FARRAR, D.M.; MONROY, J.A.*; CARTER, M.E.; COVEY, E.; CASSEDAY, J. H.; University of Washington, Seattle: Mother-infant communication in the big brown bat, Eptesicus fuscus

The first vocalizations emitted by infant big brown bats develop into several types of calls. Many of these calls serve to communicate with their mothers. Big brown bats form large maternity colonies consisting of as many as 100 females and their pups. If the pups are separated from their mothers, they can locate each other using vocalizations. The goal of our study was to characterize the spectrotemporal structure of calls used in mother-pup interactions and to determine how these calls are used when the two become separated. Six bat pups from three pregnant females were isolated from our captive colony at the Univ. of Washington. We recorded and analyzed the structure and distribution of call types from postnatal day 1 to day 35. Calls emitted by isolated pups were compared to calls emitted when the mother was introduced. Isolated pups emitted calls that developed into rapid downward FM sweeps similar to adult echolocation calls. As the young bats matured, the maximum and minimum frequencies of these calls increased as the duration decreased. Calls recorded from pups when the mother was introduced resembled adult communication calls and mother-pup communication calls of other species. Such calls were characterized by a downward FM sweep followed by a tail that varied in structure. In general, these calls spanned lower frequencies and had longer durations than calls that were emitted when a pup was alone. During mother-infant interactions, the mother also emitted calls in response to her pup�s calls. It is possible that these function as directive calls that facilitate acoustic learning in the pup. Our data suggest that vocalizations play an important role in mother-infant communication and that big brown bats may use vocal signatures in these calls to find each other in large groups.