Echolocation in the notch-eared bat,Myotis emarginatus

Summary In Myotis emarginatus, the patterns of echolocation sounds vary with different foraging habitats: In commuting flights the echolocation sounds are linearly frequency modulated sweeps that start at about 100 kHz, terminate at 40 kHz, and have a duration of 1–3 ms. They consist of a loud first harmonic. The second and third harmonics are at least 15 dB fainter than the first one and often undetectable. A distinctly different type of sound is emitted when the bats search for flying insects in open spaces. The sounds are reduced in bandwidth and elongated by a constant frequency component that follows the initial frequency modulated part. Typically, sounds start at about 94 kHz and terminate in a constant frequency component at about 40–45 kHz. The average duration of the constant frequency tail is 2.8 ms; this approximately doubles the length of the pulse, with the longest recorded sound lasting 7.2 ms. When bats are foraging near and within foliage, and gleaning prey from foliage, echolocation sounds are brief (average 1 ms) frequency modulated pulses with a broad bandwidth. The pulses start at about 105 kHz and sweep down to 25 kHz. During gleaning within a building, the frequency range of the sounds is shifted to higher frequencies and extends from 124 to 52 kHz. When the bats forage for aireal insects in a confined area that creates echo-clutter, they emit sounds similar to those used during gleaning within buildings except that sound durations are extended to about 1.8 ms. In each foraging area, the echolocation sounds emitted during the search for and approach to prey are similar in structure. Sound and pause durations are reduced in the approach phase. Irrespective of foraging style and habitat, immediately before capture the bat emits a rapid and stereotyped sequence of 2-10 echolocation pulses (final buzz). These pulses are brief (0.2–0.5 ms), frequency modulated sounds with a reduced bandwidth. The sounds start at 45 kHz and sweep down to 35–20 kHz. The repetition rate is increased up to 200 pulses/s. Offprint requests to: G. Neuweiler