Long-term anthropogenic drivers of diet composition and niche breadth in an endangered avian scavenger: The scant role of sanitary regulations

The widespread and accelerated transformation experienced by our planet results in populations of endangered species having to survive in highly-altered environments and increasingly relying on resources provided by human subsidies. Presently, vultures rank among the most imperiled functional groups of large vertebrates globally, a situation that is largely attributed to the rapid intensification of agriculture and the subsequent transformation of farming practices and agro-grazing landscapes. Hence, documenting the long-term fluctuations in the vultures’ dietary patterns in response to environmental changes, particularly in livestock management, is of utmost significance. Here, by means of bulk stable isotope analysis (δC and δN), we examined long-term variations in diet composition and niche breadth in a population of the endangered Egyptian vulture () in the north of the Iberian Peninsula. We specifically focused on the effect of European sanitary regulations enacted in 2014, which allow sheep farmers to abandon livestock remains for consumption by scavenging birds, except for pig carcasses. We found that the implementation of these new regulations did not cause a change in the diet of vultures. Changes were only detected in scrubland areas and were driven by an increase in the consumption of wild rabbit which, in turn, lead to expansion of the trophic niche. These results indicate that these endangered vultures are heavily dependent on food sources derived from intensive farming, mostly of pigs illegally disposed in the wild, and moreover, highlight the importance of carcasses of small vertebrates, often disregarded in conservation programs in favor of the contribution of livestock remains. Our research provides valuable insights into the spatiotemporal dynamics of trophic strategies among avian scavengers, specifically in the context of changes resulting from intensified human-pressures on agro-grazing Mediterranean landscapes.