Intra-specific competition in foraging Griffon Vultures Gyps fulvus: 1. Dynamics of group feeding

Abstract

Capsule Young Griffon Vultures Gyps fulvus suffer intense competition from elders at feeding sites and this reduces their intake rate. Aims To explore the costs and benefits of feeding in groups in Griffon Vultures Methods In a French population of individually marked vultures, we studied by video the dynamics of feeding events and the difference in competitive ability to access carrion between ages and sexes. Results When several carcasses were available, the distribution of the birds at the beginning of feeding event was generally different from an ideal free distribution. Depending on food availability, the potential group size was always higher than the maximum group size observed. However, the number of birds landed increased with food mass and was always higher than the potential group size, in accordance with the stable group size hypothesis. The timing of arrivals and departures of individuals differed with respect to their age, with old adults arriving and leaving before the arrival of other age-classes. Some birds, mostly old adults with a lower interaction rate, aggressiveness and dominance, regularly started the feeding events first. Conclusions At high-intensity feeding sites close to the colonies younger vultures probably access a lower quantity and quality of resources than old adults. © 2012 British Trust for Ornithology.