Sexual selection in a socially monogamous bird: Male color predicts paternity success in the mountain bluebird, sialia currucoides

Susan L. Balenger, L. Scott Johnson, Brian S. Masters

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


Ornamental traits are thought to evolve because they give individuals an advantage in securing multiple mates. Thus, the presence of ornamentation among males in many monogamous bird species presents something of a conundrum. Under certain conditions, extra-pair paternity can increase the variance in reproductive success among males, thus increasing the potential for sexual selection to act. We addressed this possibility in the mountain bluebird (Sialia currucoides), a socially monogamous songbird in which males possess brilliant ultraviolet (UV)-blue plumage. Specifically, we asked whether a male's success at siring offspring within his own nest and within the nests of other males was related to his coloration. In pairwise comparisons, males that sired extra-pair offspring were not more colorful than the males that they cuckolded. However, males that sired at least one extra-pair offspring were, on average, brighter and more UV-blue than males that did not sire extra-pair offspring. Brighter, more UV-blue males sired more offspring both with their own mate and tended to sire more offspring with extra-pair mates and thus sired more offspring overall. Our results support the hypothesis that the brilliant UV-blue ornamental plumage of male mountain bluebirds evolved at least in part because it provides males with an advantage in fertilizing the eggs of multiple females.

Original languageEnglish (US)
Pages (from-to)403-411
Number of pages9
JournalBehavioral Ecology and Sociobiology
Issue number3
StatePublished - Jan 2009

Bibliographical note

Funding Information:
Acknowledgments B. Beuf, R. Berry, and the Garber family granted permission to work on their property. D. Newman, the Powderhorn Bluebird Club, and R. Berry allowed us access to their nest boxes at the low-elevation site. H. Golden of the US Forest Service allowed us access to nest boxes at our high elevation site and provided logistical support. B. Beuf provided living accommodations at the low-altitude site and much moral support. R. Young and the staff of Bear Lodge Resort provided accommodations at the high-altitude site. J. Eastman built many of the nest boxes used in this study. B. Johnson, J. Brubaker, and E. Ostlind assisted in the field. Special thanks to L. Siefferman for invaluable help in collecting and analyzing spectral data, as well as for sharing her expertise with regards to bluebird coloration. E. Scully, Q. Lupton, M. Liu, W. Hood, G. Hill, and two reviewers provided comments, which improved the manuscript considerably. Financial support came through grants from Sigma Xi (SLB), Towson University’s Faculty Development and Research Committee and Undergraduate Research Committee and from the National Science Foundation (grants DBI-9732442 and IBN-0316541). To all, we are grateful. All methods contained within this manuscript comply with current laws of the USA.

Copyright 2009 Elsevier B.V., All rights reserved.


  • Extra-pair paternity
  • Mountain bluebird
  • Sexual selection
  • Sialia currucoides
  • Structural plumage color


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