A dual function of echolocation : bats use echolocation calls to identify familiar and unfamiliar individuals

Abstract

Bats use echolocation for orientation during foraging and navigation. However, it has been suggested that echolocation calls may also have a communicative function, for instance between roost members. In principle, this seems possible because echolocation calls are species-specific and known to differ between sexes, and among colonies and individuals. We performed playback experiments with lesser bulldog bats, Noctilio albiventris, to which we presented calls of familiar/unfamiliar conspecifics, cohabitant/non-cohabitant heterospecifics and ultrasonic white noise as a control. Bats reacted with a complex repertoire of social behaviours and the intensity of their response differed significantly between stimulus categories. Stronger reactions were shown toward echolocation calls of unfamiliar conspecifics than toward heterospecifics and white noise. To our knowledge, this is the first time that bats were found to react to echolocation calls with a suite of social behaviours. Our data also provide first experimental evidence for acoustical differentiation by bats between familiar and unfamiliar conspecifics, and heterospecifics. Analysis of echolocation calls confirmed significant individual differences between echolocation calls. In addition, we found a trend towards group signatures in echolocation calls of N. albiventris. Consequently, we suggest that echolocation calls used during orientation may also communicate species identity, group-affiliation and individual identity. Our study highlights the communicative potential of sonar signals that have previously been categorized as cues in animal social systems.