Canarian Egyptian vultures are a remarkable species displaying an unusual and rich behavioural repertoire. Over the past years, we gained detailed knowledge about their social lives because complex behaviours can readily be observed at one of the feeding stations located in the centre of Fuerteventura. Surplus food provided at this site (mainly pig heads), offers excellent opportunities for data collection on dominance because all birds are individually marked. Apart from food acquisition, this site is also an important place where vultures socialize, especially outside the breeding season.

Social dominance

Through extensive observations of feeding vultures, we gained highly detailed knowledge about the social structure of this insular population. As only one individual feeds at a single pig head at each point in time, it is relatively easy to score competitive displacement and movement of individuals between pig heads. Normally, high-ranked individuals displace low-ranked individuals by means of a small kick or brief peck, though non-contact displacement is also common. Preliminary analyses of competitive displacement data collected between 2016-2017 show that females are dominant over males, and that non-territorial and young individuals have lower ranks, however, rank simultaneously increases with age. Analyses are based on 4593 displacements between 141 individuals (~50% of the total population, >70% of (sub)adults, i.e. > 2 years) involved in >20 displacements (average 65.1 ± 3.0 S.E., range 20–175)

Overall low-levels of aggression during food exploitation and well-respected dominance relations suggest the existence of high-levels of indivual recognition, possibly facilitated by their distinct yellow and wrinkeld faces, as well as basic rank-assesment skills. For example, during feeding, individuals often first look around to specifically select a lower ranked individual to be displaced. Conflicts are sometimes settled through ritualized dominance displays, whereby birds parade face-to-face with erected head feather. These displays may help to settle conflicts with unfamiliar individuals and/or specifically for rank establishment.

Escalated flights, although rare, typically attract the attention of conspecifics. The photo below shows a fight between two adult females outside the breeding season, with the female on top displaying a dominance posture. Intriguingly, bystanders sometimes start to peck on the defeated individual. These observations suggest vultures keep track of shifts in social rank and/or social disputes, possibly to use such information in future contest and/or for strategic rank-optimization.

As opposed to mainly Egyptian Vultures and other vulture species, Canarian Egyptian Vultures do not provide post-fledging care. Soon after fledgling, most juveniles can be seen at the central feeding stations, where they interact and fight with other juveniles and even adults. This suggest they learn social skills independent of their parents.

Allopreening

Allopreening is a common social activity displayed by pair members in a wide range of bird species. It is well recognized that allopreening activity plays an important role in maintaining pair bonds. However, an interesting phenomenon observed in Canarian Egyptian Vultures is that allopreening also frequently takes places outside a pair-living context. These allopreening activities can take place between adult and immature birds, members of different pairs, and same-sex individuals, especially between females, and very rarely, also males.

The photos below show two preening females (left panel) and a paired female preening a paired male.In the majority of cases, allopreening is non-reciprocal, i.e., one individual preens the other and the preened individual decides when it should stop by pecking. Curiously, while drinking or bathing, individuals may often suddenly stop their activities and start to preen a recent visitor, as shown below.

During encounters, allopreening can be elaborate, but sometimes also just involve a brief contact as shown below

Why these birds preen each other is unclear. Allopreening may primarily serve a function in mate-seeking or evaluation, or be a means by which paired birds attract an additional partner, given the relatively high frequency of polygynous and polyandrous trios in this population (ca. 10% of pairs). However, the reason why individuals of the same sex preen each other is more difficult to understand. An interesting observation in this context are two females, both carrying GPS-trackers, that temporally engaged in joint activities during the breeding season. In the last week of April 2016, a 7-year unpaired female visited the territory of a pair with a small chick. Strangely enough, both females started to make long-distance flights together on several days (see panel 1 and 2 below). On the 3rd of May, both birds flew to the south of Fuerteventura, where they eventually split, with the ‘previous’ visitor flying to the feeding station in the north of the island. We currently have no clear explanation for this peculiar behaviour, but it fits the general notion that these birds have a hidden social life we still very poorly understand