Nonmutual vocal mother–pup recognition in the greater sac-winged bat

Abstract

We investigated the acoustical component of the recognition process leading to successful mother–pup reunions in the greater sac-winged bat, Saccopteryx bilineata, using both a statistical approach and playback experiments. Statistical evidence for individual distinctiveness was found in the isolation calls uttered by pups and, to a weaker degree, in the echolocation pulse trains emitted by mothers. In contrast to other bat species, isolation calls of S. bilineata pups were complex and multisyllabic, with most of the vocal signature information encoded in the composite syllables at the end of calls. Playback experiments with free-living bats revealed that mothers were able to discriminate between their own pup and an alien young on the basis of isolation calls alone, which confirms the results of the acoustical analysis on vocal signatures in isolation calls. Pups, on the other hand, indiscriminately vocalized in response to echolocation pulse trains from their own and alien mothers, rendering the mother–pup recognition process unidirectional. The one-sidedness of the vocal recognition process in S. bilineata as well as in other bat species might be explained by a lack of selection pressures that shape mutual vocal parent–offspring recognition in other species of mammals and birds. To our knowledge, this study is the first in which playbacks were used to elicit antiphonal calling behaviour between bat mothers and pups experimentally. We argue that vocal responses to playback stimuli are a more feasible and reliable response measure for conducting mother–pup recognition playbacks in bats than the phonotaxis behaviour used in the past.