Vocal behaviour during aggressive encounters between Siberian hamsters, Phodopus sungorus

Vocalizations constitute an important channel of communication for many vertebrates. Classes of vocalizations may be closely associated with particular contexts or behaviours, and variation within classes may convey information on individual identity, sex or motivational state. Rodent vocal communication has largely been studied within a reproductive context, but rodents also utter vocalizations during aggressive encounters with same-sex conspecifics. In this work we investigated same-sex vocal behaviour of Siberian hamsters, a mammalian model species for studying aggression. Males and females produced two main classes of vocalizations: high-frequency (>20 kHz), narrowband vocalizations (ultrasonic vocalizations; USVs) and lower-frequency, broadband vocalizations (broadband calls; BBCs). USVs and BBCs were further classified into subtypes based on spectrotemporal characteristics. With these classifications, we made the predictions that hamsters would utter distinct subcategories of calls, that there would be sex differences in call usage, and that BBCs would be more closely associated with aggressive behaviours than USVs. While there were no sex differences in the total number of USVs or BBCs produced by a pair, the use of vocalization subcategories varied by sex, with females uttering more variable USVs and more ‘rattle’ BBCs than males. In conjunction with these differences in vocal behaviour, the sexes also differed in aggression. Across both sexes, variation in aggressive behaviour correlated with variation in the number of ‘squeak’ BBCs and ‘rattle’ BBCs, whereas USVs were not related to aggression. Thus, BBCs constitute a distinct vocalization type with an important role in aggressive communication for hamsters.