ANALYSIS OF 22 KHZ ULTRASONIC VOCALIZATION IN LABORATORY RATS - LONG AND SHORT CALLS

There is a remarkable variation in the length of single ultrasonic cal ls emitted by adult rats. The duration of calls is likely to convey in formation for conspecifics. The goal of the present study was to analy ze 22 kHz calls emitted by naive laboratory rats in response to contac t with the human hand and to measure their acoustic features, with a p articular emphasis on call duration. Repeated hand touch applied to th e nape of the neck of rats induced ultrasonic calls, 97.4% of which we re within the range of 20-29 kHz and 2.6% of which were within 44-67 k Hz. Distribution of duration of 6765 calls revealed two subpopulations of 22 kHz calls: 20-300 ms calls with its peak at 150 ms and calls ab ove 310 ms with highest values at approximately 500-600 ms without a c lear peak. These two call populations were referred to as short and lo ng calls, respectively. The short and the long vocalizations contained 80% and 100% of calls within the range of the 22 kHz frequency, respe ctively. The findings indicated that, in the situation studied, the 22 kHz vocalization of adult rats consists of two distinguishable subpop ulation of calls: short and long with the boundary between them at 300 ms.