Heterospecific visual cues and trophic facilitation processes used by a solitary bone-eating vulture

Abstract

While the influence of public information sharing on foraging strategies is of growing interest, empirical studies exploring intraguild social information use and facilitation roles between individuals with different trophic specializations remain scarce. Heterospecific facilitation should be more common in specialist foragers, for example, the bearded vulture Gypaetus barbatus, a solitary bone-eating scavenger. We monitored 133 carcasses of different types/sizes in open and shrubland landscapes in the Spanish Pyrenees to explore bearded vulture foraging in relation to social information transfer and adaptive trophic behavior. We hypothesized that they might (1) feed on carcasses after initial heterospecific exploitation; (2) use heterospecifics to locate and/or exploit carcasses; and (3) prefer old carcasses over fresh ones. We recorded bearded vultures scavenging at 44 carcasses; 95.5% had been previously exploited by heterospecifics (93.2% by griffon vultures Gyps fulvus and 2.3% by golden eagles Aquila chrysaetos) while only two small-sized carcasses were scavenged without previous heterospecific exploitation. Bearded vultures were not observed scavenging at carcasses used only by mammals. Both griffon and bearded vultures took longer to find carcasses in shrublands than in open landscapes. However, bearded vulture arrival times between landscapes after carcass discovery by griffon vultures were similar. Bearded vultures were more likely to discover a carcass the greater the number of griffon vultures exploiting it. Only 10.4% bearded vulture scavenging events occurred after the third week following heterospecific exploitation, suggesting that recently opened carcasses were preferred. Clearly, heterospecifics play an essential role in bearded vultures foraging success, and griffon vultures are fundamental facilitators for specialist foragers, both in providing visual cues to food location and in opening up carcasses to enable access to food.