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First published online July 14, 2008
Journal of Experimental Biology 211, 2423-2430 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.013094
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Quantifying avian sexual dichromatism: a comparison of methods

Jessica K. Armenta*, Peter O. Dunn and Linda A. Whittingham

University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA

* Author for correspondence at present address: Lone Star College – CyFair, Cypress, TX, USA (email: jkarmenta{at}gmail.com)

Accepted 19 May 2008

Recent advances in portable spectrophotometers have allowed researchers to collect quantitative, objective data on colour. There are few comparisons of the different methods used to summarize and analyse spectrophotometer data, however. Using colour data on over 900 species of birds, we compared three methods of calculating sexual dichromatism using spectrophotometer data. We also compared sexual dichromatism calculated from spectrophotometer data, in both the ultraviolet (UV) and bird-visible range, with human estimates of sexual dichromatism. We found that all three methods, principal component analysis, segment classification and colour discriminability, yielded essentially comparable estimates of dichromatism for our extensive sample of birds. Certain methods may be better suited to a particular study depending on the questions addressed and the specific colours examined. We found that human visual estimates of dichromatism were similar to spectrophotometer estimates of dichromatism in the bird-visible range; however, human visual estimates did not predict the extent of UV dichromatism. Therefore, the conclusions of previous studies that relied on human vision to assess sexual dichromatism should be reliable. It is not possible, however, to predict a priori whether a species exhibits UV dichromatism without spectrophotometer measurements.

Key words: colouration, colour discriminability, dichromatism, principal component analysis, segment classification, ultraviolet






© The Company of Biologists Ltd 2008