Relation between 22-kHz ultrasonic signals and sociosexual behavior in rats

The copulatory performance of male rats, tested in a large seminaturalistic environment, was assessed to determine the relation between 22-kHz ultrasonic vocalizations and a range of sociosexual behaviors. The male rats were tested until sexual exhaustion. Such ultrasonic signals were shown to occur in a wider range of sociosexual circumstances than previously reported; for example, the calls occcurred in particular social circumstances during the preejaculatory period as well as during the postejaculatory interval. There was no consistent evidence that the emission of this call during the postejaculatory period consistently functions to keep the female away from the male. The nature and occurrence of postejaculatory ultrasonic signals showed increasing variability in successive ejaculatory series. The results of this and previous studies are interpreted within a semiotic theory of communication. The 22-kHz call is described as a message that makes available the information that the sender is in a socially depressed and withdrawn state.