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Andrew
Griswold, Director of EcoTravel
35 Pratt Street, Suite 201
Essex 06426
860-767-0660
Fax: 860-767-9988
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Copyright
2006 All Rights Reserved to Connecticut Audubon Society
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Nature Photos of the Week
June 13, 2007
Birds in Blue!
Most avian colors are the result of different types of pigments that are deposited into the developing feather. However, pigments alone do not produce all avian feather colors. Blues and whites typically result from small changes in feather structure that alters their light reflective properties. These fundamental modifications cause blue light to be selectively reflected from the feather surface in the case of blue feathers, while white feathers reflect all visible light. In short, blues and whites are structural colors, or schemochromes.
Blue coloring in most bird species results from preferential scattering of blue light by the feather structure. When a blue feather is observed under a powerful microscope, the surface layer of keratin appears cloudy or milky due to the presence of small air cavities. A cross-section of the feather reveals an underlying layer of melanin granules and tiny air pockets in the middle of the feather barb. These small air cavities act like tiny particles because they selectively scatter blue light while the melanin granules absorb longer wavelengths of light, intensifying the blue. Structural differences are immediately obvious when a red feather, which derives its color from pigments, is viewed under the same microscope. The surface of the red feather is transparent and colorless while the underlying structures are filled with red pigment granules that reflect only red light
Link to more about: Why are Bluebirds Blue? by Devorah Bennu
Little Blue Heron, Egretta caerulea © 2006 Heather Campbell
Florida, USA
Indigo Bunting , Passerina cyanea © 2007 David Earls
USA
Eastern Bluebird, Sialia sialis © 2007 Mark Jankura
Shelton, CT
Purple Gallinule , Porphurula martinica © 2007 Mark Jankura
Stratford, CT
Mountain Bluebird , Sialia currucoides © 2006 Mary Cuyler
Colorado, USA
Blue-footed Boobie, Sula nebouxi © 2007 John McGinley
Galapagos Islands, Ecuador
"It's not my feathers! Just my feet!"
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