high-quality food source was absent, males did not exhibit the behaviors associated with defending a food source, but breeding territoriality remained intact. Territories were maintained for the entire breeding season even when food quality was varied. The lack of a relationship between the number of chases involving females and dive displays with variations in food quality, along with observations of long territory tenure, suggest that the primary function of the territory is reproductive and that an internal food source is not necessary for its maintenance.
Time spent in territorial defense was measured during territory establishment for non-breeding Black-chinned (Archilochus alexandri) and Anna's (Calypte anna) hummingbirds. Newly established territory holders spent more time chasing intruders than neighboring established owners, which served as controls. This higher investment in defense by the new owners was due to 1) a longer time spent per each chase and 2) in some cases, a higher frequency of chases at the onset of territory ownership.
Vita. Thesis (M. Sc.)--University of British Columbia, 1986. Bibliography: leaves 100-108.
Feeding territories of Golden-winged Sunbirds contain enough energy to sup- port an individual's daily energy requirements, and the amount of nectar per flower inside a territory tends to average higher than in adjacent undefended flowers. When undefended nectar levels are low (especially below 2 /ul per flower) the costs of territorial defense can easily be offset by energy saved from shortened foraging time budgets made possible by feeding at the higher average nectar levels. At higher undefended nectar levels the costs of territorial defense should not be recoverable. The balance between these costs and gains appears to define the conditions when territorial defense in this species is advantageous.
Science Citation Classic Award Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by menas of mathematical models. These models are very similar, in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) - usually energy - and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e. optimal diet); (2) choice of which patch type to feed in (i.e. optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test such predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will require much modification, especially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated than just energy.
A system of compensating phenological responses of different species to unusual rainfall conditions may play a major role
in maintaining an orderly, staggered sequence of flowering peaks among the hummingbird-pollinated plants of a Costa Rican
rain forest. Quantitative phenological studies over several years may be essential to understanding the temporal organization
of many tropical communities.
( l) Within areas, the size of individual territories of red grouse varied inversely with the proportion of ground occupied by vegetation containing the birds' main food plant, heather. This apparent adjustment was most obvious where the heather was sparse and heavily grazed by sheep and cattle.
(2) The smallest territories, and therefore the densest breeding stocks, tended to occur where the heather sward was broken up into numerous small patches (whether as a result of burning or otherwise), with a large length of heather-patch edge per hectare.
(3) Territory size was not related to the yield of green shoots per hectare of heather on the territories in spring.
(4) Territories of cocks paired with hens were larger than those of cocks with no hens. As territories did not differ in the productiveness of their heather in spring, those belonging to mated cocks contained most green shoots.
(5) The number of young reared by individual pairs was not related to the total weight of green heather shoots on their territories in spring or to the mean yield of shoots per hectare.
We examined the relationship between time budgeting for major activities of nectar-feeding birds and the foraging efficiency (total energy intake divided by total energy spent foraging) required to maintain an energetically balanced, 24-h energy budget. The hyperbolic shape of the curve relating this @`required foraging efficiency@' to percent time foraging (percent of daylight hours) suggests that at low percent times for foraging a major change in foraging efficiency would be required to decrease substantially the time for feeding, whereas at low foraging efficiency small changes in foraging efficiency would produce major changes in time budgeting for foraging. For hummingbirds, which usually hover while foraging, and for sunbirds, which usually perch while foraging the required foraging efficiency increased at a given percent time for foraging with (1) decreasing body size, (2) decreasing day length, (3) lower average temperatures, and (4) increasing nonfeeding flying time (such as for feeding young and territorial defense). The sunbirds would require a higher foraging efficiency (all other conditions being equal) than hummingbirds because of their lower foraging costs per unit time. However, the generally lower extraction efficiency of hummingbirds, due to their higher costs for feeding, tends to balance their lower required foraging efficiency, resulting in foraging time budgets similar to those for sunbirds. Actual foraging efficiency of these nectar-feeding birds is an increasing function of energy available per flower. The asymptotic relationship of empirical measures of this @`achieved foraging efficiency@' and nectar volume obtained per flower derives from a combination of coast and benefit terms relating to (1) rate of energy extraction per flower, and (2) time spent not probing flowers on a foraging bout. This relationship suggests that at low initial nectar volumes substantially more foraging efficiency results from slight increases in average nectar volumes per flower, whereas at high initial volumes virtually no change occurs in foraging efficiency with similar nectar availability changes. Thus, slight increases of nectar availability per flower should produce no obvious change in percent-time foraging at high initial volumes, but a marked decrease in percent-time foraging at low initial volumes. Similarly, the benefits achieved from an equivalent increase in average nectar volumes per flower through additional defense costs are proportionately higher and increase faster at low initial volumes than at high initial volumes. The general concept of foraging efficiency, or profitability, seems to be an important component of theories dealing with prey selection, especially in relation to foraging time.
The hummingbirds of California exist in two contrasting states of dispersion which alternate during the course of a year. The birds are dispersed over wide areas during the northward migration and the spring breeding season, but in the postbreeding season and on their southward migration they tend to congregate in the higher mountains. The distribution patterns of hummingbird-pollinated plant species in California are shown to be correlated with these two phases of hummingbird dispersion. Winter- and spring-blooming plant species are distributed over extensive areas of low to intermediate elevation and are largely allopatric, while summer-blooming plant species in the high mountains commonly occur in sympatric flocks. The species flocks of hummingbird flowers in the high mountains are explained as a consequence of the dense summer aggregations of hummingbirds. The latter provide a pool of potential pollinators for plant species normally pollinated by other agents and promote the divergence of local races and species adapted for hummingbird pollination.
Their territory holding, coupled with a number of other important features of the rufous hummingbird, has allowed us to investigate the cognitive abilities of these animals in the field. These birds can remember, so as to subsequently avoid, flowers they have recently emptied. We have also found that, although these birds can learn color-reward associations, when revisiting flowers they pay more attention to the spatial location of the flowers. When flowers are close together, the birds learn flower locations with respect to other nearby flowers. They also learn faster which flowers are rewarded if these flowers are next to each other. When flowers are further apart (>40 cm), however, their locations are encoded relative to landmarks outside of the array. Once the location of a flower has been learned, birds are apparently oblivious to changes in its color pattern. These birds also pay attention to whether they have seen flowers previously, preferring to visit new flowers before those they have seen and not visited. Not only can these birds remember what they have fed from and where, they may also be able to remember when they visited. We do not know yet how well matched their timing abilities are to relevant flower-refilling rates.
This field study of female and immature migratory rufous hummingbirds (Selasphorus rufus) reveals that their feeding territories are closely regulated in size to maintain environmental reserves of energy per individual. Columbine (Aquilegia formosa) produces nectar about four times as fast per nectary as Indian paintbrush (Castilleja miniata) but territories have similar daily caloric productivity regardless of their floral species composition.Une etude en nature de femelles et d'oisilons du colibri migrateur Selasphorus rufus demontre que les territoires ou ils se nourrissent sont delimites de facon a ce qu'il y ait dans le milieu une reserve constante d'energie par individu. L'ancolie (Aquilegia formosa) produit son nectar environ quatre fois plus vite par nectaire que la castillejie Castilleja miniata, mais les territoires ont des productivites caloriques quotidiennes semblables, quelle que soit la composition de la population florale.[Traduit par le journal]
Three nectar-eater systems differ in the degree and consistency with which nectar is limiting to the birds. A gradient of nectar limitation exists, ranging from no limitation to limitation some years but not others, to apparent limitation most of the time. The ecological and evolutionary effects of different limitation regimes on aggression and tcrritoriality, on resource partitioning and avian community structure, and on plant pollination strategies are discussed.
Territorial female northern harriers, Circus cyaneus, often evicted species of intruding raptors larger than themselves from their territories, but never species smaller than themselves. Contrary to the hypothesis that aggressive responses serve primarily to reduce exploitative competition, responses by harriers to larger raptor species seldom occurred during hunts by these intruders. Howerer, harriers responded frequently to larger raptor species when these species intruded while harriers were actively hunting, supporting the hypothesis that aggressive responses serve primarily to reduce interference competition in the form of kleptoparasitism of harriers' prey by larger raptor species. The lack of defence by harriers against smaller intruding raptor species apparently resulted from harriers' abilities to kleptoparasitize these intruders. Hence, whether or not a territorial harrier responded aggressively to an intruding raptor species depended on the size of the harrier relative to the size of the intruder, which in turn influenced its ability to kleptoparasitize or to be kleptoparasitized.
Species with similar floral structures and with similar flowering periods and time of pollen and nectar presentation may compete for the service of the same pollinators. The outcome of interspecific competition was analyzed with a simple two-species model. The reproductive success of a species depends on its relative frequency. The minority species will be at a reproductive handicap because it suffers a larger percentage of heterospecific pollinations. The reproductive handicap of the minority species leads to a smaller standing crop in the next generation, which in turn enhances the minority disadvantage. This should lead to rapid exclusion of the minority species from the immediate flora. An increase in pollinator constancy to a given plant species retards the elimination of the rarer species. Pollinator preference for a given plant species may enhance or retard this progression depending on whether the minority species is preferred, since preference alters the effective frequencies of the two species. ...
Six species of hummingbird breed in mainland California, but only the Anna's Hummingbird (Calypte anna) remains year-round in the vicinity of its breeding habitat. However, on some of the Channel Islands, particularly Santa Cruz and Santa Catalina, and on the island-like Palos Verdes Peninsula, Anna's and the insular race of the Allen's Hummingbird (Selusphorus susin sedentarius) are both resident year-round. Temperate zone hummingbirds, when not separated by habitat differences, generally defend territories between, as well as within, species (Pitelka 1951, Legg and Pitelka 1956, Cody 1968)) presumably the result of their specialized and relatively similar feeding behavior. Grant (1966) has suggested that ecologically similar species do not generally occur together in insular situations. On the large, habitat-diverse islands of the West Indies, Lack (1971) reported that hummingbirds were separated most frequently by habitat. Whenever Lack found 2 species of hummingbirds using the same habitat, they were different in body size (as measured by wing and/or culmen length), indicating to him that the species were occupying different ecological niches. For example, the larger member of a sympatric pair of hummingbirds had on the average 1.55 times longer wings and 2.08 times longer culmen than the smaller member (Lack 1971: 230). It is therefore interesting that 2 relatively similarly-sized species of hummingbird (Anna's Hummingbird has 1.22 times longer wings and 1.05 times smaller culmen than the resident race of Allen's Hummingbird) should be resident year-round on the Channel Islands. This paper examines the resource use of Anna and Allen hummingbirds on Santa Cruz Island, to determine how these species coexist between Sep- tember and early November. This period is deemed critical for the continued existence of the 2 hummingbirds because only 2 native plants, California fuchsia species Zauschneria culifornicu and 2. cam, are flowering on the island. These food plants are not abundant and are found only infrequently in dense concentrations, so both species of hummingbirds aggregate in the bottoms of canyons and washes to feed on Zauschneriu nectar. Also during this period of the year on Santa Cruz Island, insect availability reaches its lowest level (Yeaton 1972)) presumably due to the previous 3 months in which there is no rain. During the remainder of the year the hummingbirds are separated by habitat on Santa Cruz Island. Allen's are found in the denser and taller chaparral of the north-facing slopes and in riparian woodlands,
Postbreeding migratory female and immature rufous hummingbirds (Selasphorus rufus) establish feeding territories in dense meadows of several 'typical hummingbird plant species' and in individual Rhamnus purshiana shrubs. Resource utilization patterns and activity budgets of individuals in meadows are typical of territorial hummingbirds. Individuals in Rhamnus forage a high proportion of the time and are absent from their territories frequently and for long durations early and late in the day, and feed on other species during these absences. Rhamnus is marginally profitable to feed on and defend, but it may be the only available habitat for the individuals that utilize it.
A number of regression situations in fish and fishery biology are examined, in which both of the variates are subject to error of measurement, or inherent variability, or both. For most of these situations a functional regression line is more suitable than the ordinary predictive regressions that have usually been employed, so that many estimates now in use are in some degree biased. Examples are (1) estimation of the exponent in the weight:length relationship, where almost all published values are somewhat too small; and (2) estimating the regression of logarithm of metabolic rate on log body weight of fish, where the best average figure proves to be 0.85 rather than 0.80. In the very common situation where the distribution of the variates is non-normal and open-ended, a functional regression is the most appropriate one even for purposes of prediction. Two ways of estimating the functional regression are (1) from arithmetic means of segments of the distribution, when computed symmetrically; and (2) from the geometric mean of one predictive regression and the reciprocal of the other. The GM regression gives a more accurate estimate when it is applicable; it is appropriate in all situations where the variability is mainly inherent in the material (little of it due to errors of measurement), or where the measurement variances are approximately proportional to the total variance of each variate; and it is the best estimate available for short series with moderate or large variability even when neither of these conditions applies. When error in X results solely from the measuring process the predictive regression of Y on X is also the functional regression if observations of X are not taken at random but rather have pre-established values, as is usual in experimental work. The uses of the various regressions are summarized in Table 8.
The simultaneous flowering of co—occurring plant species with similar pollinator affinities may result in interspecific pollen transfer and consequent fecundity reductions due to wastage of pollen, stigma surfaces, and effective pollinator visits. In such cases competition for pollination occurs and may lead to or maintain sequential flowering. Two common perennials in the mountains of west—central Colorado, Delphinium nelsoni and Ipomopsis aggregata, flower sequentially in the same meadows and are visited commonly by Broad—tailed Hummingbirds (Selasphorus platycercus). Hummingbirds carry pollen of both species and their exclusion from flowers leads to significant seed set reductions. During the brief period of flowering overlap between D. nelsoni and I. aggregata in natural meadows, hummingbirds visit both species, carry mixtures of their pollen, and appear to cause interspecific pollen transfer. Flowers of both species receptive during this period suffer significant seed set reductions relative to those receptive during nonoverlap periods. Interspecific pollinator flights and pollen transfer also occur in mixtures of potted plants, and seed set reductions consistently occur for both D. nelsoni and I. aggregata in such mixtures relative to single—species controls. Finally, seed set reductions occur for both species following interspecific hand pollination of potted plants. Fecundity reductions in natural and synthetic mixtures of D. nelsoni and I. aggregata indicate that the 2 species compete for hummingbird pollination and suggest that the competitive interaction involves interspecific pollen transfer. The observed reproductive effects represent a selective force sufficient to maintain divergent flowering times of D. nelsoni and I. aggregata in nature.
This paper describes an investigation into whether or not spring territorial behavior was limiting the breeding density of a population of Great Tits on Wytham Estate, near Oxford. The analysis of distances between neighboring nests showed that nest sites were more spaced out than would be expected from a random distribution; this indicated that interactions between the birds produced at least a local density-limiting effect. In 2 successive years, established territorial pairs were removed from a stable spring population in mixed woodland. The removed birds were rapidly replaced by new pairs. These newcomers were largely first-year birds; they came from territories in the hedgerows that surrounded the wood; the vacated hedgerow territories were not refilled. The hedgerows were found to be suboptimal in terms of reproductive success. Thus territory limited the breeding density in the optimal habitat. Song advertisement is probably important in maintaining territorial boundaries, hedgerow birds being able to detect the presence of individual woodland territory holders by recognizing their songs. The effect of winter food supply on the population was investigated by supplying excess food throughout one winter. This artificial food supplement appeared to have no effect on the number of Great Tits breeding in the wood, but did produce an increase in the case of a related species, the Blue Tit. The results show that territorial behavior influences density; this is not considered to be a function of territory in the evolutionary sense, but rather a consequence of spacing out that has been selected for in some other context. A possible advantage of spacing out in the Great Tit is as a defense against predators. Territory size varies considerably from year to year. These variations are the result of interactions between the birds themselves, rather than direct adjustments of territory size to fluctuations in some environmental resource. Even though territory has an effect on the number of birds breeding in the wood,it is not an important density-dependent factor acting to regulate the population.
Most studies of territoriality in hummingbirds have focused on intraspecific competition for resources and the consequences for the spatial distribution of individuals within a habitat. As a result, we know little of the effects of interspecific competition for resources and less still of temporal resource partitioning. Here I describe the interactions of four species of tropical hummingbird which defended the same territory at different stages in the flowering period and at different times of the day. The pattern of territory defence was greatly influenced by the dominance hierarchy between species and the costs and benefits of territory ownership. I used a simple economic model to calculate the predicted territory size based on four potential strategies. Hummingbirds appeared to be defending territories of the smallest economical size, agreeing with two hypotheses: (1) that hummingbirds minimize the cost of territory ownership and (2) that hummingbirds maximize the time spent sitting. The model predicted accurately the observed pattern of territory acquisition; hummingbirds initiated defence as soon as the territory contained sufficient resources and were either displaced by a larger species or replaced by a smaller one as the value of the territory changed.
In polygynous birds, bright plumage is typically more extensive in the sexually competitive males and develops at or after sexual maturity. These patterns, coupled with the importance of male plumage in sexual displays, fostered the traditional hypothesis that bright plumages and sexual dichromatism develop through the actions of sexual selection on males. This view remains problematic for hummingbirds, all of which are polygynous, because their bright iridescent plumages are also important non-sexual signals associated with dominance at floral nectar sources. Here I show that female amethyst-throated sunangels [Heliangelus amethysticollis (d'Orbigny & Lafresnaye)], moult from an immature plumage with an iridescent gorget to an adult plumage with a non-iridescent gorget. This ‘reversed’ ontogeny contradicts the notion that iridescent plumage has a sexual function because sexual selection in polygynous birds should be lowest among non-reproductive immature females. Moreover, loss of iridescent plumage in adult females indicates that adult sexual dichromatism in H. amethysticollis is due in large part to changes in female ontogeny. I suggest that both the ontogeny and sexual dichromatism evolved in response to competition for nectar.
HAT are the conditions which facilitate or hinder the evolution of ter- ritoriality? No generally accepted solution to this problem has yet been found-perhaps because too specific an answer has been sought for too general a question. Instead, the diversity of systems of territorial and other aggressive behavior has come to be well appreciated, as evidenced in recent reviews of territoriality (e.g., Kuroda, 1960; Carpenter, 1953; Hinde, 1956), and the impossibility of providin g a specific answer applicable to all types of territoriality is now realized. Arguments over which are the primary selection pressures leading to cer- tain types of territoriality continue, however, as shown in the recent contribu- tions bearing on the "function" of territoriality by Stenger (1958)) Wynne- Edwards (1962), Kalela (1958)) Kuroda (1960), Peters (1962)) and others. The present paper offers a new orientation to the problem by presenting a general theory for the evolution of territoriality with special reference to its diversity among species. Since most of the previous theories have already been shown to be untenable or severely limited (see especially Carpenter, 1958; Tinbergen, 1957; and Hinde, 1956, for criticism of them), little attention will be given to them here. A theoretical framework for the consideration of some of the mechanisms promoting and limiting the evolution of territorial behavior is outlined in Fig. 1. Aggressive behavior is generally employed by individuals in the acquisition of goals which tend to maximize individual survival and reproduction. Natu- ral selection should favor aggressive behavior within a population when these goals are consistently and easily accessible to individuals through aggression but should not favor it when they are not accessible. For example, when a food supply cannot be feasibly defended, because of its mobility or transient nature , generally no territorial system is evolved to defend it; and the terri- tory, if present, may be restricted only to the nest and the area reachable by the parents on the nest. Such cases are found in colonial sea birds, nomadic and social feeding passerine species, and aerial feeders. In these species the goal of increased or guaranteed food supply is unlikely to be attained through aggression. On the other hand, if the individual depends for its nesting requirements,
It is proposed that natural selection favors individuals that defend territories larger than necessary to include resources just sufficient for survival and/or reproduction. These are referred to as super territories. Defense of a disproportionate share of space/resources by more aggressive individuals reduces the possibility of survival and/or reproduction of less aggressive conspecifics. The effect is to increase the relative contribution to future gene pools of individuals capable of defending territories in optimum habitat. Alternative hypotheses are compared, and ways are suggested to distinguish among them. Available empirical evidence seems to fit the present hypothesis better than other commonly held explanations of the adaptive function of territoriality, and the hypothesis provides a reasonable explanation for the evolution not only of breeding territories but of winter territories among resident as well as migratory species.
Territorial behavior of Broad-tailed ( Selasphorous platycercus ) and Rufous ( Selasphorous rufus ) hummingbirds in Colorado was measured at sites with feeders containing10%, 20%, and 30% sucrose solutions, respectively. The presence or absence of territory holders, number of intruders, and intensity of defense were measured at the three levels of energy availability. Migrating Rufous Hummingbirds displaced Broad-tailed Hummingbirds from territories they had defended during the breeding season; Broad-tailed Hummingbirds then defended only lower quality sites. Both Broad-tailed and Rufous hummingbirds employed more energetically expensive behaviors when defending high quality sites, with longer chases more often supplemented with chip calls and hovering. Other investigators have suggested that chip calls and hovering are precursors to a chase. However, I found that chasing was the default response to the presence of an intruder. Chip calls and hovering were added to intensify a chase. In the few cases where chip calls were uttered or hovering occurred without a chase, Rufous Hummingbirds were more likely to exhibit this behavior than Broad-tailed Hummingbirds.
Cooperatively breeding groups may be constrained in size by the territory available to them, or territories may be expanded to accommodate extra group members. Here, we show that there was no relationship between the number of adult green woodhoopoes Phoeniculus purpureus in a group and the size of its territory. Furthermore, territories were remarkably stable between seasons, with no significant changes in area, despite fluctuating group sizes. These results suggest that food was not limiting at the group sizes found in this study: sufficient resources were available within existing territories for groups that were expanding in size. Following an increase in group membership, a larger proportion of the available area was utilised. Groups also used a larger area in the non-breeding season compared to when breeding: in the latter instance, foraging was concentrated in the vicinity of the nest.
This example is provided so that non-theorists may see actual applications of the theory previously described. The Dickcissel sex ratio is employed as an indirect index of suitability. A sex ratio index was found to be correlated positively with density. This is consistent with the hypothesis that territorial behavior in the males of this species limits their density. This study provides a valid example of how the problem can be approached and offers a first step in the eventual identification of the role of territorial behavior in the habitat distribution of a common species.
Territorial activity in the Anna hummingbird (Calypte anna) was measured while energy availability on the territory was varied. On days when energy availability was unlimited, residents defended highly exclusive territories primarily by energetically expensive defense behaviors. As energy availability decreased, exclusiveness declined gradually, relative use of energetically inexpensive defense increased, and owners spent less time on the territory.Territorial behavior also varied with short term depressions in energy availability: A lower percentage of intruders was chased and departures of an owner from its territory were more frequent shortly after feeding.When resource dispersion was increased without changing substantially total rewards per territory, chasing by owners increased.
By analysis of time budgets the daily energy expenditure in territorial individuals of a Hawaiian honeycreeper (Vestiaria coccinea, Fam. Drepanididae) were estimated during the nonbreeding season and compared to that of nonterritorial individuals. The mean rise in living costs was 2.3 kcal/24 h or 17% of the nonterritorial energy budget. The most costly territorial behavior was advertisement rather than chasing, and total territorial cost was seen to be little affected by the number of intruders or the size of the territory. These results are compared with data on feeding (nonbreeding) territories of other nectar-feeding birds. The suggestion is made that hummingbirds may be more likely to develop nonbreeding territorial behavior in any set of environmental circumstances than are honeycreepers because of relatively lower total cost of advertisement plus chasing.
There was no difference in home range size between supplementally fed and unfed lizards even though supplementally fed lizards gained significantly more body mass than did unfed lizards. A logistic growth model was fit to curves of accumulative home range size against days of observation for fed and unfed lizards. An analysis of these curves showed that supplementally fed lizards's home range estimates grew at a slower rate than did unfed lizards. Thus, fed lizards utilized the habitat at a slower rate than did unfed lizards. Moreover, the rate at which fed lizards utilized the habitat was linearly related to their increase in body mass. Supplementally fed male and unfed lizards of both sexes were equally active through the summer. On average, they were active on one out of every two days (49.4%), whereas, supplementally fed females were active on a significantly greater number of days (83.9%).
Migrant Rufous Hummingbirds (Selasphorus rufus) arrive in eastern Arizona in late summer and establish feeding territories from which other hummingbirds are excluded. Territories vary 100-fold in area and 5-fold in number of flowers. A simple cost-benefit model accounts for observed variation in territory size and number of flowers defended. Both sexes defend territories, but \male \male utilize denser flowers than \female \female. These differences appear to be related to sexual dimorphism in wing disc loading. Selasphorus rufus appears to have sacrificed efficient flight for aggressive ability as a strategy for competing with resident hummingbird species during its migration. Comparison of feeding territories of S. rufus and other nectarivorous birds indicate similarities which suggest that these systems may be subject to similar economic constraints.
Thesis (D. Phil.)--McGill University, Montreal, Quebec, 1979. Includes bibliographical references.
An energy-based model of feeding territoriality is described. The model predicts an optimal territory size where the territory holder's net energy intake is maximized, on a daily or seasonal time scale. Simulated effects on optimal territory size of animal size, food availability, and competitor density are in general agreement with observed relationships in a wide variety of animals. When salmonid data are used to estimate the model parameter values, predicted territory sizes are similar to those actually observed. When emigration is allowed, the model predicts that territoriality, through individual selection alone, can regulate population size, but that this regulation breaks down when initial densities exceed some threshold value. Sensitivity analysis shows optimal territory size to be most affected by those parameters influencing food intake and energy expenditure. Some alternative criteria for optimization are also discussed. An animal maximizing net foraging efficiency has a smaller territory than one maximizing net energy, but the effects of animal size, food availability, and competitor density on territory size are the same in either case.
A concept is developed for the regulation of populations by density-dependent movement, rather than by overt competition alone. Fitness is seen as maximising the reproductive advantage of a balance between migratory and congregatory behaviours. Population density is shown to be spatially, as well as temporally dynamic and a mechanism is proposed that accounts for observed spatial behaviour.
A model is proposed predicting that in nectarivorous birds territorial behavior will occur above a lower threshold of nectar
productivity in a foraging area and disappear above an upper threshold. These thresholds are determined by the daily costs
of living of territorial and of nonterritorial individuals and by the pressure of competing birds for the resource. Decline
of efficiency of territorial exclusiveness is predicted as productivity increases from the lower to the upper threshold. Hawaiian
honeycreepers (Vestiaria coccinea) supported the model.
Territorial behavior in fall migrant rufous hummingbirds
- K B Armitage
ARMITAGE, K. B. 1955. Territorial behavior in fall migrant rufous hummingbirds. Condor, 57: 239-240.
An energy-based model of optimal feeding territory size Migration: orientation and navigation Downloaded from www.nrcresearchpress.com by Depository Services Program on 06/06/13 For personal use only
- L M Dill
DILL, L. M. 1978. An energy-based model of optimal feeding territory size. Theor. Popul. Biol. 14. In press. EMLEN. S. T. 1975. Migration: orientation and navigation. In Can. J. Zool. Downloaded from www.nrcresearchpress.com by Depository Services Program on 06/06/13 For personal use only. Avian biology. Vol. 5. Edited by D. S. Farnerand J. R. King. pp. 77-128.