On PNDs 5 and 9, the isolation-induced ultrasonic vocalizations (USVs) emitted by each pup removed from the nest and placed into a Plexiglas arena were detected for 3 min by an ultrasound microphone (Avisoft Bioacoustics, Germany) sensitive to frequencies between 10 and 200 kHz [7 (link)]. The USVs were analyzed quantitatively using Avisoft Recorder software (version 5.1).
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