Acoustic analysis of wild chimpanzee pant hoots: Do Kibale Forest chimpanzees have an acoustically distinct food arrival pant hoot?

Abstract

Recordings were made of 193 pant hoots given by 6 adult males during ad lib sampling over a 16-month period in 1988 and 1989. The presence or absence of a let-down phase, and acoustic measures of the let-down and climax phases of the calls, were compared for different call contexts to determine if an acoustically distinct pant hoot was given uniquely upon arrival at fruiting trees. The greatest proportion of pant hoots with a let-down (LD pant hoots) occurred immediately upon arrival at fruiting trees. However, LD pant hoots also occurred at other times during feeding bouts. The frequency and duration of the first exhaled element of 19 letdown phases were measured, and four measures were made on the highest pitched element of 49 climax phases: duration, maximum and minimum frequencies, and average frequency. No differences were found in these acoustic measures that distinguished calls given immediately upon arrival at a food tree from calls given later during feeding bouts. Thus no evidence was found that an acoustically distinct pant hoot was given uniquely upon arrival at fruiting trees. However, the analyses did suggest that identifiable pant hoot variants are given in different social contexts. The proportion of LD pant hoots decreased in more interactive social contexts, and other acoustic features may be available to distinguish this pant hoot variant at long distances. We suggest that different pant hoot variants might broadcast information specific to social, as opposed to ecological, context.