Displays and vocalisations in the Palm-nut Vulture, Gypohierax angolensis

Abstract

The postural and auditory components of the behaviour depicted in the type illustration of Gypohierax angolensis are described and analysed. The display, here termed the forward-and-down display (FDD), was used by the female in territorial defence as well as when interacting with her mate and expressing dominance. The FDD is accompanied by a disyllabic vocalisation ûr-ûrrr (a bark followed by a prolonged growl), for which audiospectrographic analyses are presented. In the breeding male the first note was replaced with contact calls and the function of the display differed. The male gave the FDD when working on the nest cup and often in a context indicating he was trying to get the female to come for mating. Audiospectrographic analyses are presented for three other vocalisations: (1) guttural quacking sounds, kwuk-kwuk-kwuk-kwuk, uttered as a contact call by the male from the time he has started to breed; (2) a repetitive ke-ke-ke-ke… emitted by the male during copulation, the first of every three notes being stressed as coition approaches; (3) a rapidly repeated ō-ō-ō-ō … uttered by the male - yearling and adult - during high-intensity threat and often terminating in overt aggression. Ritualised billing and allopreening accompanied by various degrees of head-tilting are also described. These ceremonies probably help to reinforce the pair bond and synchronise the partners for breeding.