Thesis

Sound communication in the California ground squirrel

The purpose of this study was to examine the vocal communication system of the California ground squirrel, Spermophilus beecheyi. Tape recordings of the sounds of marked squirrels were made in the field, while concurrent notes were taken on the behavior of the animals; feeding boxes were used for intensifying interactions among individuals. Supplementary data were collected from captive squirrels. The recordings were analyzed with a sonagraph. On the basis of their physical properties, vocalizations fell into six distinct groups: chatters, squeals, grunts, whistles, screams and tooth chatter. By combination and repetition of these sounds, the use of the same sounds in different contexts, and the use of graded signals, the number of messages used for communication was increased. Two types of alarm calls were given in response to predators: squeal indicated an immediate alarm; a long call (chatters followed by repeated signals) served as an alerting signal for less immediate danger. Females were found to be more alert than males and gave most of the long alarm calls. A whistle was emitted during sexual chases. During agonistic encounters, grunts and chatters were used in association with dominance and a tendency to attack, while a squeal was used to indicate subordination and a tendency to flee. Some sounds (grunts, screams and tooth chatter) were found to be associated with territorial defense.

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