Plasticity in the echolocation inventory of Mormopterus minutus (Chiroptera, Molossidae)

We recorded the echolocation behavior of the molossid bat Mormopterus minute's, a species that uses a plastic call inventory. During its foraging activity, M. minutus searches for insects emitting rather long and narrow-band echolocation calls. Search call design however, can vary noticeably even in a continuous foraging pass. While echolocating in different flying conditions M. minutus uses several other call designs such as short CF, QCF, FM/QCF, FM and multi-harmonic FM, with or without harmonic overlap, and QCF/FM. Call plasticity characterizes most echolocation sequences, particularly in bats flying in open spaces. Call variation was also influenced by the presence of conspecifics. In those sequences containing echolocation calls from more than one bat, signals from different individuals were reliably identified. In contrast to other small molossids, the call designs in the echolocation inventory of M. minutus show a high level of plasticity. Our results suggest that M. minutus has combined the advantages of emitting several call designs, as shown by molossids, with the advantages of manipulating one signal design as shown by vespertilionids within the same sonar inventory.