Rodent ultrasonic short calls: locomotion, biomechanics, and communication.

Rodents of many species emit short ultrasonic vocalizations during copulation, aggression, and other activities. Thiessen and Kittrell (1979) hypothesized that ultrasound emission by gerbils is the acoustic by-product of physical compression of the thorax during certain locomotor behaviors. I carry this hypothesis further by relating gerbil ultrasound to the biomechanics of respiration during locomotion. I also suggest that at least some of the ultrasonic emissions of other rodent species are, like the gerbil's, by-products of thoracic compression during locomotion. Support for this suggestion comes from descriptions in the literature of ultrasound emission as well as slow-motion analysis of rat copulatory behavior. Finally, this alternative view of rodent ultrasound has consequences for the interpretation of experimental findings in ultrasound research and for the understanding of messages and meanings in rodent communication.