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We investigated the vocalizations produced by adult pine voles during various social interactions by presenting an experimental animal with either an anesthetized or awake (unanesthetized) conspecific. Ultrasonic vocalizations (USVs) occurred frequently during tests in which an awake male was present, but were rarely detected in tests involving only awake females, or when a female was presented with an anesthetized conspecific. Higher rates of USVs were produced when males were tested with a familiar female than when tested with an unfamiliar male or female. Equivalent rates were produced when males were presented with either anesthetized or awake animals, but female-soiled bedding failed to elicit USVs from males. Sonic vocalizations (SVs) were produced by both sexes and were associated with aggressive behavior, but occurred only in tests between awake, unfamiliar animals. Castration greatly reduced and testosterone therapy restored USVs emitted by males in response to anesthetized conspecifics. Our results suggest that (i) USVs are emitted predominantly by males; (ii) familiarity enhances USV response; (iii) SVs are produced during aggressive interactions; and (iv) androgens regulate the production of USVs by males. Possible roles for pine vole vocalizations are discussed.

Male and female Microtus ochrogaster were presented with anesthetized and awake conspecifics while ultrasonic vocalizations (USVs) were monitored. Males produced significantly more USVs than females during 5-min testing sessions. Males tended to produce more USVs to unfamiliar females than to familiar female siblings. Sexual experience led to increased USV scores by males. These results suggest that USVs by male prairie voles communicate to females the male's gender and his availability for reproductive behavior.