The social organization of the common vampire bat

Summary At a site in Costa Rica, three groups of 8–12 adult female vampire bats, Desmodus rotundus, utilize group-specific sets of hollow trees as day roosts. Long-term nonrandom associations between pairs of females, as measured by the proportion of time one bat spends roosting in the same tree with another bat over a 3 year period, occur even when preferences for particular trees are removed. Significant associations exist between both related and unrelated adult females. Adult male bats, however, show few associations with females or other males. By observing bats within trees and while foraging, and by monitoring feeding flights with radiotelemetry, the following potential benefits of association could be tested. Females roost together to (1) share a suitable microclimate, (2) avoid predators, (3) avoid ectoparasite infestations, (4) minimize travel to mobile prey animals, (5) respond to coercive males, (6) feed simultaneously from a bite, (7) remove ectoparasites by allogrooming, and (8) share food by regurgitating blood to other bats within roosts. The data do not indicate that any of the first five hypotheses provide significant benefits for long-term associations although predators and ectoparasite levels may cause occasional changes in roost sites. Simultaneous feeding was uncommon and apparently confined to females and their recent offspring. Allogrooming, although common, occurred independently of the presence of ectoparasites. Food sharing, however, occurred between both related and unrelated adult females with high levels of association and provides at least one selective advantage for maintaining cohesive female groups.