RESEARCH ARTICLE Nonlinear Acoustics in Pant Hoots of Common Chimpanzees (Pan troglodytes): Frequency Jumps, Subharmonics, Biphonation, and Deterministic Chaos TOBIAS RIEDE 1n , MICHAEL J. OWREN 1 , and ADAM CLARK ARCADI 2 1 Department of Psychology, Cornell University, Ithaca, New York 2 Department of Anthropology, Cornell University, Ithaca, New York The pant hoot calls produced by common chimpanzees (Pan troglodytes) are multi-call vocalizations that have figured prominently in investiga- tions of acoustic communication in this species. Although pant hoots are predominantly harmonically structured, they can exhibit an acoustic complexity that has recently been linked to nonlinearity in the vocal-fold dynamics underlying typical mammalian sound production. We examined the occurrence of these sorts of nonlinear phenomena in pant hoot vocalizations, contrasting quieter and lower-pitched ‘‘introduction’’ components with loud and high-pitched ‘‘climax’’ calls in the same bouts. Spectrographic evidence revealed four kinds of nonlinear phenomena, including discrete frequency jumps, subharmonics, biphonation, and deterministic chaos. While these events were virtually never observed during the introduction, they occurred in more than half of the climax calls. Biphonation was by far the most common phenomenon, followed by subharmonics, chaos, and frequency jumps. Individual callers varied in the degree to which their climax calls exhibited nonlinear phenomena, but were consistent in showing more biphonation than other forms. These outcomes show that nonlinear phenomena are routinely present in chimpanzee pant hoots, and help lay the foundation for investigating the function of such events. Am. J. Primatol. 64:277–291, 2004. r 2004 Wiley-Liss, Inc. Key words: nonhuman primates; nonlinear dynamics; larynx; harmonic; bioacoustics Contract grant sponsor: National Science Foundation; Contract grant number: BNS-8704458; Contract grant sponsor: National Geographic Society; Contract grant number: 3603-87; Contract grant sponsor: Leakey Foundation; Contract grant sponsor: MacArthur Foundation; Contract grant sponsor: Rackham Fellowship Program; Contract grant numbers: 114650; 114465; Contract grant sponsor: National Geographic Society; Contract grant number: 5626-96; Contract grant sponsor: German Academic Exchange Service (DAAD). n Correspondence to: Tobias Riede, Institute of Theoretical Biology, Humboldt-University of Berlin, Invalidenstrasse 43, 10115 Berlin, Germany. E-mail: tobiasriede@web.de Received 16 January 2003; revised 12 June 2004; revision accepted 2 July 2004 DOI 10.1002/ajp.20078 Published online in Wiley InterScience (www.interscience.wiley.com). r 2004 Wiley-Liss, Inc. American Journal of Primatology 64:277–291 (2004)