An investigation of the pulses produced by the least shrews (Cryptotis parva)

Abstract

Most echolocation studies have focused on bats and dolphins. Because of technological improvements in ultrasonic sensing and recording equipment, there now are cost-effective approaches towards examining ‘‘other’’ groups of mammals for possible echolocation abilities. In this study, we suggest that echolocation is a primitive characteristic, first appearing in insectivores, the ancestor of all other placental mammals. A few other studies and anatomical, behavioral, and physiological attributes suggest that shrews are likely to echolocate. In captivity, least shrews (Cryptotis parva) produce series of pulses. We used a board divided into an inner and outer box of equal area to run 8 least shrews through a set of foraging and orientation experiments. Experiments were in the dark and we monitored the circumstances under which shrews produced pulses using a night-vision video camera. An ANABATII bat detector monitored the presence of pulses, a Marantz cassette recorder documented the sounds, and Audioscope software on a laptop computer provided real time sonogram and oscillogram displays. The number of pulses and trains, the typical waveform, power spectrum, peak frequency, and bandwidth (−3 dB) were examined among the experiments. Results provided strong evidence that least shrews use simple pulses for both orientation and foraging.