Ultrasonic calling during fear conditioning in the rat: no evidence for an audience effect

Rats, Rattus norvegicus, produce 22 kHz ultrasonic vocalizations in aversive situations such as during exposure to cats or fear conditioning. These calls are considered to be part of the animal's defensive repertoire and might serve as alarm signals for conspecifics. The aim of the present study was to test whether the production of 22 kHz calls is affected by the social context during fear conditioning. Animals were tested in one of three experimental conditions: either alone, with an anaesthetized conspecific, or with an active conspecific. In line with the hypothesized alarming function of 22 kHz calls, we expected the presence of a conspecific to potentiate the production of 22 kHz calls. The results, however, show that the production of 22 kHz calls during fear conditioning is clearly not potentiated by the presence of a conspecific; if at all, its presence had a mild attenuating effect on call rate. Also, call characteristics were similar in all three experimental conditions. Therefore, our findings do not support the hypothesis that the sender actively produces 22 kHz calls to warn conspecifics about danger.