Vocalizations of Grasshopper Mice (Genus Onychomys)

Abstract

The sonic portion of the vocal repertoire of Onychomys (0–16 kHz) consists of two basic neonatal and four basic adult vocalization types. Two of these vocalization types, one neonatal and one adult, show major ultrasonic elements within the 20–64 kHz audio spectrum. An unusually loud and pure-tone adult call (9.5–13.5 kHz) is examined for geographic, non-geographic, and individual variation. Using six characters of the call in both univariate and multivariate analyses, we could discriminate between species, sexes, and individuals. There is, presently, no evidence for large-scale geographic patterning in call characteristics. However, closely related individuals appear to have similar, though distinguishable calls, and there is some evidence suggesting an inverse relationship between body size and call frequency (larger animals have deeper voices). The call may function as a means of maintaining inter-individual contact over long distances and, as such, contains a large amount of information of potential use to other grasshopper mice including: 1) direction of the caller; 2) distance; 3) species of the caller; 4) caller's sex; 5) age (whether adult or juvenile); 6) caller's size. This vocalization has a high potential for use in remote censusing of natural Onychomys populations, and will, in addition, function as a natural marker for the monitoring of individual grasshopper mice in future field studies.