Acoustic models of orangutan hand-assisted alarm calls
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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.
De Boer , B , Wich , S A , Hardus , M E & Lameira , A R 2015 , ' Acoustic models of orangutan hand-assisted alarm calls ' Journal of Experimental Biology , vol 218 , no. 6 , pp. 907-914 . DOI: 10.1242/jeb.110577
Journal of Experimental Biology
© 2015 The Author(s). Published by The Company of Biologists Ltd. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://doi.org/10.1242/jeb.110577
B.d.B. was funded by the European research council starting grant ABACUS project and the Innoviris ‘Brains back to Brussels’ programme. S.A.W. was funded by the Netherlands Organisation for Scientific Research NWO. A.R.L. was funded by the Menken Funds (University of Amsterdam).
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