As part of a recovery plan of the species two feeding stations have been implemented on the island, where up to 150 marked individuals can be observed on a single day. Birds visiting the feeding station are completely at ease, allowing detailed observations on many aspects of their usually highly secret life. While the vultures are essentially attracted to the food, they also use these sites to engage in most of their other daily activities. An extensive data set on social status was collected of birds visiting the feeding station showing females to be the dominant sex, but with a relatively strong linear dominance hierarchy also being present within each sex (i.e. based on 4,593 displacements between 141 individuals during 400 h of observation. Data on social behaviour was combined with a high-resolution GPS data obtained from 45 individuals tracked for 1 year (± 1 million data-points).
Individual vultures were found to be highly repeatable in their time spent at sites where carcasses were supplied at predictable or semi-predictable rates (central feeding station vs. farms). Despite high levels of repeatability found for monthly home range size, and to a lesser extent, flight activity, mobility traits did not correlate with resource preferences at the between-individual level, implying that individuals did not exhibit consistent differences in food searching strategies in relation to their degree of resource specialization. By contrast, resource use and mobility parameters varied plastically within individuals on the short-term, with birds having larger home ranges and low flight activity in months where individuals spent relatively more time at the feeding station, but not at farms. Social dominance appeared an important individual-level predictor or resources preferences. In this system with reversed sexual size dimorphism, the dominant sex (females) preferred carcasses provided at the predictable feeding station, while males preferred carcasses provided at farms. However, within territorial males and females, a reversed effect of social status on resource use was found, showing a positive correlation in females, while a negative correlation was found in males. In territorial females, but not males, dominant birds bred closer to the feeding station, suggesting spatial constraints through central place foraging task to affect resource use patterns in this sex. Year-round analyses of the relationship between social status and mobility revealed several seasonal association that varied according to sex and territorial status, but only during specific parts of the year.
Apart from analysing individual space use patterns and foraging behaviours, more general aspects of the behavioural ecology of vultures were described. Basic information on sociality within vulture societies is still lacking for most, if not all species, hampering the full evaluation of the social consequences of vultures declines. Taking advantage of the unique properties of the study population, novel socialising behaviours were discovered and the causes and consequences of polygyny and polyandry analysed. Lastly, while performing fieldwork, it was noticed that individuals often display remarkable variation in reddish coloration on parts of their neck and head. By providing red mud at the feeding station, it appeared that this reddish colouration was the result of birds deliberately staining their feathers with red soil. Videos of this behaviour were the first ever recorded and reached the worldwide media.
