Vultures thrive on more than livestock: small wild vertebrate carcasses are key for nestling growth

Scavenging represents one of the least comprehensively understood ecological processes, despite growing research attention. Available knowledge is constrained by methodological limitations that frequently neglect the nutritional heterogeneity provided by carcasses of different species and tissue types. Carrion selection may thus depend not only on environmental factors but also on species-specific life-history traits. Here, we examine how carrion use by the globally endangered Egyptian vulture (Neophron percnopterus) varies throughout the breeding season, across a gradient of prey types ranging from livestock to small wild vertebrates. We analyzed bulk stable isotope values (δ13C and δ15N) in growing feathers of nestlings at the nest and assessed the influence of individual variables such as sex, age, and hatching order. Our results show that the consumption of small wild vertebrates is highest during early nestling development, likely driven by demand for micronutrients such as calcium during rapid skeletal growth. As nestlings mature, their diet shifts toward livestock carrion, particularly pig remains, likely supporting energy accumulation for fledging and post-reproductive migration. The trophic niche is broader early in development and narrows with age. These findings highlight a previously unrecognized temporal shift in diet that challenges conservation strategies relying solely on livestock carcass provisioning. Moreover, they may be relevant to other avian scavengers with similar ecological requirements. Overall, our study underscores the ecological importance of carrion diversity in shaping scavenger feeding strategies and has significant implications for conservation planning and ecosystem functioning.