Adult Griffon Vulture wearing a UvA-BiTS logger, January 2013. (Photo: Christian Aussagel)

The Eurasian Griffon Vulture Gyps fulvus is one of the largest raptors in Europe, with a wingspan of 2.5-2.7 meters and a body mass of 8-10 kg. Both sexes have a similar appearance and adult birds can be distinguished from immature by the clear color of the ruff, beak and eye. They are long-lived birds with an average life expectancy of 28 years.

They live in mountain ranges around the Mediterranean and breed on cliffs. The pair is generally faithful for life and the breeding season starts in December with display behavior. They lay one egg every year in January-February. After 60 days incubation, the egg hatches in March-April. The chick is fed by both parents until fledging in July-August, then it stays in the vicinity of its parents, being fledged at the nest, until emancipation in October. The juveniles are erratic until their sexual maturity at the age of 4. Being philopatric, most will breed in the colony where they are born. Indeed Griffon Vultures are unusual among raptors since they are highly social birds, breeding in large colonies as well as feeding in groups.

Adult Griffon Vulture in flight in the Jonte valley, November 2005. (Photo: Olivier Duriez)

Vultures are masters of soaring flight: their large size prevents sustained flapping flight. Therefore they make use of ascending air currents, provoked by wind on relief or by thermals. They commonly reach altitudes of several thousand meters where they are able to locate their food: ungulate carrion. Vultures are considered the only obligatory scavengers among vertebrates. Scavenger raptors are declining worldwide, and their disappearance (e.g. in India since 2000), which cause sanitary catastrophes as well as the proliferation of rats and stray dogs, remind us of their ecological significance.

Griffon Vultures evolved in Europe as commensal of extensive farming. In order to find carrion spread over in the environment in a spatially and temporally stochastic way, they developed social foraging strategies. In particular, the attraction of searching individuals by feeding conspecifics seems to enhance their search efficiency. However, questions remain about the importance of individual and social contribution in the success of prospection behaviour, i.e. before a carrion is discovered. Three hypotheses prevail: 1) vultures disperse at random, with the constraint of topographical features that create ascending currents necessary for soaring flight; 2) vultures use personal knowledge of food availability and visit, in priority, places with higher probability of finding carrion; 3) vultures forage in an actively formed network, being regularly interspersed and observing the behavior of other flying vultures, in order to aggregate quickly when carrion is found.