Article

Nest sites as limiting resources for cavity-nesting birds in mature forest ecosystems: A review of the evidence

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Abstract

Assumptions that populations of cavity-nesting birds are limited by access to nest sites have largely been based on anecdotal reports or correlative data. Nest-box-addition experiments or tree-cavity-blocking experiments are potentially rigorous ways to investigate how densities of breeding birds are affected by access to nest cavities. Experimental evidence indicates that natural tree holes are limited in human-altered landscapes, but the possibility that cavity nests are limited in old growth (unmanaged) forests is less clear. I reviewed 31 nest-cavity-removal or addition experiments conducted with 20 species of cavity-nesting birds in mature forests. Of these 31 experiments conducted with a variety of different species of birds, only 19% reported statistically significant changes in breeding densities. However, none of these studies included data about the reproductive history of individuals colonizing the boxes (i.e., whether birds using the boxes would have otherwise been floaters or that birds excluded from blocked cavities on the plots did not simply move elsewhere), so they provided no strong evidence that the number of breeding pairs was limited by availability of nest sites at the population scale. Although some studies indicate that nest sites are limited at local (plot) scales in old growth forests, there is still little empirical evidence for nest-site limitation at the population-and landscape-level in mature, unmanaged forests. I review the challenges in designing and interpreting box-addition experiments and highlight the main gaps in knowledge that should be targeted in the future.

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... It has generally been argued that nest site availability limits the population and the reproduction of cavity-nesting birds (von Haartman, 1957;Newton, 1994), particularly in secondary cavitynesting birds (Cody, 1985;Miller, 2010;Wiebe, 2011). Secondary cavity nesters, unlike other types of cavity nesters, do not excavate nests and rely on existing cavities, which makes them more likely to suffer from nest site limitation (Newton, 1994;Wiebe, 2011) and face inter-or intraspecific competition for the primary breeding resource (tree cavities). ...
... It has generally been argued that nest site availability limits the population and the reproduction of cavity-nesting birds (von Haartman, 1957;Newton, 1994), particularly in secondary cavitynesting birds (Cody, 1985;Miller, 2010;Wiebe, 2011). Secondary cavity nesters, unlike other types of cavity nesters, do not excavate nests and rely on existing cavities, which makes them more likely to suffer from nest site limitation (Newton, 1994;Wiebe, 2011) and face inter-or intraspecific competition for the primary breeding resource (tree cavities). Although high nest site availability can locally increase breeding densities in many bird species (Aitken & Martin, 2008;Cockle, Martin, & Drever, 2010;Enemar & Sj€ ostrand, 1972;S en echal, Gauthier, & Savard, 2008), there is no evidence for an influence on brood sex ratio. ...
... Nest site availability is the primary factor limiting the reproduction of secondary cavity-nesting birds (Miller, 2010;Newton, 1994;Wiebe, 2011), with great tits favouring male offspring in the area with abundant nest sites. To our knowledge, no study has previously investigated this pattern of sex allocation in birds. ...
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Sex allocation theory as applied to local resource competition (LRC) predicts that parents should skew investment towards philopatric offspring when local resources are abundant. Alternatively, parents should allocate resources to the dispersing sex when local resources are deficient in order to limit competition among relatives. Nest sites have been shown to be the primary factor limiting populations of secondary cavity-nesting birds. In this study, we manipulated nestbox density to test its effect on the sex allocation patterns of the great tit, Parus major, a species in which female offspring are more likely to disperse than male offspring. We also investigated the relationship between the brood sex ratio and the time of breeding, which has been shown in many studies to influence sex allocation. Consistent with the LRC prediction, parents invested more in male offspring and produced a male-biased sex ratio in the area where nestboxes were abundant. In our study, the reproductive success of great tits declined as the season progressed; however, the time of breeding had no effect on the sex ratio of the offspring. Overall, the results of our study suggest that nestbox availability can influence sex allocation in great tits, and may also represent a relatively common phenomenon in other secondary cavity-nesting birds.
... There is strong evidence which supports this limitation in managed forest, but less evidence for such limitation in unmanaged and old growth forests (Newton, 1998). Only 19% of the studies which assess limitation in old growth forests have reported significant changes in density of cavity-nesters (Wiebe, 2011). Hence, the conclusions from experiments carried out in mature forests appear less consistent (Cornelius et al., 2008). ...
... Within these, six were recently burned stands with occasional selective logging, representing managed forests (secondary growth, unknown, we considered 3 – 4 ha of home range of thorn-tailed rayadito, based in results found for Aphrastura masafuerae (Hahn et al. 2010). Thus, sites were separated by a minimum linear distance of 1.6 km among them to ensure that adding and removing nest-boxes in one site would not affect birds in the other sites (Wiebe 2011). ...
... The role of nest-sites in limiting densities of cavity-nesting species has been widely studied (Newton 1998). Despite this, experiments with key resource management assessing nest-site limitation in old growth forests are rare and results appear less consistent (Cornelius et al. 2008, Wiebe 2011). In managed areas of TRSA, similar key resource addition experiments (Tomasevic and Estades 2006, Cornelius et al. 2008), conclude that nest-sites did limit population sizes of thorn-tailed rayaditos in breeding seasons in coastal and island locations. ...
... In the UK it is estimated that more than one in five gardens contains a bird nest box, equating to a minimum of 4.7 million nest boxes, nationally equivalent to the provision of one nest box for every six breeding pairs of cavity-nesting birds (Davies et al. 2009). The availability of suitable nesting sites limits breeding density (Newton 1998) and with the removal of mature and dead trees typical of suburbia, there will be fewer natural nest sites in such areas (Wiebe 2011). Buildings may provide some cavities, but modern or refurbished houses tend to have fewer potential nesting holes to compensate for this loss of nesting sites (Mason 2006;Shaw et al. 2008). ...
... Buildings may provide some cavities, but modern or refurbished houses tend to have fewer potential nesting holes to compensate for this loss of nesting sites (Mason 2006;Shaw et al. 2008). As a result, the provision of nest boxes in urban areas may be a particularly valuable resource, allowing cavity nesters to prosper (Chace and Walsh 2006;Wiebe 2011) and providing an opportunity to investigate factors affecting urban bird breeding biology. ...
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Nests are a critically important factor in determining the breeding success of many species of birds. Nevertheless, we have surprisingly little understanding of how local environment helps shape materials used in construction, how this differs among related species using similar nest sites, or if materials used directly or indirectly influence the numbers of offspring successfully reared. We also have little understanding of any potential links between nest construction and the assemblage of invertebrates which inhabit the nest and in particular, with ectoparasites. We addressed these questions by monitoring the success rates of nest-box using Blue Tits Cyanistes caeruleus and Great Tits Parus major, from rural, urban greenspace and urban garden settings. We collected used nests, identified arthropods present, and measured the proportions of highly processed anthropogenic materials used in their construction. Some 25% of Great Tit nest materials were of an anthropogenic source and this was consistent across habitats, while Blue Tits used little (1-2%) except in gardens (~16%), suggesting that Great Tits preferentially sought out these materials. In fledged nests, increasing use of anthropogenic material was associated with lower general arthropod diversity and ectoparasite predator abundance (Blue Tits only) but higher levels of Siphonapterans (fleas). Higher arthropod diversity was associated with lower flea numbers, suggesting that increased diversity played a role in limiting flea numbers. No direct link was found between breeding success and either anthropogenic material usage, or arthropod diversity and abundance. However, breeding success declined with increasing urbanisation in both species and increased with nest weight in Blue Tits. The interplay between urbanisation and bird ecology is complex; our work shows that subtle anthropogenic influences may have indirect and unexpected consequences for urban birds.
... These cavities are generally formed naturally or excavated by primary cavity-nesting birds, and are usually in limited supply so that they often limit the breeding opportunities of secondary cavity-nesting birds (Mitrus, Walankiewicz, & Czeszczewik, 2007, Cockle, Martin, & Drever, 2010, Warakai, Okena, Igag, Opiang, & Mack, 2013. Furthermore, in forests with human intervention and management, dead trees often fall down naturally or are removed to keep them away from fire, which further reduces nest cavity resources (Martin, Aitken, & Wiebe, 2004, Politi, Hunter, & Rivera, 2010, Wiebe, 2011, Kiss, Tokody, Ludnai, & Moskát, 2017. ...
... Some measures are effective to prevent these competitors, such as hanging the box far from forest edges to avoid occupation by Common Starlings Sturnus vulgaris (Stojanovic, Owens, Young, Alves, & Heinsohn, 2020) or providing small entrance holes to prevent being utilized by Common Mynas Acridotheres tristis and Rose-ringed Parakeets Psittacula krameri (Charter, Izhakib, Mochaa, & Kark, 2016). Normally, cavities are short resources in forests with human intervention and management (Wiebe, 2011). It is not proper to add nest boxes only tzarget a single bird species, because of the negative impact on the equilibrium of population. ...
Article
Artificial nest boxes may increase the abundance of nest sites for secondary cavity-nesting birds and provide more breeding opportunities. Since birds have strong preferences for certain characteristics of nest boxes, careful selection of installation sites can improve the occupancy rate of nest boxes and enhance reproduction. From 2016 to 2019, we studied the parameters affecting birds’ occupation of nest boxes in Xianrendong National Nature Reserve in Liaoning, northeast China. Among 241 nest boxes, five were occupied continuously for 4 years (1.6 %), 42 for 3 years (17.4 %), 69 for 2 years (28.6 %) and 88 for 1 year (36.5 %), with 37 (15.3 %) never being occupied for 4 years. The birds using the nest boxes were mainly cinereous tits (Parus cinereus), varied tits (Sittiparus varius), marsh tits (Poecile palustris), and Eurasian nuthatches (Sitta europaea). Our results showed that the occupation rates were positively correlated with nest box height, nest openness and proportion of conifers. Tree or pole that nestboxes are attached to also had a significant effect on occupation rates, and nest boxes hanging on conifer trees were occupied more often than those on deciduous trees and wooden telegraph poles. Breeding performance was not affected by occupation rates. These findings demonstrate that nest boxes should be hung high on a coniferous tree located in woodland with a higher ratio of conifers and open space in front of the nest when hanging nest boxes to attract small cavity-nesting birds.
... Thus, loss of nest sites in human-modified habitats can negatively affect abundance and diversity of birds [4,5]. Agricultural intensification in particular removes mature trees that are important sources of nesting cavities [6], and reductions in cavity-bearing trees can limit cavity-nesting bird populations and assemblages [7,8]. However, many cavity-dependent birds species will use artificial cavities, such as nest boxes, in areas where natural cavities are scarce. ...
... where transect j represented the random effect of transect j, and α 1,2,4,5,7,8 represented the logitlinear coefficients for model covariates [33]. Potential factors affecting kestrel detectability. ...
Article
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Nest boxes for predators in agricultural regions are an easily implemented tool to improve local habitat quality with potential benefits for both conservation and agriculture. The potential for nest boxes to increase raptor populations in agricultural regions is of particular interest given their positions as top predators. This study examined the effects of cherry orchard nest boxes on the local breeding population of a declining species, the American Kestrel (Falco sparverius), in a fruit-growing region of Michigan. During the 2013–2016 study, we added a total of 23 new nest boxes in addition to 24 intact boxes installed previously; kestrels used up to 100% of our new boxes each season. We conducted temporally-replicated surveys along four roadside transects divided into 1.6 km × 500 m sites. We developed a multi-season occupancy model under a Bayesian framework and found that nest boxes had strong positive effects on first-year site occupancy, site colonization, and site persistence probabilities. The estimated number of occupied sites increased between 2013 and 2016, which correlated with the increase in number of sites with boxes. Kestrel detections decreased with survey date but were not affected by time of day or activity at the boxes themselves. These results indicate that nest boxes determined the presence of kestrels at our study sites and support the conclusion that the local kestrel population is likely limited by nest site availability. Furthermore, our results are highly relevant to the farmers on whose properties the boxes were installed, for we can conclude that installing a nest box in an orchard resulted in a high probability of kestrels occupying that orchard or the areas adjacent to it.
... Tree cavities may result from decay processes, branch breakage, or from active excavation by woodpeckers and similar species (Remm and Lõhmus 2011). Under some conditions, such as in heavily managed or young forests, a paucity of cavities can limit populations of hole-nesting species (Newton 1994) but there is little experimental evidence of cavity limitation in old, unmanaged forests (Wiebe 2011). ...
... That abundance is likely due at least in part to this region having recently experienced the killing front of the beech bark disease complex, leaving most American Beech trees dead or dying and prone to cavity creation by decay or woodpeckers. Our finding of almost no use of nest boxes in mature forests suggest that any program intending to study or manage cavity-nesting species first conduct an assessment of cavity abundance in the targeted forest system before investing time and resources into nest boxes, as has been suggested by previous authors (Waters et al. 1990, Wiebe 2011. ...
Article
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Nest boxes are commonly used for species that utilize tree cavities, including small owls. Boxes were installed in 2011 to facilitate study of Northern Saw-whet Owls in Pennsylvania. We checked the 11 boxes that remained in 2020 after a hiatus of 8 years and found 3 rodent nests, but no evidence of owl usage. Playbacks revealed owls were present at 8 of 11 boxes checked. Cavity surveys yielded an average of 7.7 large cavities within 50 m of each box; extrapolation of cavity densities to a minimal territory size of 150 ha suggested that suitable cavities are an abundant, non-limiting resource here. Cavity abundance was likely a consequence of beech bark disease complex having recently top-killed most large American Beech trees locally, providing abundant resources for excavating woodpeckers. Assessing cavity abundance should be an essential first step for any management project involving cavity-nesting birds, and nest boxes should be used only in situations where cavities appear to be limited.
... In North America, excavators (especially woodpeckers) create most of the cavities that are subsequently reused by a diverse assemblage of secondary cavity nesters which cannot excavate their own holes Cockle et al., 2011). Depending on rates of cavity formation, the presence of landscape disturbances and the population densities of secondary cavity users, there may be high demand and competition for these breeding locations (Newton, 1994;Wiebe, 2011). Consequently, the same hole may be used repeatedly by multiple species (Raphael and White, 1984;Aitken et al., 2002;Blanc and Walters, 2008;Pakkala et al., 2017). ...
... Tree cavities are valuable and contested resources (Newton, 1994;Wiebe, 2011); the rate at which they are reused may depend on structural features of the cavity itself such as decay state or age (Bai et al., 2005;Koch et al., 2008;Cockle et al., 2019) and the location of the cavity tree in relation to landscape features such as forest edges or habitat types Remm et al., 2006). Here, we document for the first time that patterns of sequential occupancy were also associated with the species of secondary cavity users themselves. ...
Article
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Many animals require tree cavities for breeding and these sites may be reused by a diversity of secondary cavity nesters over a timespan of decades. It is unknown whether the reuse of holes changes their desirability as nest sites. We hypothesized that some species, “cavity destroyers,” degrade the quality of holes by filling them with coarse nest material or waste whereas excavating species, “cavity cleaners,” might prolong the use of a hole by removing debris or enlarging the hole. Using data gathered during 22 years from a field study in central British Colombia, we analyzed long-term patterns of cavity occupancy in relation to their sequential use by bird and mammal species, grouped by traits. Patterns of cavity occupancy were variable with 49% of 875 large-sized holes (excavated by northern flickers Colaptes auratus and pileated woodpeckers Dryocopus pileatus) and 19% of 652 smaller-sized holes incorporating runs of sequential use that lasted to 18 years. About 11% of large and 25% of small cavities also had gaps of 3–13 years between occupancies. Mammals, raptors and European starlings, consistent with the hypothesis, were cavity destroyers, occupying cavities as terminal users and before gaps more often than expected by chance. The pattern of occupancy by northern flickers was random in relation to gaps or prior use by other species. Although flickers did not target old holes to clean, neither did they avoid them. Small cavities that were renovated by flickers into larger cavities were reused at twice the rate after renovation. Runs of cavity occupancy that involved only cavity-destroying species were shorter than runs that involved periodic use by flickers, suggesting the woodpecker, through its cleaning and renovation, prolonged the use of such holes. Our study contributes insights on additional ecological factors, namely previous users, that can influence the use and availability of cavities over time.
... Nest-site limitation for SCNs is likely to occur in habitats where cavity density is low, but may disappear at higher cavity densities, where other factors such as food supply may be more limiting (Newton, 1994;Smith & Lindenmayer, 1988). The presence of many unoccupied cavities has led some to question the generality of nestsite limitation, especially in old forest ecosystems (Wesołowski, 2007;Wiebe, 2011); however, some cavities may be unsuitable or of low quality because of their size, location, age or history of use (e.g. Edworthy et al., 2018;Pakkala et al., 2019;Poonswad, 1995;Wiebe et al., 2020). ...
... Territoriality (Holt & Martin, 1997;Newton, 1998) and interspecific competition (Drake & Martin, 2020;Koch et al., 2012) can also restrict access to cavities, even when they appear to be available. Experiments with nest box additions and cavity removal support the hypothesis of nest-site limitation for some, but not all, secondary cavity-nesting birds across forest stands of various ages Cockle et al., 2010;Wiebe, 2011). ...
Article
Woodpeckers and other excavators create most of the holes used by secondary tree‐cavity nesting vertebrates (SCNs) in North American temperate mixedwood forests, but the degree to which excavators release SCNs from nest‐site limitation is debated. Our goal was to quantify how excavators maintain the diversity and abundance of secondary cavity nesters in a temperate forest through the creation of tree cavities. We examined the short‐ and long‐term (legacy) effects of excavators (principally woodpeckers, but also red‐breasted nuthatches and black‐capped chickadees) on forest biodiversity using longitudinal monitoring data (1732 nest cavities, 25 sites, 16 years) in British Columbia, Canada. Sites with higher densities of excavator nests had more cavities available, higher species richness of SCNs, and higher nest density of SCNs, indicating the importance of a standing stock of cavities. Years with higher nesting densities of excavators were followed by years with higher SCN diversity, indicating that the creation of nesting opportunities through fresh excavation releases SCNs from community‐wide nest‐site limitation. We also show that excavators leave a “legacy” of biodiversity (species richness and abundance) at a site by accumulating cavities at rates faster than they become unusable by decay or destruction. By quantifying site‐level effects of cavity excavation on the SCN community, our study highlights the key role of excavators as ecosystem engineers that maintain forest wildlife biodiversity.
... Studies on cavity-nesting birds have often supported the hypothesis of nest site limitations (Wiebe et al., 2006;Wiebe, 2011). However, the conclusions of these studies are weakened by the fact that they are multivariate and do not involve the treatment of each factor independently, masking their true importance as limiting resources in the habitat (Brush, 1983). ...
Article
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Cinclodes pabsti is an endemic passerine restricted to the highland areas in southern Brazil. The aim of this study was to provide information on its breeding biology. The nesting cavities along road cuts were monitored frombreeding season), and on a 2 to 4-days basis from August 2010 to January 2011. The geographic location, physical characteristics, and soil/substrate type in which the nesting cavities were situated were recorded. The total number of cavities used in the three breeding seasons was 136, resulting in 295 nests. The distance of a nest to its nearest neighbor ranged from 24-2,368 m, with a higher number of nests (n = 34; 59.7%) in the distance interval of 24-500 m. There was a greater usage of cavities located in Inceptisols, and the distances of nesting cavity entrances to the ground and to the top of road cuts were 1.6 ± 0.9 m and 0.8 ± 0.62 m, respectively. The breeding season lasted 148 days from mid-August to early January. Clutch size (n = 256) varied from 2 to 3 eggs, and the eggs (n = 155) had a total length of 27.2 ± 1.3 mm, breadth of 20.9 ± 0.8 mm, and mass of 6.2 ± 0.7 g. The incubation phase lasted 17.3 ± 0.8 days and the nestling phase for 18.3 ± 1.5 days. The body mass of the chicks was 6.0 ± 1.0 g just after hatching and reached a maximum of 59.6 ± 2.4 g at 16 days of age. Our results can contribute to filling the gaps in knowledge of C. pabsti ecology, because its habitat is under high anthropic pressures and the information on its life history is yet limited.
... Despite well-known successes of some management efforts, breeding site limitation cannot always be assumed (Gauthier and Smith 1987, Waters et al. 1990, Wiebe 2011) and, there are cases in which the provision of artificial breeding sites can have negative effects. ...
Article
Despite common use, the efficacy of artificial breeding sites (e.g., nest boxes, bat houses, artificial burrows) as tools for monitoring and managing animals depends on the demography of target populations and availability of natural sites. Yet, the conditions enabling artificial breeding sites to be useful or informative have yet to be articulated. We use a stochastic simulation model to determine situations where artificial breeding sites are either useful or disadvantageous for monitoring and managing animals. Artificial breeding sites are a convenient tool for monitoring animals and therefore occupancy of artificial breeding sites is often used as an index of population levels. However, systematic changes in availability of sites that are not monitored might induce trends in occupancy of monitored sites-a situation rarely considered by monitoring programs. We therefore examine how systematic changes in unmonitored sites could bias inference from trends in the occupancy of monitored sites. Our model also allows us to examine effects on population levels if artificial breeding sites either increase or decrease population vital rates (survival and fecundity). We demonstrate that trends in occupancy of monitored sites are misleading if the number of unmonitored sites changes over time. Further, breeding site fidelity can cause an initial lag in occupancy of newly installed sites that could be misinterpreted as an increasing population, even when the population has been continuously declining. Importantly, provisioning of artificial breeding sites only benefits populations if breeding sites are limiting or if artificial sites increase vital rates. There are many situations where installation of artificial breeding sites, and their use in monitoring, can have unintended consequences. Managers should therefore not assume that provision of artificial breeding sites will necessarily benefit populations. Further, trends in occupancy of artificial breeding sites should be interpreted in light of potential changes in the availability of unmonitored sites and the potential of lags in occupancy owing to site fidelity. This article is protected by copyright. All rights reserved.
... In managed forests, studies of breeding success in holenesting birds strongly suggest that nesting sites are a limiting resource (Dhondt, 2012;Miller, 2010;Remm & Lõhmus, 2011;S anchez et al., 2007;Wiebe, 2011). B. hypnorum, and a number of small mammals, overlap with birds in their use of this resource, and so nest sites may also be limiting for the Tree Bumble Bee, and this may result in competition. ...
Article
The Tree Bumble Bee, Bombus hypnorum, is a native of forest environments but has now successfully colonised urban areas. To better understand its success in an anthropogenic context, this review considers aspects of its natural history and nesting habits using a combination of published literature, anecdotal field observations by entomolo-gists from a number of countries, and information from the BWARS database. Where man's influence is minimal, B. hypnorum appears to nest almost exclusively in tree cavities. Modern woodlands tend to be managed and nest-cavity poor. Urban areas with gardens provide foraging opportunities together with a large supply of well-insulated and well-protected aboveground nest sites. B. hypnorum currently appears to do better in urban areas than managed woodlands, and quite possibly better than it ever did in primeval forest. In Britain, where it was first found in 2001, its notable success appears to reflect the absolute quantity of suitable anthropogenic, and specifically urban, nesting habitat. Conspicuous nest placement has resulted in more nest records for this recent arrival than exist for any native British bumble bee species. In "helping itself" to an anthropogenic nesting niche, B. hypnorum highlights how important appropriate nesting sites are in determining which bumble bee species can live in any given area. Detailed information on nest site preferences and availability needs to inform conservation measures for threatened native species.
... For urban design to attract certain birds that could breed in fragmented landscapes, one must also note the type of forest fragment retained -is it late or early successional forest? For instance, the Whitebreasted Nuthatch nests almost exclusively in cavities of large, mature trees (Wiebe, 2011). A late-successional forest fragment provides considerably more nesting opportunities than an early-successional forest with much smaller trees. ...
... Moreover, nest type may not only respond to environmental pressures in the habitat, but the type of nest a bird builds can also impact their fitness, distribution and dispersal capacities. For instance, species that nest in cavities are highly limited by nesting sites, and the distribution of these sites can constrain their dispersal 20,21 . If building domed nests offers protection from radiation, temperature, or predation, then it is possible that species with domed nests may be able to succeed in a wider variety of environments and may be able to disperse across larger ranges. ...
Article
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Avian nests present great variation in structure but, after excluding cavity nesters, probably the most obvious difference is that between open and domed nests. Some species lay their eggs in open structures, exposed to environmental variables, while other species build domed, enclosed nests with a roof, which are suggested to protect eggs and nestlings from weather conditions, high radiation levels, and predation. To date it is unclear which variables drove the evolution of different nest types. In this study, environmental and nest type information was extracted for continental Australian passerines, showing that species with open and closed nests are distributed in similar climates. However, species with open nests have larger ranges and are distributed in a wider variety of climatic conditions, suggesting open nests could be an evolutionary key innovation. This analysis was complemented with a detailed study of the evolution of particular nest traits in the largest Australasian avian radiation (Meliphagoidea), confirming that adult body size – but not environment – is an important factor in nest architecture, and larger species tend to build nests that are shallow and supported from underneath. Nest structure is a multidimensional trait that has probably evolved to match the phenotype of the nest owner, but that could also constrain or facilitate establishment in different environments.
... Th e number of cavities on the landscape is often thought to limit breeding populations of SCNs, something which may be true in anthropogenically-altered landscapes (Newton 1994) but seems unlikely in old growth forests (Wiebe 2011). Excavators can create a new hole themselves but their motivation to do so may be aff ected by the number and quality of existing holes. ...
Article
Woodpeckers are considered ecosystem engineers because they excavate tree cavities which are used subsequently by many species of secondary cavity nesters for breeding. Woodpeckers have the choice of excavating a new hole or reusing an existing one, and this propensity to excavate (e) may affect community dynamics but has rarely been investigated. Using 18 years of data on a population of northern flickers Colaptes auratus, I tested six hypotheses to explain the propensity to excavate (e) in a landscape which experienced two types of disturbance: pine beetles and wildfires. Woodpecker age, breeding experience and mate retention had little influence on e which varied between 13-39% annually and averaged 23% for 1843 first nests over the 18 years. Body size and body condition of males and females were not associated with e but rates of excavation declined seasonally, suggesting time rather than energy costs limited excavation effort. Reduced cavity availability mediated through high conspecific density coupled with wildfires triggered relatively high excavation rates, up to 39% but e decreased to baseline levels three years after the landscape disturbances. Nearly 2/3 of males did not excavate in their lifetime but apparently, e is great enough to balance the average rate of cavity tree loss in this forest which is 11% annually. Excavation propensity in flickers is flexible, but the birds reduce their work levels if there is a surplus of holes available. This article is protected by copyright. All rights reserved.
... Nest boxes have compensated the following: breeding site losses due to the removal of dead or decaying trees in managed forests (Remm et al. 2006;Sánchez et al. 2007), scarcity of hollows due to lack of trees of large diameter (Camprodon et al. 2008), and natural damage to holes (Newton 1994;Camprodon et al. 2008;Mazgajski 2009;Cockle et al. 2011). The introduction of nest boxes often leads to increases in the numbers of non-excavating hole-nesters (review in Newton 1998;Wiebe 2011). There are several examples of nest boxes being used as a conservation measure for secondary hole-nesters in agricultural areas and villages in cases where the availability of holes was the limiting factor: in Europe, the conservation programs of the Roller (Coracias garrullus) (Kovacs et al. 2008;Rodríguez et al. 2011;Kiss et al. 2017;Monti et al. 2019), Little Owl (Athene noctua) (Gottschalk et al. 2011) and Barn Owls (Tyto alba) (Johnson 1994); in Japan of the Dollarbird (Eurystomus orientalis) (Mine et al. 2014); and in the United States of the American Kestrel (Falco sparverius) (Katzner et al. 2005). ...
Article
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Modernization of urban buildings can decrease the availability of nesting sites in buildings, leading to sudden decreases in the density of avifauna. In this study, we investigated the use of nest boxes as a bird conservation measure after buildings were thermally modernized. In a 10 ha experimental area we mounted five types of nest boxes of different sizes and dimensions (a total of 132). Nest boxes were dedicated to species that lost access to their previous nesting sites. All species associated with the buildings significantly declined or disappeared. In the first year after the modernization, the House Sparrow ( Passer domesticus ) decreased by 66% compared with the period before the modernization, Eurasian Jackdaw ( Corvus monedula ) by 68%, Common Starling ( Sturnus vulgaris ) by 70%, and Common Swift ( Apus apus ) by 100%. In the first two years after the modernization, the birds nested only in nest boxes. Five years of monitoring showed that using nest boxes as compensation for bird nesting sites lost during the renovation of buildings can cause a population to recover to ca. 50% of its original level. To optimize deployments of nest boxes, wildlife managers should consider target species’ preferences for the dimensions and placement of boxes and limit the time boxes are used if a species prefers nesting outside nest-boxes, but in buildings (e. g. the House Sparrow) and does not require additional support.
... However, nest boxes can become ecological traps when a cue such as nest size leads cavity-nesters to prefer boxes over tree cavities despite boxes being located in areas of higher predation risk and/or lower food availability (and subsequently lead to lower reproductive success and/or survival [4]). Thus, local increases in breeding densities after the addition of nest boxes and other artificial cavities, as shown in many species [5][6][7][8][9], might be an insufficient metric in the assessment of this technique in promoting population recovery [10]. ...
Article
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Secondary cavity-nesting birds depend on tree cavities for nesting and roosting, but many studies of these birds are conducted using nest boxes. Implementation of effective conservation strategies for cavity-nesting species such as nest-site supplementation requires careful comparisons of fecundity and other vital rates for birds using both natural and artificial nest site types. We compared breeding phenology, clutch and brood sizes, and fledging success of Tree Swallows (Tachycineta bicolor) nesting in tree cavities and nest boxes during 2001–2003 in British Columbia, Canada. Swallows using nest boxes initiated egg-laying and hatched young at approximately the same time as those in tree cavities (2 June, 23 June, respectively). Female Tree Swallows in boxes laid larger clutches (5.9 ± 0.9 eggs, N = 76) than those in tree cavities (4.2 ± 1.6 eggs, N = 67). The mean number of nestlings hatched was greater in nest boxes (5.2 ± 1.1 nestlings, N = 67) than in tree cavities (2.6 ± 2.0 nestlings, N = 58). Pairs in boxes were over twice as successful in producing fledglings (93.4%; 57 of 61 pairs fledged > 1 young) than those in tree cavities (35.8%; 19 of 53 pairs). Of those successful nests, pairs nesting in boxes fledged 5.1 ± 1.1 young (N = 57), whereas those in tree cavities fledged 3.5 ± 1.2 young (N = 18). Because cavities in nest boxes averaged 60% larger in volume and 1.8 cm wider internally than tree cavities, we suggest that increased reproductive output was correlated with boxes enabling a larger clutch size. In previous research, we found that Tree Swallows were a poor competitor with other cavity-nesting passerines for tree cavities. The addition of nest boxes may serve as an effective way to supplement local reproduction for secondary cavity-nesting bird populations by reducing competition for limited nest sites. This is especially true in regions where the availability of natural nesting sites is highly variable, and where species compete with many other cavity-nesting passerines using a similar ecological niche and nesting cavities.
... Birds may have less energy expenditure during nest-site defence in high-quality territories, and this enhances the chance for survival of the species (Huhta et al., 1998;Kašová et al., 2014;Robles et al., 2011). On the other hand, in habitats with high tree and cavity densities, one would also expect higher breeding density of other cavity-nesters, increasing the nestsite competition frequency (e.g., Male et al., 2006;Newton, 1994;Vrublevska et al., 2015;Wiebe, 2011), although the intensity of nest defence may still not be driven by nest-site limitation (e.g., Wiebe, 2004). Because individual roles and the simultaneous behavioural repertoire of pairs altered in response to territory quality and potential nest-site competitor or brood predator, our results suggest that the cooperative nest-defence behaviour could be linked to the breeding success of this resident species living in heterogeneous forest habitats (e.g., Burtka & Grindstaff, 2015;Spoon et al., 2006). ...
... Although the low density of suitable hollows for birds to nest (see above) would point toward a possible lack of nest-sites which would limit the populations of hollow dependent birds in Iberian holm oak dehesas, I still reported low rate of tree-hollow occupation in dehesas. Hence experimental studies assessing avian breeding density responses to nest-supplementation and appropriate replication (see review in Wiebe, 2011) are necessary to firmly confirm nest site limitations in dehesas. ...
Article
Holm oak Quercus ilex dehesas cover large areas in the Mediterranean region, and constitute a paradigm of well preserved low-intensity agro-ecosystem supporting a high number of bird species. The canopy of holm oak trees is periodically pruned, but the role of pruning in the process of tree-hollow formation remains unstudied. Here I investigate the occurrence of tree-hollows in relation to tree characteristics (vitality, trunk diameter and fork height), infection by drilling Coleoptera and pruning intensity, and assess likely origin, use and suitability of hollows for non-excavator birds in dehesas of Spain. 26.3% of all sampled oaks had at least one hollow, and the number of pruning cuts predicted the occurrence of hollows. 97.0% of hollows were situated on pruning cuts suggesting that pruning may have favored decay cavity formation in Iberian dehesas. 43.6% of hollows were estimated suitable to hold the nest of a small-sized cavity-nesting bird, but only 11.9% might have potentially held the nest of a medium-sized cavity-nesting bird, rendering estimated 3.9 and 1.1 potential cavities/ha, respectively. The low densities of suitable hollows would point toward a lack of nest-sites which might limit cavity-nesting birds in holm oak dehesas. Future conservation actions targeting in protection of old and dead holm oak trees instead of selective removal, together with land-scale measurements of enhancement of riverine forests stands may enrich and ensure the persistence of cavity-using species in Iberian dehesas.
... However, even when the number of available cavities is high, the proportion of high quality cavities may limit occupancy (Cockle et al. 2008). Although cavities can indeed be an important limiting factor for forest dwelling birds (Cockle et al. 2008, Aitken andMartin 2012), sometimes there is also no clear relationship between the number of cavities and the density of breeding birds (Bonar 2000, Wiebe 2011). ...
Article
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Few studies have examined the patterns of co-occurrence between diurnal birds such as woodpeckers and nocturnal birds such as owls, which they may facilitate. Flammulated Owls (Psiloscops flammeolus) and Northern Saw-whet Owls (Aegolius acadicus) are nocturnal, secondary cavity-nesting birds that inhabit forests. For nesting and roosting, both species require natural cavities or, more commonly, those that woodpeckers create. Using day and nighttime broadcast surveys (n = 150 locations) in the Rocky Mountain biogeographic region of Idaho, USA, we surveyed for owls and woodpeckers to assess patterns of co-occurrence and evaluated the hypothesis that forest owls and woodpeckers co-occurred more frequently than expected by chance because of the facilitative nature of their biological interaction. We also examined co-occurrence patterns between owl species to understand their possible competitive interactions. Finally, to assess whether co-occurrence patterns arose because of species interactions or selection of similar habitat types, we used canonical correspondence analysis (CCA) to examine habitat associations within this cavity-nesting bird community. We found that Flammulated Owls co-occurred more with Hairy Woodpeckers (Picoides villosus), Northern Saw-whet Owls co-occurred with Northern Flickers (Colaptes auratus) and Red-naped Sapsuckers (Sphyrapicus nuchalis) and, when primary excavators were considered as a group, each species of owl was positively associated with the presence of woodpeckers. The owl species were distributed independently of one another suggesting a lack of competitive interactions. The CCA had relatively low explanatory power but suggested that habitat associations alone did not explain the patterns of positive co-occurrence we observed: Flammulated Owls and Hairy Woodpeckers associated with different habitats and Northern Saw-whet Owls, Northern Flickers, and Red-naped Sapsuckers appeared as habitat generalists. We interpret these patterns of co-occurrence and habitat use as evidence that woodpeckers facilitate presence of these species of owl and suggest management for forest owls could also include focus on the diurnal species with which they appear to associate.
... Tree cavities are an important reusable nesting resource for communities of cavity-nesting birds and mammals globally (Cockle et al. 2011, van der Hoek et al. 2017. Cavities support up to 30% of forest vertebrate biodiversity in some forest systems (Bunnell et al. 1999) but are often a limiting resource, especially in landscapes affected by forestry, agriculture, and urbanization (Newton 1994, Marzluff et al. 1998, Cockle et al. 2010, Wiebe 2011. To sustain populations of cavity-nesting vertebrates in the context of forest harvesting, managers can retain cavity-bearing trees or promote recruitment of new cavities. ...
Article
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Cavity-nesting birds and mammals exhibit species-specific nest-site selection for tree characteristics and cavity dimensions. Although trees and their cavities change as they age, with trees becoming softer and cavities becoming larger, it is not known how their value as nesting resources varies with age. In the context of wildlife and forest management, we investigated the relative value of generating a supply of fresh cavities, which are thought to be of high quality, versus protecting cavities as they age and expand in interior volume. For 21 years (1995–2016), we monitored the formation and occupancy of tree cavities used by >30 species of birds and mammals in interior British Columbia, Canada. Cavity occupancy by secondary users was highest 1 year post-excavation (53%), then declined to 40% after 2 years, remained at 33 ± 7% (SD) between 3 and 16 years of age, and increased to 50% use from 17–20 years post-excavation. Excavators that reused cavities (woodpeckers [Picidae], nuthatches [Sitta spp.]) strongly selected 1- and 2-year-old cavities, large-bodied non-excavators (ducks, raptors, squirrels) selected mid-aged cavities, and mountain bluebirds (Sialia currucoides) and tree swallows (Tachycineta bicolor) selected most strongly for the oldest cavities. Cavities created in living aspen trees (Populus spp.), especially those excavated by northern flickers (Colaptes auratus), maintained high occupancy by secondary users across cavity age, and provided the bulk of cavities used in this system. Altogether, these results show that a diverse excavator community is needed to generate a supply of fresh cavities in the ecosystem, and retention of the mid-aged and older cavities will help support larger species. © 2017 The Wildlife Society.
... Additionally, in these subtropical forests, logging has negatively affected the nest density of cavity-nesting birds 56 . This may also explain the decrease in the abundance of both excavators and secondary-cavity nesters, since logging reduces the availability of different and abundant trees, which may affect cavity-nesting 10,27,47,52 . ...
Article
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Logging causes changes in habitat structure, which can potentially lead to variations in taxonomic and functional richness of biodiversity. Studies on how functional traits in birds are afected by logging operations can provide an important element for the understanding of ecosystem processes. In this paper, we examined how logging in subtropical Andean forests infuenced taxonomic and functional diversity of cavity-nesting birds. We used these results to compare how logging afected ecosystem functions in temperate and subtropical forests of the Americas. We used point-counts to examine the efects of logging on taxonomic and functional traits in avian communities (Functional Richness, Functional evenness, Functional Divergence, and Community-weighted mean). We found that logging changed bird richness and abundance, although it had no efect on the functional response to the measured traits. The comparison of our results with those of temperate forests of Canada and Chile reveals diferences in the functional richness of birds in these habitats, with a lower impact of logging on functional traits. We highlight the importance of including functional traits in the analyses, since the reduction in the species richness and abundance may not be translated into functional changes within the ecosystem.
... Approximately 13% of tree-cavity-nesting species are recognized as vulnerable, endangered or critically endangered by the IUCN, similar to the percentage of all threatened bird species in the world (BirdLife International, 2016). Although many of the facultative cavity users in Table S1 (at least 69 species) use tree cavities only rarely, and are unlikely to depend on them for survival, availability of cavities can be an important limiting factor for many other tree-cavity-nesting species or populations (see e.g., Cockle et al., 2011;Cornelius et al., 2008;Pöysä & Pöysä, 2002;Wiebe, 2011). The elimination of trees with cavities through processes such as logging or forest clearing for agriculture or urbanization may lead to population declines that can endanger the persistence of intact tree-cavity-nesting communities (Politi et al., 2009;Politi, Hunter, & Rivera, 2010;Cockle et al., 2010;Wesołowski & Martin, in press). ...
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Aim: Globally, many bird species nest in tree cavities that are either excavated or formed through decay or damage processes. We assembled an overview of all tree-cavity nesters (excavators and non-excavators) in the world, analysed their geographic distribution and listed the conservation status of all species. Location: This is a global analysis of species from every continent except for Antarctica where the lack of trees precludes the occurrence of this group. Methods: We reviewed the online version of the Handbook of the Birds of the World Alive, http://www.hbw.com/, and primary literature for species known to nest in tree cavities, with tree cavities defined as holes that a bird can enter such that it is not visible from the outside. We classified species by nester type (excavator or non-excavator, and obligate or facultative where possible), conservation threat status and zoogeographic region, and tested for statistical differences in species distributions across realms using chi-square tests. Results: At least 1878 species (18.1% of all bird species in the world) nest in tree cavities, of which we considered 355 to be primary excavators, 126 facultative excavators and 1357 non-excavators (we were unable to classify nesting type for 40 species). At least 338 species use cavities created by woodpeckers (Picidae), excluding reuse by woodpeckers themselves. About 13% (249 species) of tree-cavity nesters experience major threats (i.e., status of vulnerable, endangered or critically endangered). The highest richness of tree-cavity nesters is found in the Neotropical (678 species) and Oriental (453) regions, and the highest proportion of threatened species in Australasia (17%). Main conclusion: Maintenance of a continual supply of cavities, a process in which woodpeckers and the processes of decay play critical roles, is a global conservation priority as tree cavities provide important nesting sites for many bird species.
... There are ∼100 species of cavity-breeding birds in the Palearctic and 128 in the Nearctic (Wesołowski and Martin Forthcoming). Cavity availability does not seem to limit most bird populations in old-growth unmanaged forest (Wiebe 2011), but in younger managed forest the populations of some nonexcavating bird species appear to be limited by the availability of high-quality cavities (Newton 1994). Moreover, cavity users are overrepresented among threatened taxa in managed forest (e.g. ...
Article
In forests worldwide, ∼10−40% of bird and mammal species require cavities for nesting or roosting. Although knowledge of tree cavity availability and dynamics has increased during past decades, there is a striking lack of studies from boreal Europe. We studied the density and characteristics of cavities and cavity-bearing trees in three categories of forest in a north-Swedish landscape: clearcuts with tree retention, managed old (>100 years) forest, and unmanaged old forest. Unmanaged old forests had significantly higher mean density of cavities (2.4±2.2(SD) ha⁻¹) than managed old forest (1.1±2.1 ha⁻¹). On clearcuts the mean cavity density was 0.4±2.3 ha⁻¹. Eurasian aspen (Populus tremula) had a higher probability of containing excavated cavities than other tree species. There was a greater variety of entrance hole shapes and a higher proportion of cavities with larger entrances in old forest than on clearcuts. Although studies of breeding success will be necessary to more accurately assess the impact of forest management on cavity-nesting birds, our results show reduced cavity densities in managed forest. To ensure future provision of cavities, managers should retain existing cavity-bearing trees as well as trees suitable for cavity formation, particularly aspen and dead trees.
... Introduction Tree hollows (also referred to as tree holes or cavities) provide vital refuges for a broad range of fauna worldwide [1][2][3][4]. As hollow-dependent animals often spend over half their lives within roosts, nests and dens [5], the availability and quality of these resources significantly influences energetics [6], social interactions [7], breeding success [8,9], survival [10], and population size [11]. Forestry practices, land clearing for agricultural intensification or urban expansion, and the removal of senescent trees in urban areas (due to public safety concerns), have resulted in a significant reduction in the number of mature hollow-bearing trees in human-impacted landscapes worldwide [12]. ...
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Thermal properties of tree hollows play a major role in survival and reproduction of hollow- dependent fauna. Artificial hollows (nest boxes) are increasingly being used to supplement the loss of natural hollows; however, the factors that drive nest box thermal profiles have received surprisingly little attention. We investigated how differences in surface reflectance influenced temperature profiles of nest boxes painted three different colors (dark-green, light-green, and white: total solar reflectance 5.9%, 64.4%, and 90.3% respectively) using boxes designed for three groups of mammals: insectivorous bats, marsupial gliders and brushtail possums. Across the three different box designs, dark-green (low reflectance) boxes experienced the highest average and maximum daytime temperatures, had the greatest magnitude of variation in daytime temperatures within the box, and were consis- tently substantially warmer than light-green boxes (medium reflectance), white boxes (high reflectance), and ambient air temperatures. Results from biophysical model simulations demonstrated that variation in diurnal temperature profiles generated by painting boxes either high or low reflectance colors could have significant ecophysiological consequences for animals occupying boxes, with animals in dark-green boxes at high risk of acute heat- stress and dehydration during extreme heat events. Conversely in cold weather, our model- ling indicated that there are higher cumulative energy costs for mammals, particularly smaller animals, occupying light-green boxes. Given their widespread use as a conservation tool, we suggest that before boxes are installed, consideration should be given to the effect of color on nest box temperature profiles, and the resultant thermal suitability of boxes for wildlife, particularly during extremes in weather. Managers of nest box programs should consider using several different colors and installing boxes across a range of both orienta- tions and shade profiles (i.e., levels of canopy cover), to ensure target animals have access to artificial hollows with a broad range of thermal profiles, and can therefore choose boxes with optimal thermal conditions across different seasons.
... This dependence is particularly known for cavity adopters among birds, which are known to reflect not only the number of available cavities (Newton, 1994;Gibbons and Lindenmayer, 2002;Heinsohn et al., 2003;Cockle et al., 2010) but also their quality (Cockle et al., 2008). The limited availability of cavities is characteristic particularly for human-altered habitats (Wiebe, 2011) whereas the cavities are not considered limiting nesting resources when being superabundant as are the cavities in mature forests (Wesołowski, 2007). Cavity adopters among birds leave many, up to 97%, of available cavities in natural forests unoccupied, but many (but not all) of their populations increase after the provisioning of additional high-quality cavities. ...
Article
Observational studies have suggested that the presence of snail shells correlates with the presence of specialized adopters, particularly bees and wasps (Hymenoptera: Aculeata). However, should the empty shells be considered limiting resources once they are present in the respective habitat even if observational studies suggested low ratio of occupied relative to total shells? We performed a manipulative experiment, which consisted of the addition of marked snail shells of six terrestrial species that dominate the open and semi-open central European habitats to 21 sites with naturally present shells. We deployed the shells for the spring and summer 2017, allowed their inhabitants to undergo a diapause during the follow-up winter period and complete metamorphosis. The specialized bee and wasp species abundantly occupied the provided shells and the occupancy rates were several times higher in experimentally provided shells compared to the naturally present shells. These differences in occupancy rates were higher at anthropogenic compared to natural sites and at sites with more limited availability of naturally present shells. In contrast, the few sites at which the examined resource was superabundant, both the naturally present and the experimentally provided shells were occupied only to a limited extent. The species composition of assemblages that occupied the experimentally provided and naturally present shells were similar, and the differences in species composition between the natural and anthropogenic sites resembled those exhibited in the naturally present shells. In conclusion, we experimentally confirmed that empty snail shells serve as limiting resources for specialized bees and wasps even at sites where the naturally present shells are perceived as abundant.
... Secondary cavity nesters, those bird species that rely on the presence of existing cavities generated by other species (woodpeckers) or natural processes (wood decay by fungi), are highly vulnerable to anthropogenic and stochastic processes that reduce the availability of cavity bearing trees (Newton, 1994;Cornelius et al., 2008;Politi et al., 2009;Cockle et al., 2010). Many studies conducted in mature or unmanaged forest suggest that breeding populations of cavity-nesting birds are not limited by availability of nest sites (Brightsmith, 2005;Wesołowski, 2007;Zheng et al., 2009;Wiebe, 2011;Rivera et al., 2012;Altamirano, 2014;Ibarra et al., 2020). However, other studies suggest that for some cavity nesting birds, even in cavity-rich forests, the most important limiting factor is availability of suitable cavities for nesting (cavities with specifics characteristics or quality) rather than overall cavity abundance (Cockle et al., 2010;Aitken and Martin, 2012;Robles et al., 2012;de la Parra-Martínez et al., 2015). ...
Article
Secondary cavity nesters, bird species that rely on the presence of existing cavities, are highly vulnerable to anthropogenic and stochastic processes that reduce the availability of cavity bearing trees. The most common logging practice in Neotropical forests is selective logging, where a few valuable tree species are logged, primarily old, large trees that are the most prone to develop cavities and produce larger amounts of fruits and seeds. Tucuman Amazon, Amazona tucumana, is a threatened parrot that relies on the tree-cavities and food provided by large, old trees. Our objective was to evaluate how logging affects 1) stand and nest plot forest structure, 2) nesting site selection, 3) food availability, 4) density of suitable cavities, 5) nest density, and 6) nest spatial pattern of Tucuman Amazon by comparing a mature undisturbed forest in a National Park (NP) vs a logged forest (LF). We determined the availability of suitable cavities and food resources consumed by Tucuman Amazon, and we compared nest density and spatial pattern of nests between NP vs LF. The Index of food availability for all tree species consumed by Tucuman Amazon and for P. parlatorei were significantly higher in NP than in LF (34.5 ± 13.3 m ha − 1 vs. 3.5 ± 1.0 m ha − 1 and 5.6 ± 2.3 m ha − 1 vs. 1.2 ± 1.0 m ha − 1 , respectively). Density of suitable cavities for nesting in the NP was significantly higher than in the LF: 4.6 cavities ha − 1 [C.I. 95 %: 3.07-7.04 cavities ha − 1 ] vs. 1.1 cavities ha − 1 [C.I. 95 %: 0.73-1.66 cavities ha − 1 ], respectively. Mean density of Tucuman Amazon nests was significantly higher in the NP than in LF (0.25 ± 0.04 vs. 0.06 ± 0.04 nest ha − 1 , respectively). Food availability is an important factor that affects Tucuman Amazon populations and when food is not limiting, the availability of suitable cavities and territorial behavior could play a role in regulating nest density. When evaluating the limiting factors for secondary cavity-nesting species of conservation concern it is important to evaluate the interplay of a set of potential limiting factors to propose sound forest management recommendations.
... Studies on cavity-nesting birds have often supported the hypothesis of nest site limitations (Wiebe et al., 2006;Wiebe, 2011). However, the conclusions of these studies are weakened by the fact that they are multivariate and do not involve the treatment of each factor independently, masking their true importance as limiting resources in the habitat (Brush, 1983). ...
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Cinclodes pabsti is an endemic passerine restricted to the highland areas in southern Brazil. The aim of this study was to provide information on its breeding biology. The nesting cavities along road cuts were monitored frombreeding season), and on a 2 to 4-days basis from August 2010 to January 2011. The geographic location, physical characteristics, and soil/substrate type in which the nesting cavities were situated were recorded. The total number of cavities used in the three breeding seasons was 136, resulting in 295 nests. The distance of a nest to its nearest neighbor ranged from 24-2,368 m, with a higher number of nests (n = 34; 59.7%) in the distance interval of 24-500 m. There was a greater usage of cavities located in Inceptisols, and the distances of nesting cavity entrances to the ground and to the top of road cuts were 1.6 ± 0.9 m and 0.8 ± 0.62 m, respectively. The breeding season lasted 148 days from mid-August to early January. Clutch size (n = 256) varied from 2 to 3 eggs, and the eggs (n = 155) had a total length of 27.2 ± 1.3 mm, breadth of 20.9 ± 0.8 mm, and mass of 6.2 ± 0.7 g. The incubation phase lasted 17.3 ± 0.8 days and the nestling phase for 18.3 ± 1.5 days. The body mass of the chicks was 6.0 ± 1.0 g just after hatching and reached a maximum of 59.6 ± 2.4 g at 16 days of age. Our results can contribute to filling the gaps in knowledge of C. pabsti ecology, because its habitat is under high anthropic pressures and the information on its life history is yet limited.
... Western Bluebirds are able to mate the year after they hatch. Secondary cavity-nesting species, such as the Western Bluebird, are limited by the number of available cavities in a given area and may therefore suffer from limited breeding opportunities (Wiebe 2011). Song et al. (2016) found that offspring sex ratios of a secondary cavity-nesting species were male-biased in areas with more nest-sites. ...
Article
Mothers may produce more of one sex to maximize their fitness if there are differences in the cost of producing each sex or there are differences in their relative reproductive value. Breeding date and clutch size are known to influence offspring sex ratios in birds through sex differences in dispersal, social behaviours, differential mortality, and available food resources. We tested if breeding date, clutch size and drought conditions influenced offspring sex ratios in a sexually size-monomorphic species, the Western Bluebird, by interrogating a 21-year dataset. After controlling for differential mortality, we found that hatch dates late in the breeding season were associated with the production of more females, suggesting that the value of producing males declines as the breeding season progresses. When clutch size was taken into account, small clutches yielded significantly more females late in the breeding season compared to the early and middle parts of the breeding season that produced significantly more males. Large clutches early in the season tended to produce more females, although this was not significant. Drought severity was not correlated with sex ratio adjustment. We propose and discuss several explanations for these patterns, including male offspring, but not female offspring, acting as helpers, increased female nestling provisioning late in the breeding season, differences in food abundance, and egg-laying order. Future work will help to uncover the mechanisms leading to these patterns. Identifying patterns and mechanisms of sex ratio skew from long-term datasets is important for informing predictions regarding life-history trade-offs in wildlife populations.
... Nest-site characteristics can also reduce predation pressure (Martin and Pingjun Li 1992;Chalfoun and Schmidt 2012) but suitable or safe sites are often a limited resource (Newton 1994;Aitken andMartin 2012, however, see Wesołowski 2007). For example, secondary cavity-nesters often prefer small entrance sizes and deep cavities that limit predator access (Wesołowski and Rowiński 2004;Koch et al. 2008;Lambrechts et al. 2010;Cockle et al. 2015), but at the cost of higher intra-and interspecific competition (Wiebe 2011;Aitken and Martin 2012). ...
Article
Breeding- and nest-site choice is a behavioral strategy often used to counter negative interactions. Site choices before breeding prevent costs of predation and competition but have been neglected in the context of brood parasitism. For hosts of brood parasites, the earlier brood parasitism is prevented in the breeding cycle the lower the future costs. Suitable nest-sites for cavity-nesting common redstarts (Phoenicurus phoenicurus), a host of the common cuckoo (Cuculus canorus), are a limited resource, but their cavity-nesting strategy could potentially deter predators and brood parasites. We altered the entrance size of breeding cavities and investigated redstart nest-site choice and its consequences to nest predation and brood parasitism risk, although accounting for potential interspecific competition for nest sites. We set-up paired nest-boxes and let redstarts choose between 7 cm and 5 cm entrance sizes. Additionally, we monitored occupancy rates in nest-boxes with 3 cm, 5 cm, and 7 cm entrance sizes and recorded brood parasitism and predation events. We found that redstarts preferred to breed in 5 cm entrance size cavities, where brood parasitism was eliminated but nest predation rates were comparable to 7 cm entrance size cavities. Only in 3 cm cavities both, brood parasitism and predation rates were reduced. In contrast to the other cavity-nesting species, redstart settlement was lowest in 3 cm entrance size cavities, potentially suggesting interspecific competition for small entrance size cavities. Nest-site choice based on entrance size could be a frontline defense strategy that redstarts use to reduce brood parasitism.
... A variety of other wildlife from raptors to squirrels to mustelids have overlapping cavity needs (Pfannmuller et al., 2017;P€ oyry, 1994). Cavity availability structures the interactions within and between these species (i.e., "nest-webs"; Martin & Eadie, 1999;Martin et al., 2004), and likely influences population dynamics, especially in managed landscapes (Newton, 1994;Wiebe, 2011). Thus, mapping the fine-scale occurrence of cavities suitable for nesting Wood Ducks across the landscape would benefit conservation practices for additional wildlife and provide a useful methodological case-study for other cavity-nesting communities. ...
Article
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Tree cavities are an essential habitat component for wildlife species across diverse taxa, from insects to large mammals. Many of these species are imperiled by loss of cavities. Further, conservation action is hindered by limited information on the spatial distribution of cavities, largely due to difficulties in developing useful models of their presence or abundance. Accurately predicting the fine‐scale, landscape‐wide, spatial distribution of these important habitat features would greatly benefit conservation measures. In this study, we evaluated the efficacy of using remotely sensed data, including LiDAR, multispectral imagery, and SAR, to predict the locations of cavities suitable for nesting Wood Ducks Aix sponsa at fine scales (≤40 × 40 m) and across a broad landscape (~254 000 ha). We used Random Forest models to classify the presence–absence of cavities at four spatial scales of prediction (5, 10, 20, and 40‐m pixels) as well as three groupings of predictor variables (LiDAR‐derived metrics, spatial forest‐inventory variables [derived via LiDAR or imagery], and ancillary remotely sensed data [derived via SAR or imagery]), and then compared the accuracy between models. The 20‐m response‐scale had the highest accuracy. Variables from each of the groupings were important and largely relied on multispectral imagery and LiDAR data. Our final model and predictive map had 84% overall Out of Bag accuracy and, when tested with an independent cavity dataset, correctly identified 80% of trees with suitable cavities as presences. The predictive map can be used by researchers and land‐managers to determine how past management actions have affected cavity availability as well as the locations of habitat complexes for Wood Ducks and, potentially, other secondary‐cavity‐nesting wildlife. In addition, our analysis can serve as a methodological case‐study for cavity‐nesting wildlife in other regions, as the use of remotely sensed data like high‐density LiDAR and multispectral imagery increases. Tree cavities are an essential habitat component for wildlife species across diverse taxa, from insects to large mammals. Accurately predicting the fine‐scale, landscape‐wide, spatial distribution of these important habitat features would greatly benefit conservation measures. Our principal finding was that remotely‐sensed data, including LiDAR and multispectral imagery, can be used to accurately predict and map the spatial occurrence of tree cavities across broad regions and at fine spatial resolutions.
... Extrapolating the results obtained from nest boxes to natural cavities must be done cautiously (Wesołowski 2011). The managed forests of our study site had few natural cavities but there may be little competition for cavities in some old, unmanaged forests (Czeszczewik and Walankiewicz 1999;Wiebe 2011). Therefore, the usurpation hypothesis should be studied in other forest types and in relation to the depths of natural cavities. ...
Article
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Some birds cover their eggs with nest material when they leave to forage. It has been suggested that such egg-covering aids thermoregulation or prevents predation but here we present a new hypothesis, that secondary cavity-nesting species cover their eggs to prevent nest usurpation by other birds. When the bottom of the cavity is dark, as when eggs are covered by nest material, it may be difficult for a prospecting competitor to see whether a defending nest owner or a predator is hiding inside the cavity. Competitors may therefore hesitate to enter dark cavities. We filmed 21 great tit ( Parus major ) nests during the egg-laying period and found that the female spent bouts of highly variable length outside the nest box (range 0.3–250 min, n = 51), so prospecting small passerines would have difficulty predicting whether an aggressive tit owner was in the box or would soon return. We presented prospecting male pied flycatchers ( Ficedula hypoleuca ) with a dyad of boxes ( n = 93), each containing a great tit nest but only one with visible eggs. Flycatchers hesitated more to enter a nest box with no visible tit eggs than a box with exposed eggs. This was most evident for nest boxes with dark versus light interior paint, supporting the idea that better interior illumination makes prospecting birds more confident about entering an unfamiliar cavity. The usurpation and predation hypotheses are not mutually exclusive because both competitors and small predators may hesitate to enter dark, enclosed spaces if visibility is low. Significance statement Some birds deposit a layer of material on top of the eggs when they leave the nest. Several hypotheses have been proposed for such egg covering, for example that it may insulate the eggs and reduce the risk of nest predation. We propose a new hypothesis, namely that secondary hole-nesting birds cover their eggs when they leave the nest to prevent usurpation of the cavity by other birds. Great tits that we filmed at the nest during the egg-laying period could be absent for long periods. To test the hypothesis, we presented male pied flycatchers, potential nest competitors, with a dyad of nest boxes, each containing a great tit nest but only one with visible tit eggs. In support of the prediction, prospecting flycatchers hesitated to enter dark cavities with dark floors relative to boxes with exposed, reflective eggs.
... The availability of cavities is crucial in determining the importance that competition for space may have in tropical ecosystems. This fact has been highlighted in studies conducted in mature temperate forest where competition among passerines for natural cavities is practically non-existent, in marked contrast to managed forest areas where the scarcity of tree cavities promotes strong competition (Cornelius et al. 2008, Wesolowski 2007, reviewed by Wiebe 2011). Similarly, the availability of nest cavities is strongly reduced in savanna in relation to forest in the tropical ecosystems considered in this study (pers. ...
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Convergence in the use of resources may occur between distantly related organisms. A major ecological resource in which members of various taxa may be interested is a cavity for nesting. A variety of social hymenopterans and vertebrates may nest within tree cavities in tropical ecosystems. We used 241 nest-boxes placed in seven Kenyan localities to investigate the use of nesting cavities by members of distant taxa and discuss whether interaction between them is a potential factor shaping cavity-nester communities in tropical regions. The nest-boxes were occupied by social insects (ants, bees and wasps) (30.1% of nest-boxes in April-May and 33.1% in September-October) and vertebrates (birds and mammals) (20% and 7.7%, respectively). Hymenopterans were more abundant in forest boxes (36.2% of nest-boxes occupied in April-May and 37% in September-October), whereas savannas had lower figures (21.7% and 31.3%, respectively). Among vertebrates, most occupants of nest-boxes in savanna were birds (17.8% of nest-boxes occupied vs. 8% in mammals), while mammals predominated in forests (4.9% of the nest-boxes occupied vs. 0.3% in birds). Spatial and temporal patterns of occupation highlight the potential that interaction between distant taxa may have on the access to nesting cavities. More nest-boxes remained unoccupied in forested areas than in savanna areas suggesting that a shorter supply of nesting sites in the savanna may be a source of competition. The simultaneous occupation of a nest-box by two different taxa was exceptional, also supporting the hypothesized inter-taxon competition.
... Use of artificial nest cavities. Although most studies are to some extent equivocal (Wiebe 2011), suitable cavities are generally thought to limit populations and reproduction of secondary cavity-nesting species (Newton 1994(Newton , 1998. A good example is the endangered Redcockaded Woodpecker (Dryobates borealis), for which artificial cavities have been used to successfully increase the number of breeding groups in recovering populations (Copeyon et al. 1991). ...
Article
Although primary cavity-nesting species are capable of excavating new cavities, they often reuse old ones. To determine potential factors driving such reuse, we studied nest-cavity reuse in the Acorn Woodpecker (Melanerpes formicivorus), a cooperatively breeding species that reuses old cavities for 57.2% of nests at Hastings Reservation in central coastal California, USA. We found no evidence for significant fitness costs or benefits of cavity reuse compared to using newly constructed cavities. In contrast, several lines of evidence supported a role for constraints on both cavity reuse and on new cavity construction. The main constraint on reuse was cavities failing to survive from one year to the next, usually because the limb fell apart, filled with water, or was usurped by another species. Evidence that constraints on new cavity construction may be important included more frequent cavity reuse when groups renested and use of artificial cavities when they were experimentally provided. Nest-cavity reuse in this population appears to be driven primarily by constraints, including the energetic costs and time required to excavate a new cavity, rather than fitness consequences, even though Acorn Woodpeckers regularly excavate small holes in trees for acorn storage and the energetic costs of new cavity construction are apparently insufficient to significantly depress reproductive success. Constraints play a significant role in cavity reuse and may affect both the intraspecific and interspecific frequency of cavity reuse among facultative excavating species.
... The plumage of A. collaria, which lives in the moist lowland, mountains, and mangrove forests, and often feeds on plantations and rural gardens, is also green, but with a pink throat and neck. Nest predation is the main factor limiting reproduction for most birds [126,127] and it is the major factor for the parrots in Jamaica, as the nesting success in either species is close to 50% [124,125], which is low compared to 60-70% for the other island Amazona parrots that nest in tree hollows [15]. A. collaria may require larger trees in which to successfully rear young, and the nest site availability may be a stronger limiting factor for them [128]. ...
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Amazon parrots (Amazona spp.) colonized the islands of the Greater Antilles from the Central American mainland, but there has not been a consensus as to how and when this happened. Today, most of the five remaining island species are listed as endangered, threatened, or vulnerable as a consequence of human activity. We sequenced and annotated full mitochondrial genomes of all the extant Amazon parrot species from the Greater Antillean (A. leucocephala (Cuba), A. agilis, A. collaria (both from Jamaica), A. ventralis (Hispaniola), and A. vittata (Puerto Rico)), A. albifrons from mainland Central America, and A. rhodocorytha from the Atlantic Forest in Brazil. The assembled and annotated mitogenome maps provide information on sequence organization, variation, population diversity, and evolutionary history for the Caribbean species including the critically endangered A. vittata. Despite the larger number of available samples from the Puerto Rican Parrot Recovery Program, the sequence diversity of the A. vittata population in Puerto Rico was the lowest among all parrot species analyzed. Our data support the stepping-stone dispersal and speciation hypothesis that has started approximately 3.47 MYA when the ancestral population arrived from mainland Central America and led to diversification across the Greater Antilles, ultimately reaching the island of Puerto Rico 0.67 MYA. The results are presented and discussed in light of the geological history of the Caribbean and in the context of recent parrot evolution, island biogeography, and conservation. This analysis contributes to understating evolutionary history and empowers subsequent assessments of sequence variation and helps design future conservation efforts in the Caribbean.
... Competition from heterospecifics may vary among habitats and across the geographical range but presumably the level of pied flycatcher intrusion in our study was low enough to make defence of extra sites worthwhile. Great tits are quite flexible in choice of nest site (Maziarz et al., 2015), and in unmanaged forests, to which they presumably are most adapted, there may be an excess of such sites at least in some habitats (Czeszczewik & Walankiewicz, 1999;Wiebe, 2011) and so tit aggression levels may sometimes be low. Our study was in managed forests with few natural holes. ...
Article
Interspecific competition is expected when two species share resource needs. For example, secondary cavity‐nesting birds may compete vigorously for suitable nest sites both within and among species. However, little is known of whether monogamous species defend more than one nest site on their territory after breeding has begun, and in particular whether they are aggressive against other species. Defending extra nest sites may be adaptive because they may be used for renesting after a failure or to produce a second brood. We studied interactions between a monogamous, resident bird, the great tit Parus major and a migrant, the pied flycatcher Ficedula hypoleuca, providing nest boxes in woodlands in Norway. Agonistic behaviours may be subtle and easily overlooked so we experimentally placed caged male pied flycatchers near nests of great tits and at a dyad of empty nest boxes erected in the territory 25 m away. We filmed interactions between species at 21 sites in the egg‐laying period of the tit, and at 26 nest sites during incubation. Male great tits showed aggression towards the caged flycatcher both at their own nest box and at the nest boxes erected at a distance. We manipulated the external appearance of the nest boxes with painted designs around the entrances but the intensity of aggression at the empty nest boxes did not depend on whether those boxes matched the nest box with the tit nest and was not correlated with tit clutch size. Neither was the intensity of display activity at each nest box by the flycatchers that settled associated with these variables. The results are discussed in relation to hypotheses for nest site choice involving interspecific social learning and aggression.
... Widespread deforestation since the middle of the twentieth century makes such trees extremely rare in area close to wetlands in Northeast China (Zheng et al. 2016). Just as the abundance of cavity-nesting bird species can be limited well below potential carrying capacity by lack of natural holes in young even aged tree stands (Wiebe 2011), Oriental Storks may suffer from a similar limitation by lack of suitable nest sites despite an abundance of suitable feeding habitats on the wetlands. The rapid uptake and successful use of artificial nest sites following their provision supported a major increase in breeding Oriental Stork abundance at Honghe National Nature Reserve (Li 1995;Zhu et al. 2008), a case that provides evidence that the number of breeding pairs was limited by availability of nest-sites, indicating that, at least at local scales, nest-sites may be limited. ...
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In this study, we report the first ever documented instances of attempted and successful reproduction (rearing two offspring) of Oriental Storks ( Ciconia boyciana ) at age 2 years in a wild population in the middle Heilongjiang-Amur River Basin in Russia, using a combination of GPS-GSM tracking, DNA sex identification and field verification.
... The ability to access and monitor sites in which free-ranging birds roost and reproduce has provided unique insights into avian natural history and ecology (Newton 1994, Visser et al. 2003, Both et al. 2004, Blondel et al. 2006, Griffith et al. 2008, Steenhof and Peterson 2009. Nest box monitoring programs can also serve as a conservation tool for declining species and/ or species that are experiencing a decline in natural nest cavities (Hamerstrom et al. 1973, Spring et al. 2001, Wiebe 2011, Libois et al. 2012 with careful consideration of the benefits and limits of such programs . ...
... nester ecology and conservation (Newton 1994(Newton , 1998Martin & Eadie 1999;Wesołowski 2007). However, a suite of studies suggests that there is no nest-site limitation in old-growth forests (Wiebe 2011). For example, a cavity density of 60 ha À1 was found but only 5-9% of them were used in forests of Central Sweden (Carlson et al. 1998). ...
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Tree cavities are a keystone resource for many wildlife species worldwide. In Andean temperate forests of South America, many species of birds, mammals and reptiles use cavities to achieve their life history requirements. However, information on cavity supply and drivers of cavity production in these forests remains largely undocumented. We examined the patterns of tree-cavity supply in successional native forests, exploring the potential drivers of cavity occurrence and relative abundances in Andean temperate ecosystems of southern Chile. In 10 forest stands, we established 369 vegetation plots and measured 7951 trees. For each tree, we recorded the species and measured the diameter at breast height (DBH), decay class and number of cavities. While tree density was much higher in secondary than in old-growth forest stands, the density of nonexcavated cavities was higher in old-growth than in secondary forests. Cavity occurrence and relative abundances (number of cavities per tree) were higher in large decaying and standing dead trees (i.e. habitat legacies) than in young healthy trees. Importantly, DBH and decay had a stronger influence on the supply of nonexcavated than excavated cavities. Our results highlight the importance of old-growth forest stands, tree decay processes and habitat legacies for securing a continuous supply of a keystone habitat resource for tree cavity-using wildlife in a global biodiversity hotspot of South America. Abstract in Spanish is available with online material.
... However, despite their threatened status, little is known about the size of parrot populations in the wild (Marsden & Royle, 2015), their habitat requirements (Snyder et al., 2000) or the seasonality of these requirements (Renton, 2002). Parrot habitat is defined by a number of limiting factors, namely food (Saunders, 1990;Berg, Socola & Angel, 2007), nest sites (Beissinger & Bucher, 1992;Wiebe, 2011), roost sites (Chapman, Chapman & Lefebvre, 1989) and water and mineral licks (Lee et al., 2010). However, the availability of these resources can vary significantly in space and time, and over the annual cycle parrots may require a variety of habitats and forest types (Renton, 2002;Marsden & Pilgrim, 2003). ...
Article
Populations of Psittacidae are endangered by habitat loss and the international pet market. The grey parrot (Psittacus erithacus) is among the most traded species, yet little is known about densities and their variability in time and space. The population of grey parrots on the island of Príncipe (Gulf of Guinea) was estimated with distance sampling, in both pre- and postbreeding seasons. Abundance was related to a range of habitat features using generalized additive models. Densities averaged 48 ± 3 (SE) individuals km⁻² in the prebreeding and 59 ± 4 in the postbreeding season, both extremely high compared to elsewhere in Africa and to other parrot species. Despite a population of 6000–8000 individuals over only 139 km², parrots were patchily distributed, being unrecorded in ~25% of surveyed areas. Abundance varied seasonally, with densities being significantly higher in secondary compared to primary forest in the post- but not in the prebreeding season. Abundance was most tied to the presence of nest-tree species prior to breeding and to feeding-tree species and lightly sloping ground after breeding. These results highlight the need to preserve a matrix of habitat types to provide resources for parrots across seasons and ensure that surveys recognize seasonality in habitat use as a potential bias.
... Nest-site availability may constrain breeding populations and reproductive success in cavity-nesting birds, [17][18][19][20] and thus the usurpation of nest cavities by Africanized honey bees could negatively impact them. This is a matter of concern for parrots (Order Psittaciformes), which are mostly obligate cavity-nesting species, and many are threatened with extinction. ...
Article
Invasive Africanized honey bees potentially compete with cavity‐nesting birds in South America. However, the impacts caused by this competition and its conservation consequences to threatened species are poorly known. We quantified the presence of these bees and assessed its competition for cliff cavities used by nesting Lear's macaws Anodorhynchus leari , a globally endangered parrot endemic to the Caatinga biome of Brazil. We treated bee hives with permethrin by shooting them with a crossbow bolt which distributed the compound upon impact. When feasible, we removed the comb and applied an insecticide (fipronil) to deter bee recolonization. We subsequently surveyed the macaw breeding population to verify whether our treatment allowed for the nest recruitment in cavities previously occupied by bees. We recorded >100 bee hives in the nesting cliffs. Hives outnumbered the macaw nests tenfold in two areas recently recolonized by the macaws. Cavities occupied by bees were significantly higher than those occupied by macaws, suggesting macaws may be forced to breed in lower cavities. None of the untreated bee‐cavities (n = 50) were occupied by nesting macaws, while 15% of treated cavities (n = 52) were occupied within two years post treatment. Treated cavities occupied by macaws were significantly higher than those not occupied. Hive management was responsible for 71% of the macaw breeding population increase. Experimental hive treatments were effective in restoring nesting resources lost due to bee infestation. An intensive and continued eradication program is recommended to enhance macaw's habitat restoration, facilitating its expansion into historical areas.
... Nest-site availability may constrain breeding populations and reproductive success in cavity-nesting birds, [17][18][19][20] and thus the usurpation of nest cavities by Africanized honey bees could negatively impact them. This is a matter of concern for parrots (Order Psittaciformes), which are mostly obligate cavity-nesting species, and many are threatened with extinction. ...
Article
BACKGROUND Invasive Africanized honey bees potentially compete with cavity‐nesting birds in South America. However, the impacts caused by this competition and its conservation consequences to threatened species are poorly known. We quantified the presence of these bees and assessed its competition for cliff cavities used by nesting Lear's macaws Anodorhynchus leari , a globally endangered parrot endemic to the Caatinga biome of Brazil. We treated bee hives with permethrin by shooting them with a crossbow bolt which distributed the compound upon impact. When feasible, we removed the comb and applied an insecticide (fipronil) to deter bee recolonization. We subsequently surveyed the macaw breeding population to verify whether our treatment allowed for the nest recruitment in cavities previously occupied by bees. RESULTS We recorded >100 bee hives in the nesting cliffs. Hives outnumbered the macaw nests tenfold in two areas recently recolonized by the macaws. Cavities occupied by bees were significantly higher than those occupied by macaws, suggesting macaws may be forced to breed in lower cavities. None of the untreated bee‐cavities (n = 50) were occupied by nesting macaws, while 15% of treated cavities (n = 52) were occupied within two years post treatment. Treated cavities occupied by macaws were significantly higher than those not occupied. Hive management was responsible for 71% of the macaw breeding population increase. CONCLUSION Experimental hive treatments were effective in restoring nesting resources lost due to bee infestation. An intensive and continued eradication program is recommended to enhance macaw's habitat restoration, facilitating its expansion into historical areas. This article is protected by copyright. All rights reserved.
... Место для устройства гнезда может оказаться более дефицитным ресурсом, чем место сбора корма. В частности, это известно для видов-дуплогнёздников (von Haartman, 1957;Newton, 1998;Wiebe, 2011). Когда и как молодые птицы собирают информацию об этих ресурсах? ...
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Foreign visitors to nest-boxes during breeding period and just after its termination were analyzed on the basis of data obtained in Moscow Region. Visual observations and video recordings at the nest-boxes with broods of either Pied Flycatchers (Ficedula hypoleuca) (n = 461) or Great Tits (Parus major) (n = 29) were made during June and July. In addition, in July and August, we recorded prints of claws of birds by means of strips of copy paper attached to empty nest-boxes at the entrance. The strips of copy paper on >100 nest-boxes were exposure in total for 1900 days. Juvenile Pied Flycatchers, Great Tits, Robin (Erithacus rubecula) and Wren (Troglodytes troglodytes) were detected among visitors of nest-boxes with broods of Pied Flycatchers. Nest-boxes with broods of Great Tits were attended only by adult Pied Flycatchers and by conspecific juveniles. In July, proportions of juveniles and adults were similar to each other. It was found that nest-boxes with broods were more attractive for visitors than empty ones. We suggest that inspecting of hollows helps young birds to assess the suitability of areas with hollows for choosing nesting sites in the future. Staying there for a sensitive period can increase the likelihood of the bird’s imprinting.
Article
Sexual selection, as a form of social selection based on reproductive resources, is a crucial driver of evolutionary change. Many studies on sexual selection identify potential targets only within the reproductive fraction of populations. Floaters constitute the non-territorial fraction of the population, according to the usual definitions. Floaters have been identified through exhaustive capture and marking programmes, removal and nest-box addition experiments, extra-pair paternity studies, acoustic marking and genetic studies. The literature shows that floaters may represent a considerable fraction of populations, especially among males. There is no clear evidence that size, condition or testosterone level is necessary for explaining floater status generally. However, the literature suggests that ornament size and expression are involved in territorial exclusion and may be either its cause or one of its consequences. There is some evidence that floaters survive and reproduce less well than territorials, and that changes from floater to territorial status are accompanied by changes in survival and reproductive rates. However, certain male floaters may obtain some reproductive success through extra-pair copulations. The possibility that floating constitutes a successful alternative strategy in some species cannot be excluded, although the current preliminary consensus is that floaters are 'making the best of a bad job'. Floater status may be imposed by limitations in the availability of mates or breeding space resulting in skewed population sex ratios, polygamous mating systems, high population densities and increased demand for specific breeding requirements such as space in colonies or adequate nesting cavities. Predictions concerning the effects of these factors have not been conducted to date. Few studies have been able to clarify the duration of floater status in any population. For short-lived species, floater status in a single breeding season may in fact imply zero lifetime reproductive success. In males, the existence of a considerable fraction of floaters attempting to breed may select for intense territorial behaviour and competitive mate guarding tactics in territory holders and in aggressive extrapair copulation and territory acquisition tactics in floaters. Interference competition from floaters may lead to density-dependent declines in reproductive success. In females, the attempts by floaters to attain breeding opportunities may have contributed to the observed propensities for female prospecting and for female-female aggression and the signalling of female dominance towards other females. Moreover, there may exist selection in females for signalling quality to mates in order to avoid being evicted by rivals. Excluding floaters from the analysis of sexually selected traits may severely affect sexual selection estimates because of biased sampling for large or more intensely expressed ornamentation. The importance of sexual selection may be negated or underestimated when in fact its action on floaters could be maintaining current levels of expression in the territorial fraction. Existing phenotypes should express, in their morphology, physiology and behaviour, the relentless drive through evolutionary time to avoid becoming a floater.
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Research Highlight: Trzcinski, M., Cockle, K., Norris, A., Edworthy, A., Wiebe, K., & Martin, K. (2022). Woodpeckers maintain the diversity of cavity‐nesting vertebrates in a temperate forest. Journal of Animal Ecology, https://doi.org/10.1111/1365‐2656.13626. Whether populations of hole‐nesting birds are limited by the availability of cavities is a long‐standing, fundamental question in avian community ecology. The structure of cavity‐nesting communities, known as nest webs, includes links between tree species that provide natural holes and bird species that nest in those holes (secondary cavity nesters, SCNs), tree species that provide substrates for cavity excavation and bird species such as woodpeckers that create cavities using those substrates (primary cavity nesters, PCNs), and between PCNs and SCNs. Trzcinski et al. (2022) focus on the latter links and provide the most compelling empirical evidence to date that cavities created by PCNs specifically, as opposed to natural holes or holes generally, limit populations of SCNs. Using data from a long‐term study, the authors employ three analyses to separate effects of availability of cavities from environmental factors such as food, habitat features and host tree abundance, while controlling for annual variation and autocorrelation within sites, to isolate the relationship between excavated cavities and SCN numbers. They show that nest density of SCNs is positively related to PCN nest density the previous year, an indicator of availability of excavated cavities, and that the effect of PCNs is stronger when other variables are accounted for. North American coniferous forests such as that studied by Trzcinski et al. (2022) are exceptional in that excavated cavities comprise the vast majority of nesting holes. Whether their findings apply to other systems in which PCNs are a major source of cavities, or to particular PCN–SCN relationships in systems in which excavated cavities account for a much lower proportion of nesting holes remains to be investigated. Nest webs describe the links between tree species that provide holes in which non‐excavating bird species (SCNs) nest and excavating species (PCNs) construct cavities, as well as PCN cavities used by SCNs. In some communities, most SCNs use natural tree holes (black lines), whereas in others, most SCNs depend on PCNs (red lines). Trzcinski et al. (2022) provide the best empirical evidence to date indicating limitation of SCN populations by PCNs in a community of the latter type.
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Nest box supplementation is widely used to increase nest‐site availability for cavity nesting animals, but the analysis of its effects on individuals breeding in natural cavities is often neglected. This paper offers a novel restoration technique to revert abandonment of natural breeding sites by a secondary cavity avian bird, the European roller (Coracias garrulus), and other ecologically similar species. We found that, after a program of nest box supplementation with ensuing monitoring, rollers gradually abandon nesting in natural and semi‐natural cavities in favour of nest boxes, because the latter are of higher quality. We examine whether reducing the entrance size of natural and semi‐natural cavities improves their suitability for rollers. A 6‐year program reduced the diameter of the entrance of sandstone cavities and cavities in bridges. This led to a high occupancy (59%) of manipulated nest‐sites. Manipulated sites were most frequently occupied by rollers and little owls (Athene noctua) (31% and 18% of sites, respectively). Manipulation did not affect clutch size or fledgling success. We suggest that nest‐site diversity and nesting in natural cavities should be preserved to reduce nest box dependence. Our study illustrates the value of nest boxes when used alongside restoration of natural breeding sites and provides insights for the management of natural cavities. This article is protected by copyright. All rights reserved.
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Bird species around the world are threatened with extinction. In North America, aerial insectivores are experiencing particularly severe population declines. To conserve these species, we need to know which life stages have the largest influence on population growth. We monitored a box-nesting population of Tree Swallows (Tachycineta bicolor) from 1975 to 2017. From this long-term dataset, we derived estimates of 9 vital rates: clutch size, reproductive attempts, and overwinter return for 2 age classes of adult females, and hatching, fledging, and juvenile recruitment rates. We conducted a life-stage simulation analysis on this population based on a 3-stage, female-based population projection matrix to determine which of these vital rates had the greatest influence on overall population growth rate. We determined each vital rate's sensitivity (i.e. the effect of a small change in each vital rate on population growth), elasticity (i.e. the effect of a proportional change in each vital rate on population growth), and ability to explain variation in population growth rate. Juvenile recruitment, female return for both age classes, and fledging success determine population growth because they have high sensitivity, elasticity, and explained large amounts of variation in population growth rate. Contrary to expectations, the number of nesting attempts, clutch size, and hatch rate have little impact on population growth rate. To stem Tree Swallow decline, and potentially the declines we see across the aerial insectivores, fledging success or overwinter survival must increase.
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Wood-pastures are disappearing rapidly in the eastern Mediterranean basin due to changes in land use. Traditional farming by means of goat husbandry and pollarding has allowed many trees to become old, creating valuable habitats for biodiversity. Developing viable management schemes for habitats of conservation concern require studies aiming at identifying relationships between habitat structure and associated species. In this study, the associations between habitat structure and bird species diversity were studied on a fine scale, using data obtained from transect inventories in an oak wood-pasture in southwestern Turkey. Almost all species were most abundant where trunk size, basal area or tree density peaked. Diversity of ground-nesters was slightly and positively associated with an increase in basal area. Low canopy-nesters were positively associated with an increase in shrub density, whereas there was a negative association for high canopy-nesters. Secondary cavity-nesters were unrelated to the density of small trunk cavities but exhibited a positive association with basal area of trees. Contrarily, primary cavity-nesters preferred trees with larger cavities, although this was most likely due to the presence of other desirable attributes of the very same trees. The results of this study give important insights to the structural and spatial organization of bird assemblages in a little studied but rich, culturally managed ecosystem in the Mediterranean.
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The overwhelming demand of deadwoods outside protected areas has not given deadwoods enough time to remain standing for the formation of the tree cavities by birds and other natural agents. Consequently, cavity adopter and large-bodied species face difficulties in finding and establishing acceptable nest sites. The focus of biodiversity conservation has been mainly within protected area systems, and less attention has been given to areas outside protected areas despite the fact that these areas support a bigger proportion of bird community. A high pace of deadwood loss on the entire landscape on the southern slopes of Mount Kilimanjaro is an irreversible situation in which is increasingly becoming a growing concern for the conservation of biodiversity beyond protected areas. Here, we investigate what extent deadwoods have in providing nest sites among cavity-nesting birds. We do this through observations and by placing artificial nest boxes on trees within three different land-use types. We found that deadwood volume and number of natural tree cavities were lower at coffee plantations as compared to mixed farming areas and Kilimanjaro National Park (KINAPA). Likewise, tree cavity positions from the ground were higher at coffee plantations than in other two land-use types. However, application of artificial nest boxes reveals that a good number of larger artificial nest boxes had greater occupancy, as did boxes placed at higher positions on trees from the ground at coffee plantations and mixed farming areas than at KINAPA, suggesting a shortage of natural cavity-nesting sites for larger birds and an avoidance of nest predation or human disturbances, respectively. Therefore, provision of artificial nest boxes could offer nesting opportunities for a range of cavity-nesting birds if designs and constructions take into consideration all possible factors that might hinder their occupation by cavity-nesting birds. In this manner, application of cavity nest boxes could be a vital alternative tool for conservation of cavity-nesting birds beyond boundaries of protected areas.
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Birds sing mostly to attract partners or to defend territories or resources. In relation to the first function, song can vary with age if older experienced males signal their quality through their vocal output. Regarding the second function, song can also vary with age if singing behavior helps mediate social interactions through repertoire sharing with neighbors. Here, we investigate whether song parameters change with age, and in which direction, in saffron finches Sicalis flaveola pelzelni, obligate secondary cavity nesters which produce elaborate melodious songs and show delayed plumage maturation. Cross‐sectional comparisons revealed that second year (SY) males sing shorter syllables, and shorter and less versatile songs than older after second year males (ASY), as expected if the latter are more experienced singers. Longitudinal comparisons, which better depict age‐related changes, showed that as birds age one year, song length and repertoire size do not change significantly, syllable duration shortens and, as expected for experienced singers, song versatility increases. Correlations between repertoire distance and nesting distance suggest that both SY and ASY males might be adjusting their repertoires to those of ASY neighbors; the former pattern conforms to the expectations if young birds try to emulate the songs of more experienced birds, while the latter is expected if song sharing helps de‐escalating antagonistic social interactions amongst males. This research, which provides the first description of song parameters in young second year saffron finches, expands our knowledge of song variation across age classes in songbirds. This article is protected by copyright. All rights reserved.
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Landscape modification is a major global threat to terrestrial biodiversity. Managing human-modified landscapes in ecologically sustainable ways is crucial to avoid and mitigate biodiversity loss. However, practitioners (e.g. policymakers and developers) still urgently require research to inform targeted habitat protection policies, on-the-ground land management practices, and biodiversity offset strategies. My research focused on identifying ways to strategically maintain and perpetuate habitat structures for wildlife in modified landscapes. I had three objectives: (1) measure and compare the current and future availability of habitat structures; (2) quantify the biodiversity value of scattered trees; and (3) test the effectiveness of artificial nest boxes as a biodiversity offset tool. First, I conducted vegetation surveys at 300 plots in three dominant landscape contexts (reserves, pasture, urban greenspace). I found that in urban greenspace, the availability of multiple habitat structures (e.g. trees, logs, shrubs) depended upon by biota were significantly reduced compared with reserves, but comparable with agricultural land. Using a simulation model for tree populations, I also found that hollow-bearing trees were predicted to decline by an average of 87% in urban greenspace over the next 300 years under existing tree management policies. I identified that only a combination of tree management approaches can arrest this decline. Second, I completed wildlife surveys at 72 individual trees of three sizes (small, medium, large) located in four landscape contexts (reserves, pasture, urban parklands, urban built-up areas). I recorded high invertebrate, bat and bird abundance and richness at scattered trees, representing a diversity of functional guilds. Furthermore, the biodiversity value of scattered trees in modified landscapes, including even small trees, was comparable or greater than that of trees located in reserves. I also found that several smaller trees could provide habitat compensation equivalent to that of a single large tree for some bird species and in certain landscape contexts (reserves and urban built-up areas). However, this was not a suitable offset strategy for a quarter of bird species and in other landscape contexts (pasture and urban parklands). Finally, I conducted an experiment using 144 nest boxes with different entrance sizes (20, 35, 55, 75, 95 and 115 mm), secured to trees of three sizes (small, medium, large) located in four landscape contexts (reserves, pasture, urban parklands, urban built-up areas). I found that adding nest boxes to large trees resulted in an increase in tree visitation by hollow-nesting birds. However, the same response was not observed at small, medium or control trees. Nest boxes were also only occupied by common native and exotic species and are thus unlikely to be effective at ameliorating the residual impacts of hollow-bearing tree removal, especially for threatened taxa. Based on my collective findings, I recommend: (1) adopting spatial zoning tactics that aim to resolve human-habitat conflicts and retain multiple habitat structures; (2) prioritising the conservation of scattered trees over the long-term by balancing both re-vegetation and mature tree preservation strategies; and (3) exercising caution in the wide-scale application of nest box offsets. These recommendations could assist practitioners in establishing more biodiversity-sensitive modified landscapes.
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Field voles Microtus agrestis were the owls' main food. Voles were abundant on afforested and replanted areas up to 15 yr after planting. Forty territories of tawny owl Strix aluco were located in one study area prior to 1979. All of these pairs bred in natural sites. In the first year (1980) that nest boxes were available 83% of the population switched to breed in them, and 100% by the fourth year. The number of occupied territories subsequently increased to 66 by 1990, and was attributed to an improvement in food supply resulting from clear-cutting. In another forest, barn owls Tyto alba declined as abandoned buildings became unavailable due to decay and renovation. Provision of nesting barrels led to a rapid increase in the breeding population, initially by yearlings reared on adjacent farmland. Nest boxes (barrels) were an essential element in conservation of barn owls in coniferous forests. In contrast to tawny owls, resident barn owls did not switch to nesting barrels. Therefore, in the early years of the study, breeding results may have been biased by a lack of breeding experience in most of the population. -from Authors
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Secondary cavity-nesting birds were studied in riparian habitat along the lower Colorado River, Arizona, to determine whether the birds were limited by availability of nest sites in relatively undisturbed habitat. Species differed in cavity use on the basis of size and time, and cavities were a limiting factor on only one of three study areas, but birds were responsive to cavity manipulations. Breeding numbers remained stable on an unmanipulated plot despite increased European starlings Sturnus vulgaris. Some cavity-related aggression occurred, but did not affect breeding numbers or success, because alternate nest sites were available.-from Author
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Breeding densities of secondary (i.e., nonexcavating) cavity-nesting birds are often assumed to be limited by availability of nest sites. We investigated this assumption for species breeding in northern Arizona' s ponderosa pine forests. In 1979, we installed nest boxes on three treatment plots that differed in habitat structure and monitored breeding densities of six species through the 1983 breeding season. The effect of nest boxes was evaluated by comparing breeding densities on three treatment plots from 1980 to 1983 with: (1) pretreatment densities (1973 to 1975, 1979), and (2) densities on control plots from 1980 to 1983. We observed variation in the importance of nest-site limitation among treatment plots and species. Overall breeding densities (all species combined) increased significantly on only two treatment plots. Individual species' responses were influenced by habitat structure, and breeding densities of only three species were apparently limited by nest sites before boxes were installed, Violet-green Swallows (Tachycineta thalassina), Pygmy Nuthatches (Sitta pygmaea), and Western Bluebirds (Sialia mexicana). A given species' breeding density in northern Arizona is nest-site limited if it is locally common and reliant on dead trees for nest sites. Availability of food or foraging substrate and territoriality may determine an upper limit to breeding densities if nest sites are in ample supply.
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We investigated the influence of disturbance type (agriculture and silviculture) within forested landscapes, amount of forest cover within 1 km of the site, and local habitat characteristics on the pairing success of Ovenbirds (Seiurus aurocapillus) in central Pennsylvania during May and June 1998. Because areas with low pairing success often are inferred to have high nest predation, we also examined whether pairing and nesting success were correlated across sites. We determined the pairing status of 116 male Ovenbirds on 10 sites within contiguous mature forest. Percent of males that were paired on each site ranged from 54–92% (mean = 78%). Pairing success was negatively associated with forest cover within 1 km and positively associated with leaf litter depth. Percent bare ground also was positively correlated with forest cover within 1 km of the site. Estimates of pairing success were unrelated to Ovenbird nesting success at each site (based on 48 nests), which suggests that site-level differences in nest predation or reproductive potential are not necessarily associated with the ability of males to acquire mates. Our data suggest that pairing success of Ovenbirds in forested landscapes is not reduced by the amount of habitat loss within 1 km and is determined by local habitat rather than landscape characteristics.
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Resumen. – Aves que anidan en huecos en bosques Neotropicales: los huecos como un recurso potencialmente limitante. – Frecuentemente se asume que las aves que nidifican en cavidades pueden estar limitadas por la presencia de sitios de nidificación. Sin embargo la mayoría de los estudios que apoyan la limitación de sitios de nidificación han sido realizados en paisajes modificados por actividades humanas de Norteamérica y Europa. Tanto en bosques maduros como en bosques degradados del Neotrópico, se sabe muy poco sobre la ecología y la disponibilidad de cavidades para este grupo de aves. Aquí revisamos artículos publicados y presentamos cinco estudios de casos que examinan la disponibilidad de cavidades, las limitaciones potenciales sobre las poblaciones, el reuso de cavidades y las relaciones entre especies de aves que nidifican en cavidades en cinco hábitats de tipo boscoso de América Central y América del Sur. No encontramos evidencia conclusiva de limitación de cavidades en bosques no perturbados sub-tropica-les, en los cuales una gran cantidad de cavidades estaban disponibles, pero no fueron utilizadas. Sin embargo, las cavidades no utilizadas difirieron de las cavidades con nidos activos, mostrando que es impor-tante considerar la calidad de las cavidades al determinar la disponibilidad y limitación de éstas. Además, uno de nuestros estudios de caso no mostró evidencia de competencia por interferencia por cavidades a ______________ 9 Current address:
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Why avian colonies vary in size and how food competition among nearby colonies a¡ects o¡spring quality are still not completely understood. We simultaneously examined the e¡ects of four scales of breeding density on two measures of o¡spring viability (body condition and T-cell-mediated immunity) in the colonial Magellanic penguin. Body condition of £edglings was inversely correlated with breeding density within 100 m 2 of nests, and decreased with increasing numbers of breeding pairs competing within the parental foraging ranges (100 km), probably as a result of density-dependent food depletion. The T-cell-mediated immune response was positively correlated with body condition, re£ecting, to some extent, the previous breeding-density e¡ects, and was negatively correlated with colony size, which may be related to social stress. However, given the e¡ect of protein intake on cell immunity, this result could also indicate a thus far neglected cost of coloniality, namely the consumption of low-protein food to compensate for the depletion of optimal prey. These results were not in£uenced by other traits, nor by the current exposure of birds to parasites and diseases, as measured by serological variables. Since body condition and the T-cell-mediated immune response of £edgling birds are indicators of their survival and recruitment prospects, the costs we have identi¢ed can explain variability in colony size in relation to food competition with surrounding colonies, as well as the skewed distribution toward small colonies in this species.
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We compared cavity-nesting bird communities in aspen (Populus tremuloides) woodland fragments classified on the basis of vegetation structure (tree density) and landscape context (surrounding vegetation). We found very few cavity nesters in fragments predominantly surrounded by forests. Fragments adjacent to meadows contained more species and a greater abundance of cavity nesters. Species richness and abundance were higher in sparsely than in densely treed meadow fragments. Because secondary cavity nesters are often limited by cavity availability, we augmented natural cavities with nest boxes. Although only five boxes contained bird nests, these were all in sparse aspen fragments predominantly surrounded by meadows. However, we found 25 northern flying squirrel (Glaucomys sabrinus) nests in boxes, none of which were in sparse meadow fragments. In addition to high-lighting the importance of landscape context in avian and mammalian habitat relationships, our results suggest that predator or competitor interactions may help structure this cavity-nester community.
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The breeding densities of many bird-species which nest in tree cavities are in some areas limited by shortage of sites. This is evident from circumstantial evidence in which the numbers of breeding pairs in different areas correlate with the numbers of local nest sites, or where changes in the numbers of nest sites resulting from natural processes or human action are followed by changes in the numbers of pairs. It is also shown experimentally, where nest site provision or removal has been followed by a corresponding change in breeding density.
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We compared cavity-nesting bird communities in aspen (Populus tremuloides) woodland fragments classified on the basis of vegetation structure (tree density) and landscape context (surrounding vegetation). We found very few cavity nesters in fragments predominantly surrounded by forests. Fragments adjacent to meadows contained more species and a greater abundance of cavity nesters. Species richness and abundance were higher in sparsely than in densely treed meadow fragments. Because secondary cavity nesters are often limited by cavity availability, we augmented natural cavities with nest boxes. Although only five boxes contained bird nests, these were all in sparse aspen fragments predominantly surrounded by meadows. However, we found 25 northern flying squirrel (Glaucomys sabrinus) nests in boxes, none of which were in sparse meadow fragments. In addition to highlighting the importance of landscape context in avian and mammalian habitat relationships, our results suggest that predator or competitor interactions may help structure this cavity-nester community. Composición de las Comunidades de Aves que Nidifican en Cavidades en los Fragmentos de Bosque Montano de Álamo: El Papel del Contexto del Paisaje y la Estructura del Bosque Resumen. Comparamos comunidades de aves que nidifican en cavidades en fragmentos de bosque de álamo (Populus tremuloides) clasificados en base a la estructura de la vegetación (densidad de árboles) y al contexto del paisaje (vegetación circundante). Encontramos muy pocas aves que nidifican en cavidades en los fragmentos rodeados predominantemente por bosque. Los fragmentos adyacentes a prados presentaron más especies y mayor abundancia de aves. La riqueza y la abundancia de especies fueron mayores en fragmentos con baja densidad de árboles que estuvieron rodeados por prados. Debido a que las aves que nidifican en cavidades secundarias están a menudo limitadas por la disponibilidad de cavidades, aumentamos las cavidades naturales con cajas de anidaje. Aunque solamente cinco cajas contuvieron nidos de aves, éstas estuvieron todas en los fragmentos con baja densidad de álamos rodeados predominantemente por prados. Sin embargo, encontramos 25 nidos de ardillas voladoras norteñas (Glaucomys sabrinus) en las cajas de anidaje, de las cuales ninguna estuvo en fragmentos con baja densidad de árboles rodeados por prado. Nuestros resultados destacan la importancia del contexto del paisaje en las relaciones entre el hábitat y las aves y mamíferos, y sugieren que las interacciones con depredadores o competidores pueden influenciar la estructura de la comunidades de aves que anidan en cavidades.
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Territory settlement by juvenile male Parus major in September, the crucial period for territory density in years with a seed food supply in winter, appeared to be independent of the presence of nestboxes. Density of newly settled territories was determined by the density of adult territory owners and juvenile nonterritorial males. Occupation of vacant areas during winter and spring depended on the presence of nonterritorial birds. Marked shifts in the position of the area were only observed in males with territories in subareas without nestboxes and were directed towards areas with an excess of nestboxes. Earlier experiences with these boxes for breeding and roosting seemed to be important. Most territory owners in areas without boxes roosted from October onward outside cavities in their territories. While in areas with nestboxes all territorial pairs used them for breeding, most of the territorial pairs from areas without nestboxes made breeding attempts in nestboxes outside territories and outside the area. Local survival rate of territory owners was markedly lower in areas without nestboxes, due to emigration in summer and winter and to mortality in winter caused by predation, competition for nestboxes and unfavourable weather conditions. -from Author
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We investigated the influence of disturbance type (agriculture and silviculture) within forested landscapes, amount of forest cover within 1 km of the site, and local habitat characteristics on the pairing success of Ovenbirds (Seiurus aurocapillus) in central Pennsylvania during May and June 1998. Because areas with low pairing success often are inferred to have high nest predation, we also examined whether pairing and nesting success were correlated across sites. We determined the pairing status of 116 male Ovenbirds on 10 sites within contiguous mature forest. Percent of males that were paired on each site ranged from 54-92% (mean = 78%). Pairing success was negatively associated with forest cover within 1 km and positively associated with leaf litter depth. Percent bare ground also was positively correlated with forest cover within 1 km of the site. Estimates of pairing success were unrelated to Ovenbird nesting success at each site (based on 48 nests), which suggests that site-level differences in nest predation or reproductive potential are not necessarily associated with the ability of males to acquire mates. Our data suggest that pairing success of Ovenbirds in forested landscapes is not reduced by the amount of habitat loss within 1 km and is determined by local habitat rather than landscape characteristics.
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Cavity-nesting birds that excavate nest holes may be limited by the availability of suitable substrates for excavation. Suitability of trees for excavation may be influenced by substrate hardness and excavation strength of the bird. Excavation strength, in turn, may vary among bird species, causing nest-tree selection to vary among excavator species. We examined use of quaking aspens (Populus tremuloides) for nest trees as a function of tree hardness in four species of woodpeckers: Williamson's Sapsucker (Sphyrapicus thyroideus), Red-naped Sapsucker (S. nuchalis), Downy Woodpecker (Picoides pubescens), and Hairy Woodpecker (P. villosus). Hardness of trees was measured at 95 nest trees, 94 neighboring trees, and 150 random trees using a new technique described here. Other investigators have speculated that the gross external appearance of trees/snags can be used to estimate hardness. Hardness decreased from live trees to partly dead trees to dead trees and with increasing height in trees, but hardness was not related to other external features such as numbers of conks or percentage of the tree covered with bark. All four bird species chose nest trees that were softer than neighboring or random trees, and nest trees were softer at nests than at other heights measured. The four species selected trees of different hardness for nesting; Red-naped Sapsucker and Hairy Woodpecker chose harder trees than Williamson's Sapsucker and Downy Woodpecker. These results suggest that primary cavity nesters are sensitive to subtle characteristics of trees that reflect hardness, some of which may not be apparent in the external appearance of the trees.
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(1) Buffleheads (Bucephala albeola) are cavity-nesting ducks that are highly territorial during the nesting period. We tested whether nest-site availability or territorial behaviour limits breeding density. (2) The number of suitable cavities was two to three times higher than the number of breeding pairs during all 4 years. (3) Added next boxes, used increasingly by buffleheads as the study progressed, were compensated for by a concomitant decline in the number of natural cavities used. (4) The number of breeding pairs remained stable throughout the study. There was, however, a surplus of adult males in the population, and possibly also a surplus of adult females. (5) We removed seven territorial males during the nesting season. There were four replacements, three by previously unmated males and one by a new pair. (6) We conclude the nest sites are not limiting for buffleheads in the Cariboo Parkland, BC, but the territorial behaviour may limit breeding density in this population.
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A number of analogous (convergent) adaptations occur in hole-nesting birds. Their main causes are the safe nesting sites and the keen competition (both intra- and interspecific) for them. Competition has caused certain characteristics in behavior, such as development of territorial behavior only after finding a suitable hole, fighting for a nesting-hole instead of for a territorial area, and the male's demonstration of the nesting-hole in courtship-display. The safety of the nesting site has caused other adaptations, such as frequent polygamy, hissing notes in incubating adults and in the young, lack of cryptic color in the eggs, large clutch size, and slow development of eggs and young. A long period of evolution is needed, however, before a species is able to take full advantage of the safety of the nesting site. In primary hole-nesters the adaptations are much more clearly developed than in secondary hole-nesters. Tits, for instance, have maintained spotted eggs, open-nesting Parrots white eggs. The Pied and Spotted Flycatchers have nearly identical growth curves in the young, in spite of the one having very safe and the other very unsafe nesting sites, and so on. The number of subspecies was found to show a positive correlation to clutch size (hence, hole-nesting birds tend to have larger number of subspecies). This may be due to stronger selection in species with more offspring, and/or the fact that species with large clutches are relatively often non-migratory.
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We examined the relationship between nest site availability and density of secondary cavity-nesting birds by blocking cavities in an oak-pine (Quercus spp.-Pinus sp.) woodland. In 1986 and 1987 we blocked 67 and 106 cavities, respectively, on a 37-ha plot. The combined density of secondary cavity-nesting birds did not decline in either year by a greater proportion on the treatment plot than on a control plot, indicating that cavities were not limiting. In habitats where timber management has not substantially reduced availability of natural cavities, managers should not assume nest site limitation; natural nest site availability should be evaluated before implementing nestbox programs designed to increase populations of secondary cavity-nesting birds.
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A nest-box experiment was carried out in rich subalpine birch forests, Swedish Lapland. During a six-year period the passerine bird density in an area (23 hectares) with a surplus of nest-boxes was compared with the density in a control area (29 hectares) without boxes. A large number of the nest-boxes were occupied by one species, the Pied Flycatcher, increasing the bird density in the nest-box area by about 75 per cent. This immigration of the flycatcher did not cause a demonstrable change in the population numbers of the other species. The year to year fluctuations of the flycatcher numbers were in accord with the fluctuations of the other species taken together in the same area and also with the fluctuations of the bird numbers in the control area. The result of this investigation is compared with that of a similar experiment in Southern Sweden.
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Use of 235 nesting boxes by birds and mammals was compared to use of 165 natural cavities in 3 forest habitats. Nest boxes were used more frequently than natural cavities by 12 of the 19 species using cavities (P
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The differences in density of juveniles in oak-rich and adjacent other habitats on 1 September are much larger than can be expected from the reproductive rates and the total survival rates. This is mainly a result of dispersal by broods in the dependent period. Any differences in juvenile density at 1 September will be found back in differences in territory density in autumn and hence in spring.- from Author