Age class and natal origin drive foraging patterns in a reintroduced Cinereous Vulture population

Lucy Mitchell , Luc Lens, Frederick Verbruggen, Juan José Iglesias-Lebrija, Émilie Delepoulle, Ernesto Alvarez, Pilar Oliva-Vidal, Antoni Margalida, Jorge Tobajas

Widespread vulture population declines are often counteracted by conservation strategies including reintroduction programs and supplementary feeding schemes. However, the role of supplementary feeding – focusing on specific, predictable, feeding sites - on movement behaviour, has been little explored, especially within populations in which reintroduced and wild born birds of different age-classes may show differing behavioural movement patterns. However, such information becomes crucial for improving conservation and management actions. We analysed GPS data from both reintroduced (n = 31) and wild born (n = 28) cinereous vultures Aegypius monachus in Catalonia, North-eastern Spain, collected during a long-term study (2009–2020), to assess SFS use patterns according to natal origin, release method, and age-classes of individuals. We found high age-related variation in SFS use; juveniles revisited fewer SFS, and spent much longer in these locations compared with immatures, subadults, and adults, pointing to a dependence of juveniles on social information, along with a lack of foraging and flight skills. Regular adult revisits to multiple SFS suggests that these vultures can develop a comprehensive spatial memory of SFS by adulthood. Additionally, birds that were released via an acclimatisation aviary showed lower affiliation with SFS compared with ‘hacked’ birds and wild-born nestlings perhaps suggesting a tendency to spend more time exploring the wider environment. Our study has particular relevance in light of the potential public health-related legislation changes within the European Union or the changes in management of SFS, which could alter movement patterns and demographic parameters of Iberian vulture populations.