Social grooming in the common vampire bat, Desmodus rotundus

Grooming patterns among 65 common vampire bats in hollow tree day roosts were studied by behavioural sampling techniques during a 15-month period. Self-grooming occurred more than social grooming in response to ectoparasites since the proportion of time spent self-grooming and the amount of ectoparasite infestation covaried positively among tree roosts, while the time spent grooming others was independent of roost and ectoparasite level. Rates of social grooming were not independent of the sex of participants due to infrequent social grooming by adult males. Two variables, the level of relatedness and a measure of roosting association, which previously were shown to predict food sharing by regurgitation, correlated positively with the rate of social grooming. Since social grooming occurred more often than expected before a regurgitation and correlated with regurgitation frequency, it is suggested that this behaviour facilitates identification of food sharing partners by enabling a grooming bat to monitor other animals' potential for giving or receiving blood. The functional significance of social grooming (licking, nibbling or picking at the fur ofa conspeci- tic) has yet to be unequivocally demonstrated in any species. If one assumes that social grooming costs a donor time that could have been allocated to self-maintenance or feeding but benefits a reci- pient either by removing ectoparasites (Freeland 1976), by helping to heal wounds (Simonds 1965), or by increasing the likelihood of support in an aggressive dispute (Seyfarth 1977, 1980, 1983; de Waal 1982), then either kin selection (Kurland 1977; Silk 1982) or reciprocity (Seyfarth & Cheney 1984) must be invoked to explain the occurrence of this behaviour. However, Dunbar & Sharman (1984) reviewed 40 baboon studies which measured the amount of time spent feeding, resting and social grooming and failed to find the expected negative relationship between time spent feeding and time spent social grooming. Instead, they discovered that the time allotted to ~social grooming was conserved. During periods of food shortage, rest- ing time decreased to permit extended feeding periods. Consequently, at present there is no evidence that social grooming costs a donor by decreasing its reproductive success or survival. Furthermore, although some primates groom conspecifics in locations that are hard to reach (Hutchins & Barash 1976) and around recent wounds (Simonds 1965), there is little evidence to demonstrate that social grooming directly benefits a recipient by enhancing its survival or reproduc-