Echolocation by free-tailed bats (Tadarida)

Summary The echolocation of bats in the genusTadarida is highly adaptive to different acoustic conditions. These bats use different types of sonar signals with a diversity usually observed in comparisons across families of bats.Tadarida brasiliensis andT. macrotis search for airborne prey in open, uncluttered spaces using narrow-band, short CF signals with no FM components. They add broadband FM components while dropping the CF components when approaching or capturing prey. Only one harmonic is present in these insect-pursuit signals. When flying in cluttered situations or echolocating in a laboratory room,T. brasiliensis uses multiple-harmonic FM signals. Stationary bats tend to use linear frequency sweeps and moving bats tend to use curvilinear frequency sweeps or linear period sweeps. When emerging from a roost they initially use a short-CF/FM signal, changing to an FM signal as they fly away. The acuity of perception of target range inT. brasiliensis is about 1.0 to 1.5 cm and is determined by the bandwidth of the target-ranging sonar signals as represented by their autocorrelation functions. Many less adaptable species of bats use signals corresponding to part of the sonar repertoire ofTadarida. The functions of short CF or narrowband signals for detection and FM or broadband signals for resolution and acoustic imaging identified from comparisons among such species are confirmed by observations of echolocation byTadarida. The differences observed in echolocation among many species and families of bats appear to be evolutionary adaptations to some of the same features of the acoustic environment to whichTadarida responds behaviorally.Abbreviations CF frequency modulated - FM constant frequency - LPM linear period modulation - LFM linear-frequency modulation We thank Prof. T.T. Sandel, Prof. D.R. Griffin, Dr. George Pollak, and P.H. Dolkart for their advice and assistance. This research was supported by Grant No. BMS 72-02351-A01 from the National Science Foundation and by Biomedical Research Support Grant No. RR-07054 from the Division of Research Resources, National Institutes of Health.