In the lesser spear-nosed bat (Phyllostomus discolor) pups progressively adapt the structure of their isolation calls by audio-vocal learning to the individually distinct frequency modulation pattern of the maternal directive call. Directive and isolation calls are frequently used during acoustic mother-infant interactions, and both are sinusoidally frequency-modulated signals. The ability of audio-vocal learning is commonly accepted as a prerequisite for language acquisition in humans and for song plasticity in a variety of avian species. As a consequence of vocal plasticity traditions may arise and lead to local dialects in humans and birds. To test whether a similar formation of dialects occurs in P. discolor we analyzed the directive calls of two laboratory breeding colonies of these bats with regard to three call characteristics contributing to a mother's "vocal signature" (i.e., the number of frequency minima and maxima per call, the carrier frequency, and the modulation frequency). The geographical origin of one colony is Costa Rica and the other Columbia. As revealed by statistical comparison of group means of the above sound parameters and as further shown by multidimensional scaling techniques, female dialects clearly exist in P. discolor.
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