Analysis of ultrasonic vocalizations emitted by residents during aggressive encounters among rats (Rattus norvegicus).

Determined the extent to which aggressive resident rats emit 40–70-kHz vocalizations and the effect of these signals on intruders. In Exp I, 16 deafened and intact intruder male Long-Evans rats were given 2 encounters with 8 resident Ss. Deafened intruders engaged in a higher duration of immobile or freezing postures than intact Ss. Exp II indicated that the augmentation of freezing found among deafened intruders was not due to an inability to detect ultrasounds made by residents since intruders encountering devocalized resident males showed no reliable differences in specific motor patterns from intruders paired with intact residents. Results demonstrate that 40–70-kHz vocalizations were produced almost entirely by intruding Ss since there were no significant changes in occurrence of these calls when resident males were devocalized. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)