Bill colour and correlates of male quality in blackbirds: an analysis using canonical ordination

Behavioural Processes
A BrightP D Cuming

Abstract

Carotenoid-dependent plumage displays are widely assumed to be honest indicators of individual health or quality, which are used as cues during mate choice and/or agonistic signalling. Despite the fact that red, yellow and orange pigmentation of bills is common, and also variable between individuals, comparatively little is known about bill colouration as a condition-dependent trait. Furthermore, many studies of avian colouration are confounded by the lack of objective colour quantification and the use of overly simplistic univariate techniques for analysis of the relationship between the condition-dependent trait and individual quality variables. In this study, we correlated male blackbird bill colour (a likely carotenoid-dependent sexually selected trait) with body/condition variables that reflect male quality. We measured bill colour using photometric techniques, thus ensuring objectivity. The data were analysed using the multivariate statistical techniques of canonical ordination. Analyses based on reflectance spectra of male blackbird bill samples and colour components (i.e. hue, chroma and brightness) derived from the reflectance spectra were very similar. Analysing the entire reflectance spectra of blackbird bill samples...Continue Reading

References

Jan 1, 1995·Reproduction, Fertility, and Development·T R Birkhead
Oct 25, 2001·Proceedings. Biological Sciences·S M PearnI C Cuthill
Feb 20, 2003·Proceedings. Biological Sciences·Franziska HausmannIan P F Owens
Apr 5, 2003·Science·Bruno FaivreGabriele Sorci
Dec 1, 1998·Trends in Ecology & Evolution·V A Olson, I P Owens

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