Evolution and Function of Drumming as Communication in Mammals
An amazing variety of mammals produce seismic vibrations by drumming a part of their body on a substrate. The drumming can communicate multiple messages to conspecifics about territorial ownership, competitive superiority, submission, readiness to mate, or presence of predators. Drumming also functions in interspecific communication when prey animals drum to communicate to predators that they are too alert for a successful ambush. The diversity of mammals that drum in varied contexts suggest independent evolution in different lineages. Footdrumming, as with other signals, probably originated by ritualization of older forms of behavior not associated with communication such as running and digging. Footdrumming patterns are species specific and range from single thumps to individual footdrum signatures. Although mammals communicate above ground with airborne drumming signals, they can also transmit sound seismically into the burrow where the signals become airborne and are received with ears especially adapted to hear low-frequency sound. Footdrumming has been studied the most extensively in kangaroo rats, Dipodomys. A comparison of species of different body mass shows that smaller sized, non-territorial species have no ritualized footdrumming; medium-sized species drum a simple pattern in limited contexts; while larger-sized species communicate territorial ownership with complex patterns. Future studies should examine the mechanics and energy requirements of drumming to test hypotheses about body size limitations on the evolution of footdrumming. Our understanding of drumming as communication is limited until investigators conduct field tests of responses to drumming signals in the contexts in which the signals are generated.