Differential grooming rate and tick load of territorial male and female impala, Aepyceros melampus

Abstract

During the breeding season in Zimbabwe territorial male impala were found to engage in much less self oral grooming and allogrooming than females, presumably as a reflection of the need to remain vigilant in herding females and repulsing challenging bachelor males. Territorial males spent an average of 11 min engaged in all types of grooming during a 12-h day, compared with 40 min grooming by females. Rutting activity and time spent scanning peaked in May, while self oral grooming and feeding by territorial males was lowest at this time. The decrement in grooming by males (relative to females) represented half of all time devoted to rutting behaviors. Territorial males appeared to sacrifice feeding and grooming time in exchange for more time devoted to vigilant activities essential to mating success. In a comparable region of Zimbabwe, territorial males were also found to harbor about six times as many adult ticks as the females on the same territories during the breeding season. Because grooming is understood to be effective in removing ticks, the higher tick load of territorial males was attributed to their reduced grooming behavior. However, testosterone and adrenal cortical steroids, which are elevated in territorial male impala, are known to depress the immune system, and so may be important in controlling parasite infections. Sexually active males of many species are generally found to harbor more parasites than females. The difference in tick load between territorial male and female impala may reflect both behavioral and hormonal parameters.