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Behavioral Ecology Advance Access published online on March 17, 2009
Behavioral Ecology, doi:10.1093/beheco/arp028
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© The Author 2009. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Testosterone increases UV reflectance of sexually selected crown plumage in male blue tits

Mark L. Roberts, Erica Ras and Anne Peters

Department of Migration and Immuno-ecology, Max Planck Institute for Ornithology, Vogelwarte Radolfzell, 78315 Radolfzell, Germany

Address correspondence to M.L. Roberts, who is now at Division of Biology, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot, Berkshire SL5 7PY, UK. E-mail: m.l.roberts{at}imperial.ac.uk.


  Abstract

A central assumption of models of sexual selection, including the immunocompetence handicap hypothesis, is that the male sex hormone testosterone (T) is responsible for the expression of male sexual signaling; however, this has been questioned for colorful avian plumage. In this experiment, we manipulated T in juvenile male blue tits (Cyanistes caeruleus) during the molt and measured crown ultraviolet (UV) chroma (a sexually selected trait) immediately after molt and in the following spring during the breeding season, as well as recording preening behavior during spring. We found that males that were implanted with T during the molt had higher crown UV chroma than control males (C-males) in the subsequent breeding season but not immediately after molt. We also found that testosterone-treated males preened more than C-males during the spring but not during the preceding molt. These results suggest not only that T influences plumage coloration during the mate attraction period, possibly by increasing preening behavior, but also that exogenous T administered during the juvenile molt may have organizational effects in the subsequent breeding season. Because our study supports the assumption that T enhances the expression of male sexually selected plumage coloration, the results indicate that T could enforce costliness, and therefore honesty, of male plumage color as a signal of quality to females.

Key words: blue tit, crown UV chroma, molt, preening, sexual signaling, testosterone.

Received 23 May 2008; revised 23 January 2009; accepted 3 February 2009.


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M. Roberts and A. Peters
Is testosterone immunosuppressive in a condition-dependent manner? An experimental test in blue tits
J. Exp. Biol., June 15, 2009; 212(12): 1811 - 1818.
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