Seasonal dynamics in the exploitation of natural carcasses and supplementary feeding stations by a top avian scavenger

Abstract

Supplementing vulture populations with carcasses disposed at feeding stations is a common management and conservation practice worldwide. However, there is a lack of knowledge on the dependence of large vultures on the supplementary feeding stations (SFS) in areas with high abundance of natural food. We tagged 11 Griffon Vultures (Gyps fulvus, Hablizl 1783) with GSM/GPS transmitters in the Eastern Rhodopes, Bulgaria and studied the seasonal dynamic of feedings at SFS and at occasional carcasses found in the field. We used combination of remote sensing and field inspections to identify the vulture feeding events. Our results show that most of the feeding events occurred at occasional carcasses found in the wild (77.4%), whereas only 22.6% were at SFS, but high seasonal variation was observed. Vulture’s reliance on feeding stations was lowest in summer (19.82 ± 7.8%) and highest in winter when 56.5 ± 16.1% of the feedings were at the SFS. Griffon Vultures travelled longer daily distances in days feeding in the wild compared to days when they were not feeding or were visiting SFS. Our study indicates that in habitats with high abundance of natural food (free-range livestock and game), vultures tend to actively forage and use feeding stations as supplemental sources of food, mostly during long periods of adverse weather or in winter when foraging conditions are worse and natural food is less abundant.