Implications of nest-site limitation on density-dependent nest predation at variable spatial scales in a cavity-nesting bird

摘要

Nest-site limitation may have different implications in the spatial distribution of breeding pairs depending on the availability of suitable habitat and the types of nest-sites. Distribution of cavities suitable as nest sites may allow circumstantial aggregation or active choice of colonial nesting, which may have different implications on breeding performance through effects on breeding density, with variable costs and benefits depending on the consequences of intraspecific competition, social interactions and predation. We evaluated the effects of breeding density derived from nesting site limitation on breeding performance and predation at different spatial scales and considering multiple social, population and environmental limiting factors in the red-billed chough Pyrrhocorax pyrrhocorax. The results indicate that variable breeding density may arise within the population depending on the availability and spatial distribution of nest-sites. Nest-site availability and distribution may also determine social breeding systems (isolated or aggregated) at variable densities, thus resembling differences found at different spatially distant populations under contrasting environmental conditions. Breeding performance was related to density-dependent processes of population regulation, especially density-dependent nest predation due to predator attraction to nest clusters. Results also indicate that predation pressure depend on density patterns at large scales. This suggest that predation may have important consequences on population dynamics of spatially structured populations depending on the strength of this kind of density dependence, which in turn may depend on habitat features affecting the prey but also the spatially variable guild of predators. Because habitat and nesting site availability may vary spatially depending on multiple human influences, understanding the strength and form in which breeding density and nest predation at different spatial scales may influence the size and persistence of populations can help to manage them more adequately.