Ultrasonic bouts of a blind climbing rodent (Typhlomys chapensis): acoustic analysis

The peculiar acoustic structure of ultrasonic bouts of blind climbing rodents Typhlomys 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 Typhlomys were reminiscent of echolocation calls of Murina and Myotis 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, Typhlomys uses their ultrasonic pulses for call-based orientation during locomotion, including climbing and jumping among bush branches.