What's in a squeak? Female vocal signals predict the sexual behaviour of male house mice during courtship

Vocal production can be a two-way channel for the exchange of information between males and females during courtship. Although the ultrasonic vocalizations (USVs) of male house mice, Mus musculus, during interactions with females have been a focus of communication research, the vocalizations of females in this context remain poorly understood. During interactions with males, female mice produce audible vocalizations with a broadband harmonic structure ('broadband vocalizations', or BBVs) that are often described by human listeners as 'squeaks'. We tested the hypothesis that the production of BBVs corresponds to male and female behaviours, as well as to contextual variables like oestrous phase, by measuring BBVs, USVs and nonvocal behaviours during 39 unique male-female pairings. We found that the relationship of BBVs to other behaviours depends on the phase of courtship. A high incidence of BBVs accompanied by male-directed kicks and lunges early in interactions predicted a lack of later male mounting and male-produced '50 kHz harmonic' USVs. In contrast, there was significant temporal overlap between BBVs and 50 kHz harmonic USVs at later stages of courtship, potentially driven by mounting events. The duration of acoustically nonlinear segments of BBVs varied significantly among females, even across interactions with different males, but also varied across oestrous phase within females. These findings suggest that vocalizations could play a role in signalling acute female motivational state, identity or oestrous state during opposite-sex interactions. Since the information-bearing features of BBVs are relatively easily measured, they are potentially a useful readout of negative motivational state suitable for many research and educational applications.