Evol Ecol Res 7: 595-606 (2005)     Full PDF if your library subscribes.

Viability selection against highly ornamented males

Amber J. Keyser1* and Lynn M. Siefferman2

1Prescott Bluebird Recovery Project, 5838 SW Vermont Street, Portland, OR 97219 and  2Department of Biological Sciences, Auburn University, 331 Funchess Hall, Auburn, AL 36830, USA

Author to whom all correspondence should be addressed.
e-mail: keyser@vancouver.wsu.edu


Hypothesis: Variation in ornamental traits, such as plumage coloration, is maintained by the opposing forces of sexual selection (increased ornamentation) and natural selection (decreased ornamentation).

Organisms: A wild population of western bluebirds (Sialia mexicana) in northwestern Oregon which has been the subject of longitudinal population studies since 1988.

Methods: We necropsied 47 adult birds recovered dead in 2002. We measured their plumage coloration with an Ocean Optics S2000 reflectance spectrophotometer. Using Mann-Whitney U-tests with Bonferroni correction, we compared these data to measurements collected from 43 adults recaptured alive.

Results: Necropsies suggested that birds died of an epidemic during 2002. Dead females did not differ from survivors in morphology or plumage. Dead males were significantly more highly ornamented (darker, redder breast patch) than males that survived the epidemic.

Keywords: natural mortality, natural selection, sexual selection, Sialia mexicana, western bluebird, wildlife disease.

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