Vampire bats target their social grooming to hard-to-reach body parts

Many group-living mammals and birds groom the fur (or preen the feathers) of their close associates to build and maintain affiliative relationships. Several lines of evidence suggest that social grooming in female common vampire bats (Desmodus rotundus) is a low-cost form of helping, but it has yet to be shown that vampire bats preferentially groom others in locations that are difficult to self-groom, as has been found in multiple primate species. In this short note, we show that vampire bat social grooming (n = 1586 events) occurs most often on parts of the recipient's body where self-grooming (n = 1515 events) is least likely, and often in locations where the recipient could not lick itself, like the back of the head. The finding that vampire bats preferentially groom each other in hard-to-reach locations provides further support for the hypothesis that social grooming is both a social signal and a low-cost form of helping.