Mother-Infant Communication in a Horseshoe Bat (Rhinolophus ferrumequinum nippon): Vocal Communication in Three-Week-Old Infants

The vocal communication of Japanese greater horseshoe bats was analyzed by experimental separation of mothers and young. When separated from their mothers, infants first emitted broad-band “attractive calls” and the mother responded by emitting “lead signals.” During this process of mutual signalling, the acoustic character of the infants’ sounds and the mutual patterning of signal emission gradually and repeatedly changed. Finally, the high-pitched signals of mother and infant precisely overlapped until the pair was reunited. The vocal signals involved in mother-young communication were divided into two categories: 1) highly communicative signals such as “attractive calls,” “recognition calls,” and “contact calls”; and 2) basically echolocative but functionally communicative signals such as “lead signals” and “high-pitched signals.” It was not the physical structure of the signals, but their mutual patterning that seemed to be important in mother-infant communication. Analysis of these mutual signalling processes showed that either the mother or the infant or both coordinated their signals both temporally and phasically. In the final high-pitched stage, the mother emitted signals at a constant pitch while the infant changed pitch until attaining precise synchronization with the calls of the mother. The high-pitched synchronization with frequency coincidence of signals seemed to be essential for mother-infant communication.