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Quantifying iridescent coloration in animals: a method for improving repeatability

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Abstract

Quantification of animal colors is important to a variety of fields of research, especially those dealing with visual communication and sexual selection. Most animal colors are easily measured using well-established spectrophotometric techniques. However, the unique characteristics of iridescent colors present particular challenges and opportunities to quantify novel color metrics. Due to the fine-scale angle dependence of iridescent coloration, color metrics, such as hue and brightness, must be measured using methods that allow for repeatable comparison across individuals (e.g., by carefully controlling and measuring viewing geometry). Here, we explain how the optical characteristics of iridescent colors should be considered when developing measurement techniques, describe the pitfalls of some commonly used techniques, and recommend improved methods and metrics (angular degree of color change and breadth of reflectance) for quantifying iridescent color. In particular, most studies of iridescent birds to date have used less than ideal procedures and have not provided repeatability estimates for their methods. For example, we demonstrate here that measuring coloration from overlapping patches of iridescent feathers may be problematic, and we argue against methods that do not carefully control viewing geometry. We recommend measuring iridescence at maximal reflectance angles using an apparatus that allows for sample rotation, and we compare this technique to some other commonly used methods using iridescent gorget and crown feathers from Anna’s hummingbirds (Calypte anna). Our apparatus allows for the quantification of angular color change, and we found that maximal reflectance measurements using single feathers are highly repeatable both within feather samples and among samples within an individual.

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Acknowledgments

We thank Richard Flubacher and the Arizona State University Engineering Machine Shop for patiently helping us design and build our apparatus and Joe Macedonia for contributions to the design of the apparatus. We thank Daniel Osorio for sharing his advice and diagrams of his color measurement apparatus. Three anonymous reviewers greatly improved the quality of this manuscript. MGM was supported by a National Science Foundation Graduate Research Fellowship during the completion of this manuscript. Funding was provided by the College of Liberal Arts and Sciences and School of Life Sciences at Arizona State University.

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Authors and Affiliations

  1. School of Life Sciences, Arizona State University, Tempe, AZ, 85287-4501, USA

    Melissa G. Meadows, Nathan I. Morehouse, Ronald L. Rutowski, Jonathan M. Douglas & Kevin J. McGraw

  2. Institut de Recherche sur la Biologie de l’Insecte, Université de Tours, 37200, Tours, France

    Nathan I. Morehouse

Authors
  1. Melissa G. Meadows
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  2. Nathan I. Morehouse
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  3. Ronald L. Rutowski
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  4. Jonathan M. Douglas
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  5. Kevin J. McGraw
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Correspondence to Melissa G. Meadows.

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Communicated by L. Garamszegi

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Meadows, M.G., Morehouse, N.I., Rutowski, R.L. et al. Quantifying iridescent coloration in animals: a method for improving repeatability. Behav Ecol Sociobiol 65, 1317–1327 (2011). https://doi.org/10.1007/s00265-010-1135-5

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  • DOI: https://doi.org/10.1007/s00265-010-1135-5

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