New Insights into the Cosmetic Behaviour of Bearded Vultures: Ferruginous Springs Are Shared Sequentially

SIMPLE SUMMARY: The adventitious nature of the rufous colour of bearded vultures was first suggested in the XIXth century, and proved conclusively almost a century later. However, for more than 20 years, no advances about this mysterious behaviour have been made, and observational studies are needed to discover its function. Here, with the help of camera-traps and GPS transmitters we provide new observations about the regular use of a ferruginous spring situated in the Spanish Pyrenees by the species, providing new insights on the behavioural ecology of bearded vultures. ABSTRACT: Different hypotheses have been proposed to explain the function of cosmetic behaviour of bearded vultures, being the signalling individual dominance status the most accepted. However, no advances have been made in understanding this mysterious behaviour, in part due to the secrecy of this species. With the help of camera traps and GPS devices we monitored the use of a ferruginous spring in the Pyrenees (Spain) providing new insights into this aspect of their behavioural ecology. Most of the visits (93.5%) involved a single bearded vulture and bathing behaviour only occurred when a single individual was present, confirming their secretive behaviour. A total of 50% of individuals that visited the site were non-adults, suggesting that cosmetic coloration functions as an attenuating signal that may also benefit subordinate individuals. Future studies with the help of new technologies could help to disentangle some questions about the real function of cosmetic coloration and their social relevance.