Ultrasonic bouts of a blind climbing rodent (<i>Typhlomys chapensis</i>): acoustic analysis

The peculiar acoustic structure of ultrasonic bouts of blind climbing rodents <i>Typhlomys</i> might provide insight on their potential function. We examined 1481 bouts consisting of 1-6 pulses; 49.7% of them were single-pulse bouts. Bout duration and inter-bout interval depended on the number of pulses per bout, whereas period from start of a previous bout to start of the next bout was constant (80.0±2.9 ms). Ultrasonic pulses (540 pulses measured in a subset of 234 bouts) were short (0.68±0.15 ms) sweeps with fundamental frequency slopes from 127.3±6.3 kHz to 64.1±4.6 kHz and peak frequency at 93.3±7.4 kHz, emitted within bouts with inter-pulse periods of 13.03±3.01 ms. Single pulses and start pulses of multi-pulse bouts were lower in frequency than other pulses of the bouts. In contrast, pulse duration was independent on pulse position within bout. Pulses of <i>Typhlomys</i> were reminiscent of echolocation calls of <i>Murina</i> and <i>Myotis</i> bats, but higher in frequency, much shorter, fainter, displayed a convex contour of frequency modulation and only the fundamental frequency band without harmonics and were organized in bouts, that is not characteristic for bat echolocation. Most probably, <i>Typhlomys</i> uses their ultrasonic pulses for call-based orientation during locomotion, including climbing and jumping among bush branches.