title: Acoustic models of orangutan hand-assisted alarm calls.
abstract: Orangutans produce alarm calls called kiss-squeaks, which they sometimes modify by putting a hand in front of their mouth. Through theoretical models and observational evidence, we show that using the hand when making a kiss-squeak alters the acoustics of the production in such a way that more formants per kilohertz are produced. Our theoretical models suggest that cylindrical wave propagation is created with the use of the hand and face as they act as a cylindrical extension of the lips. The use of cylindrical wave propagation in animal calls appears to be extremely rare, but is an effective way to lengthen the acoustic system; it causes the number of resonances per kilohertz to increase. This increase is associated with larger animals, and thus using the hand in kiss-squeak production may be effective in exaggerating the size of the producer. Using the hand appears to be a culturally learned behavior, and therefore orangutans may be able to associate the acoustic effect of using the hand with potentially more effective deterrence of predators.
authors: Artificial Intelligence Laboratory, Vrije Universiteit Brussel, Pleinlaan 2, Brussels 1050, Belgium bart@ai.vub.ac.be.
authors: Bart
authors: B
authors: de Boer
authors: Research Centre in Evolutionary Anthropology and Palaeoecology, School of Natural Sciences & Psychology, Liverpool John Moores University, Byrom Street, Liverpool, UK Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Science Park 904, Amsterdam 1098 XH, The Netherlands.
authors: Serge A
authors: SA
authors: Wich
authors: Pongo Foundation, Papenhoeflaan 91, Oudewater 3421XN, The Netherlands.
authors: Madeleine E
authors: ME
authors: Hardus
authors: Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Science Park 904, Amsterdam 1098 XH, The Netherlands.
authors: Adriano R
authors: AR
authors: Lameira
mesh_terms: D000162:Acoustics; D000818:Animals; D006225:Hand; D007214:Indonesia; D008954:Models, Biological; D011148:Pongo pygmaeus / Q000502:physiology*; D013018:Sound Spectrography; D014828:Vocalization, Animal
keywords: Deception; Kiss-squeak; Orangutan; Size exaggeration; Sound production