Biological basis of grooming behaviour in antelope: the body-size, vigilance and habitat principles

Abstract

Grooming in ungulates has been shown to be very effective in removing ectoparasites. Ectoparasites, especially ticks, may be costly to an animal's resources in terms of blood removed and depression of appetite. There are two opposing models that address the parasite-control of function of grooming: (1) animals may groom in response to stimulation from parasite bites, whereupon those with the most parasites should groom the most; or (2) animals may groom prophylactically, removing parasites such as ticks before they attach, as a reflection of a central programming or timing mechanism. Based on behavioural observations of Thomson's gazelle, Gazella thomsonii, Grant's gazelle, Gazella granti, impala, Aepyceros melampus, and wildebeest, Cannocheates gnu, in Kenya and at the San Diego Wild Animal Park (SDWAP), both models seemed to apply to different aspects of grooming. Presumably, as a reflection of their increased vulnerability to ectoparasites through a greater body surface to mass ratio (body-size principle), Thomson's gazelle were found to groom more frequently than wildebeest. This corresponds to a reportedly smaller number of ticks per m 2 surface area in Thomson's gazelle. Territorial males groomed less frequently than conspecific females and bachelor males, presumably relfecting their need to remain vigilant over females (vigilance principle). Within-species grooming was less in a low-parasite environment (SDWAP) than in a high-parasite environment (Kenya), reflecting both a decreased exposure to parasites (habitat principle) and a decrease in programmed grooming. Impala, which typically inhabit tick-infested woodland areas, orally groomed themselves more than the size-matched Grant's gazelle comparison species, and also engaged in a unique form of reciprocal allogrooming of the head and neck. That the impala allogrooming may also have a tick-removal function was supported by the finding that impala scratch-groom the head and neck less than Grant's gazelle.