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Contemporary divergence of island bird plumage

Authors

  • Julian D. Avery,

    1. Dept of Ecology, Evolution, and Natural Resources, Rutgers Univ., 14 College Farm Road, New Brunswick, NJ 08901, USA.
    2. Dept of Ecosystem Science and Management, Pennsylvania State Univ., State College, PA 16801, USA.
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  • Phillip Cassey,

    1. School of Earth and Environmental Sciences, Univ. of Adelaide, SA 5005, Australia.
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  • Julie L. Lockwood

    1. Dept of Ecology, Evolution, and Natural Resources, Rutgers Univ., 14 College Farm Road, New Brunswick, NJ 08901, USA.
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J. D. Avery, Dept of Ecology, Evolution, and Natural Resources, Rutgers Univ., 14 College Farm Road, New Brunswick, NJ 08901, USA. Present address for JDA: Dept of Ecosystem Science and Management, Pennsylvania State Univ., State College, PA 16801, USA. E-mail: jda121@psu.edu

Abstract

Although the diversity in avian plumage coloration is striking, there is little known about the rate with which colour diverges. Eastern bluebirds Sialia sialis bermudensis on the island of Bermuda are considered endemic based upon differences in coloration from the mainland, but recent molecular evidence suggests they established on the island only 400 yr ago. We explored sexual dichromatism and colour divergence in this isolated population, thus providing one of the few quantitative accounts of contemporary plumage change. Contrary to expectations that sexual dichromatism would decrease in this sedentary island population, we found that males and females have increased plumage ornamentation in a coordinated fashion that acts to preserve sexual dichromatism, while plumage colour is also altered to become brighter and bluer. These differences were in place at least 100 yr ago based upon a separate analysis of museum specimens. Our results provide insight into the divergence of plumage colour in an incipient species, and we show the remarkable extent to which plumage colour can change over contemporary time frames.

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