Infant distress vocalizations in the Southern African Lesser Bushbaby (Galago moholi)

Abstract

Infant lesser bushbabies are typically able, from the earliest age, to utter distress vocalizations which appear to have major adaptive significance. Distress vocalizations of infant G. moholi were analyzed by means of a digital storage oscilloscope. Three kinds of sound analyses were carried out: analysis of the sound wave signal, sequential spectrum analysis, and fast Fourier transformation. We emphasize analysis of the frequency spectrum. Three distress calls were identified-the “click call”, the “crackle”, and the “chirp”-which we report for the first time. Click calls were typically composed of short, high-pitched pulses (clicks) uttered in fast, repetitive sequences with a broad band frequency spectrum containing frequencies up to 60 kHz. These acoustic characteristics appear to be particularly well suited for accurate spatial localization of the sound source. The main function of the click call is apparently to alert and to guide the mother to a lost or endangered infant. These basic acoustic characteristics-related to sound localization-are shared to some extent, with the other two distress calls. However, the three calls appear to represent different degrees of distress, with the click call being the basic, call, the crackle corresponding to a greater degree of distress, and the chirp possibly signaling extreme distress such as physical pain.