When mother-offspring couples of Phyllostomus discolor (lesser spear-nosed bat) are reunited after separation, an intensive exchange of infants' isolation calls and mothers' directive calls can be observed. The directive calls of each mother show a distinctive frequency-time structure, which appears to represent her individual vocal signature. During ontogenesis the isolation calls of the young change gradually, adapting increasingly to the mother's call type. A comparison of calls of separated pups at different ages with their mothers' directives demonstrated the individually distinct call characteristics of the mother also to be characteristic of the isolation calls of her young by about 50 days of age. This suggests that acoustic signals may be learned in Phyllostomus discolor.