Vocal communication and the development of hearing in the pallid bat, Antrozous pallidus

Abstract

Adult pallid bats (Antrozous pallidus) communicate via four main types of sound emissions: directives, squabble notes, irritation buzzes, and orientation pulses. The isolation call is the only sound emitted by newborn bats. It changes in quality as the bat matures, until by the twentieth day it resembles the adult directive. Orientation pulses are not produced until 7–9 days of age. Mother bats nurse only their own young and recognize their infants on the basis of auditory and olfactory cues. A vocal signature is present in the isolation call and appears to manifest itself through the temporal patterning of frequencies. Adult pallid bats possess auditory capabilities similar to those of other echolocating Vespertilionids. Newborn bats show no behavioral or neurophysiological responses to auditory stimuli. Evoked responses were first recorded from the posterior colliculus in a six-day-old bat in response to loud, low-frequency sounds. Absolute sensitivity and frequency range increase rapidly in the maturing bat. By 24 days, the audiogram resembles that of the adult. Except for the first week after birth, the infant bat's vocalizations contain only frequencies which it can hear.