EN
Females of several species of rodents are known to emit audible and ultrasonic sounds during same-sex encounters. There is very little information about factors affecting this vocalization. The present study was undertaken to investigate the effect of the stage of the reproductive cycle on vocalization and behaviour of adult bank vole females during various same-sex encounters. Pregnancy and lactation were studied as important phases of female life. The possible role of ovarian hormones in the emission of acoustic signals was also investigated as these hormones are known to be important in the regulation of other female social behaviour. The behaviour and vocalization of sexually naive, ovariectomized, pregnant and lactating females were studied using 10-min confrontation tests. The results demonstrate that the behaviour displayed and the emission of sounds in female–female bank vole encounters depend on the phase of reproductive cycle. Ultrasounds are produced more often by sexually naive and ovariectomized females which present mainly non-aggressive behaviour than by more aggressive lactating females. Audible sounds are emitted only occasionally by naive and by ovariectomized females but pregnant and especially lactating females emitted such calls more often, with shorter latencies and for longer than the unmated groups. Ultrasonic vocalization therefore seems to be related to non-aggressive behaviour and audible vocalization to aggression.