Environmental Drivers of Communal Roost Distribution and Size in Western Jackdaws (Coloeus monedula) Under Landscape Transformation.

Abstract

Large-scale studies linking species distribution to environmental variables are crucial for understanding human impacts on ecosystems and informing conservation actions. Multiscale habitat models reveal how organisms interact with their environment and respond to pressures like habitat loss and urbanization. This study investigates the environmental drivers influencing the winter distribution and abundance of the Western Jackdaw (Coloeus monedula) across the Iberian Peninsula, highlighting its value as a model for assessing anthropogenic impacts. Using data from a coordinated winter census of communal roosts, we employed a multiscale analytical framework to analyze roost location and size. Environmental suitability models were developed to identify potential roosting and foraging areas, with particular emphasis on the role of urbanization in shaping the species' distribution in winter. Urban areas and th composition of agricultural landscapes emerged as key determinants of roost location, positively influencing both roost occurrence at fine scales and habitat suitability across foraging areas. Conversely, high vegetation productivity and dense vegetation cover negatively impacted roost size, suggesting that communal roosting patterns are heavily dictated by the proximity and quality of foraging grounds. Suitability models identified urban areas, agricultural landscapes, and river valleys as the most favorable habitats. Nevertheless, urbanization significantly constrained overall suitable habitat extent. These results reveal an emerging urban commuting strategy where individuals decouple nocturnal safety in urban refugia from diurnal foraging in agro-pastoral habitats. This behavioral shift helps explain widespread declines of common species, as rising energetic costs of balancing anthropogenic safety and resource availability may drive population instability in the Anthropocene.