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White-throated Kingfisher: Non-iridescent colours

on 23rd June 2008

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bklim photographed an adult White-throated Kingfisher (Halcyon smyrnensis) showing its brilliant colourful plumage – dark chestnut, blue and white. In addition, it has a red bill, dark brown iris, red orbital skin and legs. The female may have a slightly paler head and belly while the juvenile’s plumage is slightly duller. Whatever the sex or age, the bird is a spectacular specimen, guaranteed to impress anyone.

There is a popular misconception that the brilliance of the kingfishers’ colours is dependent on the angle of light, a result of iridescence. But iridescence does not come into play here, nor are the colours a direct result of the pigments.

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What are responsible are the microscopic structures of the feather.

The mature feather covering is made up of a hard protein sheath of keratin. Just below this sheath is a layer of keratin cells filled with tiny pockets of air. As white light strikes the feather, the short wavelengths are scattered by the air pockets. As shades of blue (blue, indigo and violet) have the shortest wavelengths, they are scattered the most and in all direction. Thus we see the blue from any angle.

Just below the layer of cells containing the light scattering air pockets are melanin, pigments that absorb most of the longer wavelengths of light. This creates a dark background, thus intensifying the blue we see.

Other non-iridescent colours besides blue are also produced structurally. When the light-scattering air pockets are a bit bigger (bigger than the wavelength of blue light), the result is green (since blue is no longer scattered, and green wavelengths are now scattered the most), as in some parrots.

With even larger air pockets, no wavelengths are scattered, but all are reflected, producing white light and thus plumage that we perceive as white; white does not exist as a pigment in birds.

All images by bklim.

Reference:
Clark, G. A. Jr. (2004). [‘Form and function: The external bird.’]. Pp. 3.1-3.70 in Podulka, S., Rohrbaugh, R.W. Jr & Bonney, R. (eds.) Handbook of bird biology. Ithaca, NY: The Cornell Lab of Ornithology.

This post is a cooperative effort between www.naturepixels.org and BESG to bring the study of bird behaviour through photography to a wider audience.

If you like this post please tap on the Like button at the left bottom of page. Any views and opinions expressed in this article are solely those of the authors/contributors, and are not endorsed by the Lee Kong Chian Natural History Museum (LKCNHM, NUS) or its affiliated institutions. Readers are encouraged to use their discretion before making any decisions or judgements based on the information presented.

YC Wee

Dr Wee played a significant role as a green advocate in Singapore through his extensive involvement in various organizations and committees: as Secretary and Chairman for the Malayan Nature Society (Singapore Branch), and with the Nature Society (Singapore) as founding President (1978-1995). He has also served in the Nature Reserve Board (1987-1989), Nature Reserves Committee (1990-1996), National Council on the Environment/Singapore Environment Council (1992-1996), Work-Group on Nature Conservation (1992) and Inter-Varsity Council on the Environment (1995-1997). He is Patron of the Singapore Gardening Society and was appointed Honorary Museum Associate of the Lee Kong Chian Natural History Museum (LKCNHM) in 2012. In 2005, Dr Wee started the Bird Ecology Study Group. With more than 6,000 entries, the website has become a valuable resource consulted by students, birdwatchers and researchers locally and internationally. The views and opinions expressed in this article are his own, and do not represent those of LKCNHM, the National University of Singapore or its affiliated institutions.

Other posts by YC Wee

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