You can learn a lot about the social life of an animal by learning what forms of communication they use. The communication system of vampire bats is similar to some other highly cognitive and cooperative species, like bottle-nosed dolphins. Both vampires and dolphins produce biosonar clicks and use longer tonal sounds that sweep through a range of frequencies to maintain contact with each other. When dolphins are isolated from groupmates, they produce contact calls that convey their individual identity. I had previously shown that adult white-winged vampire bats also produce similar contact calls that convey individual identity that elicit vocal responses from other bats. These calls allow bats to discriminate each other at a distance in the darkness. We demonstrated this through playback experiments, like the ones below.
The contact calls also allow bats to find and locate each other. We know this because of the following experiment. First, we put 4 caged white-winged vampire bats in the corner of a dark room. The bats called to each other and responded to each other. In test trials, we moved the bats randomly such that everyone was in a new corner and recorded the calls and responses. In control trials, we moved the bats the same amount but everyone ended up in the same corner. As we expected, the bats called more often and a higher percentage of their calls were answered during test trials (when the bats were disoriented with respect to each others’ locations). In other words, bats used these calls more when their groupmates were in unknown locations; it was as if the bats called and responded until they all knew where everyone was located.
However, we had never seen this same call and response behavior in the other two species of vampire bats. In most bat species, it is only the mothers and pups that exchange social calls in this manner. There are exceptions. For instance, disc-winged bats also exchange contact calls to find each other. Greater spear-nosed bats produce contact calls called screech calls, but they don’t exchange them and the calls convey group membership not individual identity. So are contact call exchanges specific to white-winged vampire bats? or do the other vampire bats use them as well?
I just recently published a paper on social calls of vampire bats which compares the social call structure of the three vampire bat species. It turns out that, although only white-winged vampire bats appear to match each others calls in time, all three species do indeed use contact calls that are structurally specific to each individual. We found that the calls also vary between colony and population. Our results were at least consistent with the possibility that vampire bats, like greater spear-nosed bats, produce calls that acoustically converge within groups, while still maintaining individual signatures. However, more study is needed to test this idea. There is much more to the paper, but you can read it yourself here because it’s made freely available by the non-profit Public Library of Science