Plumage reflectance and the objective assessment of avian sexual dichromatism

I. C. Cuthill, A. T.D. Bennett, J. C. Partridge, E. J. Maier

Research output: Contribution to journalArticlepeer-review

364 Citations (Scopus)


Assessment of color using human vision (or standards based thereon) is central to tests of many evolutionary hypotheses. Yet fundamental differences in color vision between humans and other animals call this approach into question. Here we use techniques for objectively assessing color patterns that avoid reliance on species-specific (e.g., human) perception. Reflectance spectra are the invariant features that we expert the animal's color cognition to have evolved to extract. We performed multivariate analyses on principal components derived from >2,600 reflectance spectra (300-720 nm) sampled in a stratified random design from different body regions of male and female starlings in breeding plumage. Starlings possess spatially complex plumage patterns and extensive areas of iridescence. Our study revealed previously unnotices sex differences in plumage coloration and the nature of iridescent and noniridescent sex differences. Sex differences occurred in some body regions but not others, were more pronounced at some wavelengths (both ultraviolet anti human visible), and involved differences in mean reflectance anti spectral shape. Discriminant analysis based on principal components were sufficient to sex correctly 100% of our sample. If hidden sexual dichromatism is widespread, then it has important implications for classifications of animals as mono- or dimorphic and for taxonomic and conservation purposes.

Original languageEnglish
Pages (from-to)183-200
Number of pages18
JournalAmerican Naturalist
Issue number2
Publication statusPublished - 1 Jan 1999
Externally publishedYes


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