Data from: Do vampire bats groom others based on need?

Allogrooming provides a window into the social lives of many group-living
mammals and birds. The fitness benefits of allogrooming are encouraged by
proximate mechanisms that make it physiologically rewarding for both
actors and receivers. However, receivers might not always benefit from
allogrooming. Some allogrooming decisions might be the actor’s response to
cues of the recipient’s need. Other decisions might only be caused by the
actor’s motivational state. To test these ideas, we studied what triggers
allogrooming in common vampire bats. In test 1, subjects that had
experimentally disturbed and wetted fur were more likely to be
allogroomed, even when controlling for increased self-grooming. In test 2,
allogrooming rates were elevated by receiver self-grooming (a cue for
receiver need) but also by the actor’s previous self-grooming. Both
effects were significantly greater than the effect of self-grooming by
third-parties. Interestingly, we detected a negative interaction: the
positive effect of receiver need on allogrooming was smaller when the
actor was previously self-grooming. This is consistent with the hypothesis
that there are ‘receiver-driven’ allogrooming decisions, which are
responses to recipient need, and ‘actor-driven’ decisions, which are not.
We predict that receiver-driven allogrooming will bestow greater benefits
to recipients compared to actor-driven allogrooming.