An Examination of Variation in Common Chimpanzee Pant-Hoot Vocalizations for Evidence of Vocal Learning and Developmental Instability
Lankford, Jillian A.
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The distinctive long distance pant-hoot vocalizations of male common chimpanzees, Pan troglodytes, were studied in a captive colony at the Yerkes Regional Primate Research Center in Atlanta, GA to examine inter-population variability and the hypothesis that at least some intra-individual variation in the call could be accounted for by developmental instability (DI). Calls typically consist of four distinctly audible phrases that include an introduction, a build-up, a climax, and a let-down phrase, and it is known that the structure of the calls vary within and between populations. Developmental instability causes deviation from an intended phenotype and may be a cause of at least some variation in call structure. Developmental instability is also known to influence handedness in humans. As the handedness of chimpanzees appears to be similar to that of humans, it was expected that moderately-right-handed chimpanzees (ModR) would exhibit less variation in their pant-hoot calls than non-moderately-righthanded chimpanzees (non-ModR) if DI influences call variation. To test this hypothesis, pant-hoots from male chimpanzees in the Yerkes colony were recorded and acoustic features of over 70 pant-hoots from 18 subjects of known handedness were examined using spectrographic and aural analysis. These features were then compared to vocal features of other chimpanzee populations to examine inter-population variability and the possibility that vocal learning occurs in chimpanzee colonies. Initial results for the 18 subjects (8 ModR, 10 non-ModR) show that a distinct pant-hoot exists within the Yerkes colony. Also, a significant linear relationship between climax duration and number of build-up elements for ModR chimpanzees was found while a visibly different trend emerged for non-ModR chimpanzees. These preliminary results from relatively few subjects provide additional evidence for vocal learning and suggest that variation in this call is indicative of developmental instability.