Infantile stimulation and ultrasonic signaling: A possible mediator of early handling phenomena

Abstract

Peromyscus maniculatus bairdi were either handled or not handled daily during the first 10 days of life. Handling consisted of removing the infant mice from the litter, placing them in small individual compartments where they remained for 3 min, and then replacing them in the nest. Immediately following the handling, simultaneous video and audio recordings were made of nest behavior for two 30‐sec recording sessions. The nonhandled controls were treated comparably except that pups were never removed from the nest. Handled litters differed from nonhandled in terms of the average number of signals per recording session (132.5 vs. 16.5), the average signal duration (0.108 sec vs. 0.045 sec), and the average peak frequency of signals (22.216 kHz vs. 11.990 kHz). During those recording sessions in which no vocalizations were detected no physical interaction appeared between the mother and the infants. During all sessions in which vocalizations were emitted the mother was retrieving and grooming the infants. The data suggest a possible interpretation of the effects of early handling in terms of modified mothering, medidiated by modified vocalizations of infant mice as a function of the handling.