We analyzed the ultrasonic calls of adult black rats, Rattus rattus, with acoustic analysis software, Adobe Audition 2.0. The rats intermittently produced 1 to 7 ultrasound waves in a series of calls. The waves showed a higher frequency and longer duration at the start of the calls than in the subsequent waves. The mean frequencies of the calls at the start, 28.9̮3.0 kHz, were significantly higher than at the end, 27.5̮2.3 kHz ( p̮0.0001). The mean frequencies in females, 28.5̮ 1.5 kHz, were significantly higher than in males, 26.3 ̮ 1.4 kHz ( p̮ 0.0001). The mean duration of the ultrasound calls in females, 920̮612 ms, was longer than in males, 700̮416 ms. There was a significant di#erence between males and females in the duration of the calls ( p̮0.01).
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