Abstract
Laryngeally echolocating bats avoid self-deafening (forward masking) by separating pulse and echo either in time using low duty cycle (LDC) echolocation, or in frequency using high duty cycle (HDC) echolocation. HDC echolocators are specialized to detect fluttering targets in cluttered environments. HDC echolocation is found only in the families Rhinolophidae and Hipposideridae in the Old World and in the New World mormoopid, Pteronotus parnellii. Here we report that the hipposiderid Coelops frithii, ostensibly an HDC bat, consistently uses an LDC echolocation strategy whether roosting, flying, or approaching a fluttering target rotating at 50 to 80 Hz. We recorded the echolocation calls of free-flying C. frithii in the field in various situations, including presenting bats with a mechanical fluttering target. The echolocation calls of C. frithii consisted of an initial narrowband component (0.5±0.3 ms, 90.6±2.0 kHz) followed immediately by a frequency modulated (FM) sweep (194 to 113 kHz). This species emitted echolocation calls at duty cycles averaging 7.7±2.8% (n = 87 sequences). Coelops frithii approached fluttering targets more frequently than did LDC bats (C.frithii, approach frequency = 40.4%, n = 80; Myotis spp., approach frequency = 0%, n = 13), and at the same frequency as sympatrically feeding HDC species (Hipposideros armiger, approach rate = 53.3%, n = 15; Rhinolophus monoceros, approach rate = 56.7%, n = 97). We propose that the LDC echolocation strategy used by C. frithii is derived from HDC ancestors, that this species adjusts the harmonic contents of its echolocation calls, and that it may use both the narrowband component and the FM sweep of echolocations calls to detect fluttering targets.
Highlights
Echolocating bats listen for echoes of signals to detect prey and obstacles
We have shown that the structure of the echolocation calls of C. frithii differ from those of other high duty cycle (HDC) bats, which emit calls consisting of a relatively long narrowband pulse with dominant energy and ending in a lower frequency modulated (FM) sweep
We propose that C. frithii adjusts the harmonic content of its calls and may use either the narrowband component and/or the broadband FM sweep to detect fluttering targets [4,7,15,16]
Summary
Echolocating bats listen for echoes of signals to detect prey and obstacles. While most (,700 species) laryngeally echolocating bats separate pulse and echo in time (low duty cycle – LDC), a few (,180 species) separate pulse and echo in frequency, relying on high duty cycle (HDC) echolocation. They exploit information contained in Doppler-shifted echoes to detect obstacles and locate prey [1,4]. LDC echolocators generally emit calls for less than 25% of the time that they are echolocating, and HDC echolocators for more than 25% of the time [5]
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