We recorded acoustic signals during interactions between mother eastern red bats and their nursing young. Mothers and young produced tonal (structured change in frequency over time) frequency-modulated (FM) signals with varying harmonic components in situations ranging from reunion to just before nursing. Pups left by their mothers were usually silent, only occasionally producing tonal isolation calls. Adult females used FM signals in stressful situations, times when young usually produced clicks. Vibrational signals (‘hums’) composed of clicks (broadband, no structured change in frequency over time) characterized pup-pup and mother-pup interactions but pups also used other clicks that differed in frequency components from clicks comprising the hums. In stressful situations, adults produced FM signals, the pups, clicks. FM signals of pups decreased in frequencies with increasing age (size). Echolocation calls of adults and subadults hunting flying prey differed in frequency components. Differences in duration of echolocation calls coincided with setting (short calls in flight cages, open calls in the open). FM signals produced by pups searching for their mothers' nipples showed little potential for individual signatures. Calls and calling behaviour of eastern red bats that are solitary and foliage-roosting, differed from those of more gregarious species roosting in more sheltered situations.
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