Evidence for density-dependent habitat occupancy at varying scales in an expanding bird population

Understanding factors shaping the spatial distribution of animals is crucial for the conservation and management of wildlife species. However, few studies have investigated density-dependent habitat selection in wild populations in non-equilibrium conditions and at varying spatial scales. Here, we investigated density-dependent habitat selection at varying spatial scales in an increasing white stork Ciconia ciconia population using a long term data set in western France. During a 16-year study period, the breeding population density increased from 0.66 nests per 100 km2 to 6.6 nests per 100 km2. At the beginning of the colonisation of the area settlement probability of storks was mainly positively affected by grasslands located near wetlands. Areas with intensive or moderately intensive agriculture were extremely unlikely to be occupied by breeding birds. However, selection for the initially preferred habitats faded as stork density increased although the proportions of habitat types remained unchanged. At the same time selection for initially less favoured habitats had increased. Moreover, we found that the spatial scale of selection for each foraging habitat variable was consistent over time. Our results suggest that snapshot analyses of resource selection in populations at high density may be misleading for population conservation or management. In contrast, a longitudinal approach to resource selection can be a valuable tool for understanding resource limitation.