Small Mammals Ignore Common Rules: A Comparison of Vocal Repertoires and the Acoustics between Pup and Adult Piebald Shrews Diplomesodon pulchellum

A common rule for mammals vocalizing in the human audible frequency range (20Hz-20kHz) suggests that calls are higher in fundamental frequency (f0) in the young than in adults, because of the smaller sound-producing structures of the young. Exclusions are rare, for example the pups of Asian house shrews (Suncus murinus) make some call types of the same or higher pitch than adults. In this study, calls from 62 piebald shrews (Diplomesodon pulchellum), 37 1 to 10-d-old pups from 10 litters and 25 adults were acoustically investigated in captivity. We found eight call types, all within the human audible frequency range: short and long low-frequency squeaks with nearly flat contour, high-frequency squeaks with modulated contour, high-frequency squeaks with fractured contour, short and long screeches, clicks and whimpers. Seven call types were shared by pups and adults, suggesting that this vocal repertoire commences at birth. Against the common rule, the f0 of squeaks was the same in pups and adults, and the f0 of clicks and screeches was even higher in adults than in pups. These results suggest a non-descending ontogenetic pathway that not follows the common physical relationship, of the lower f0 for the larger vocal folds.