Fig. 1. Spectrograms of sonar sounds emitted by a big brown bat in target-detection tasks while wideband random noise of different amplitudes was delivered from a loudspeaker (Simmons et al., 1974). In response to the noise, the bat lengthens its FM sweeps, which have a curvilinear shape and tail down to a shallow sweep around 22–28 kHz (arrow). Its detection performance remains approximately constant in ambient conditions and in –40 to –10 dB noise, but it declines to chance in 0 dB noise.