Beyond colour: consistent variation in near infrared and solar reflectivity in sunbirds (Nectariniidae) |
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Authors: | Matthew D. Shawkey Branislav Igic Svana Rogalla Jonathan Goldenberg Susana Clusella-Trullas Liliana D’Alba |
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Affiliation: | 1.Department of Biology, Evolution and Optics of Nanostructures Group,University of Ghent,Ghent,Belgium;2.Division of Ecology & Evolution, Research School of Biology,Australian National University,Canberra,Australia;3.Department of Botany and Zoology & Centre for Invasion Biology,Stellenbosch University,Stellenbosch,South Africa |
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Abstract: | The visible spectrum represents a fraction of the sun’s radiation, a large portion of which is within the near infrared (NIR). However, wavelengths outside of the visible spectrum that are reflected by coloured tissues have rarely been considered, despite their potential significance to thermal effects. Here, we report the reflectivity from 300 to 2100 nm of differently coloured feathers. We measured reflectivity across the UV-Vis-NIR spectra of different (a) body parts, (b) colour-producing mechanisms and (c) sexes for 252 individuals of 68 sunbird (family: Nectariniidae) species. Breast plumage was the most reflective and cap plumage the least. Female plumage had greater reflectivity than males. Carotenoid-based colours had the greatest reflectivity, followed by non-iridescent and iridescent melanin-based colours. As ordered arrays of melanin-filled organelles (melanosomes) produce iridescent colours, this suggests that nanostructuring may affect reflectance across the spectrum. Our results indicate that differently coloured feathers consistently vary in their thermal, as well as obvious visual, properties. |
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