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First published online October 30, 2009
Journal of Experimental Biology 212, 3719-3727 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.033076

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Vocal and anatomical evidence for two-voiced sound production in the greater sage-grouse Centrocercus urophasianus

Alan H. Krakauer^1,*, Maura Tyrrell¹, Kenna Lehmann¹, Neil Losin², Franz Goller³ and Gail L. Patricelli¹

¹ Department of Evolution and Ecology, University of California, 2320 Storer Hall, One Shields Avenue, Davis, CA 95616, USA
² Department of Ecology and Evolutionary Biology, University of California, 621 Charles E. Young Drive South, Los Angeles, CA 90095, USA
³ Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA

^* Author for correspondence (ahkrakauer{at}ucdavis.edu)

Accepted 5 August 2009

Greater sage-grouse, Centrocercus urophasianus, have been a model system in studies of sexual selection and lek evolution. Mate choice in this species depends on acoustic displays during courtship, yet we know little about how males produce these sounds. Here we present evidence for previously undescribed two-voiced sound production in the sage-grouse. We detected this `double whistle' (DW) using multi-channel audio recordings combined with video recordings of male behavior. Of 28 males examined, all males produced at least one DW during observation; variation in DW production did not correlate with observed male mating success. We examined recordings from six additional populations throughout the species' range and found evidence of DW in all six populations, suggesting that the DW is widespread. To examine the possible mechanism of DW production, we dissected two male and female sage-grouse; the syrinx in both sexes differed noticeably from that of the domestic fowl, and notably had two sound sources where the bronchi join the syrinx. Additionally, we found males possess a region of pliable rings at the base of the trachea, as well as a prominent syringeal muscle that is much reduced or absent in females. Experiments with a live phonating bird will be necessary to determine how the syrinx functions to produce the whistle, and whether the DW might be the result of biphonation of a single sound source. We conclude that undiscovered morphological and behavioral complexity may exist even within well-studied species, and that integrative research approaches may aid in the understanding of this type of complexity.

Key words: acoustic location system, Galliformes, lek, microphone array, syrinx, syringeal muscle

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