Ultrasounds during agonistic interactions between female rats (Rattus norvegicus)

Defensive and vocal behaviors of 18 female Long-Evans rats (Rattus norvegicus) in encounters with aggressive, lactating conspecifics were examined in order to determine if female rats emit ultrasounds during agonistic interactions and to characterize any such calls. The subjects, selected during estrus or diestrus, were exposed to 1-min attacks at 25-min intervals. Between attacks the subjects were threatened by the aggressor but protected by a wire-mesh cage. Female rats emitted both high- (32-60 kHz) and low-frequency (20-32 kHz) ultrasonic calls in agonistic encounters, with the rate of high-frequency calls enhanced during estrus. Low-frequency ultrasounds were shorter in duration and higher in frequency than those emitted by male rats in similar conditions. We conclude that female rats emit ultrasonic calls during defensive responding and that the characteristics and rate of calling vary as functions of sex and gonadal hormone state.