Characteristics of Ultrasound Calls by Mouse Pups

Ventimiglia, Maria, and Ph.D. Hill

Ultrasonic Vocalizations (USVs) are whistle-like sounds, above 30 kHz, which are emitted by mouse pups.  These calls are associated with many factors, including separation from the mother, isolation from the nest, unfamiliar odors, and decreased temperature.  The calls appear to stimulate approach by the mother.  In the present study, ultrasound calls were recorded from 14 CD1 mouse pups, which had been separated from their litters and placed in a sound-attenuating plexi-glass box. A five minute recording was taken when litters were 3 (n=7) and 7 (n=7) days old.  Calls were analyzed using SPECTR III software (Binary Acoustic Technology). Types of calls were classified according to previous literature. Calls were compared between age groups using Analysis of Variance.  On average, pups emitted 320.14 (SD=185.61) calls.  The calling pattern differed by age of pups.  For 7-day olds, the number of calls decreased steadily over the 5-minute period, while for the 3-day olds, the call number was similar for each minute (Minute X Day F[4,48]=4.262, p=.005).  Pup age also influenced the types of calls emitted.  The most frequent call on either day was one with frequency steps, that is, a call that begins at one frequency, splits into two, and then returns to the original frequency.  On Day 3, the next most frequent type was one that began at a high pitch and shifted downward in pitch.  On Day 7, flat and single-harmonic types of calls were common.  Previous researchers also reported a decrease in number of calls after three minutes.  Results on call types are somewhat but not totally consistent with previous research; Branchi et al. (1998) found modulated frequency calls to be the most abundant, followed by frequency steps.  Variation in pitch within a call may assist with localization of a sound.