Acoustic features of tonal ‘‘grunt’’ calls in baboons

Abstract

The acoustic features of ‘‘grunt’’ calls recorded from free-ranging baboons (Papioursinus) in Botswana were investigated. Analysis parameters typical of those used to analyze human speech were employed and these sounds were found to closely resemble speech vowels in several respects. They were brief (approximately 97 ms) and highly tonal with a stable fundamental frequency (approximately 122 Hz.) Like adult human males, baboons are estimated to have a vocal tract length of 17 cm (glottis to lips) and this concordance was reflected in the formant structure of the grunts. Three formants (range 2 to 7) were typically found between 0 and 5 kHz, in a pattern resembling that of the vowel ‘‘schwa.’’ Variation due to individual caller and behavioral context are discussed, as well as the implications of these findings for relationships between nonhuman primate vocal communication and human speech.