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<\/p>\nThe cause(es) of plumage coloration in birds isn’t as straightforward as it might first appear.<\/p>\n
Most\u00a0plumage colors are caused by the presence, absence and relative\u00a0concentration of melanin in the feathers but\u00a0in some species\u00a0colors depend on the structure of the feathers (structural colors).\u00a0 For example, blue colors in birds (Indigo Bunting,\u00a0Stellar’s Jay, Mountain Bluebird)\u00a0are almost always caused by microscopic air pockets in feather barbs that produce a specific, non-iridescent color.\u00a0 In normal light a feather of one of these birds will appear blue but if you hold the feather up to back light its true brown color caused by melanin will appear.<\/p>\n
Another type of structural color in some species\u00a0is\u00a0produced when light in the ultraviolet range is reflected back.\u00a0 Some birds can see ultraviolet light so their colors appear quite different to them than to us.<\/p>\n
But most structural colors in birds are iridescent.\u00a0 Iridescence is caused when the microscopic feather structure of certain birds acts as a prism, splitting the light into its component colors (diffraction).\u00a0 The brilliantly colored gorget of many hummingbirds is a well-known example.<\/p>\n
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But in order for the iridescence to be seen the light must strike the bird at particular light angles.\u00a0 If it doesn’t the color that you see is the one caused by melanin, not diffraction.<\/p>\n
The Black-billed Magpie is an example of a highly iridescent bird whose brilliant colors aren’t seen unless the light angle on them is just right.\u00a0 I love to capture that iridescence in my photos\u00a0but it isn’t easy and it’s a matter of degree.\u00a0 Typically, my shots of the species look like this –\u00a0 only the blacks and whites\u00a0are showing\u00a0(this bird is delivering a rabbitbrush twig to the nest).<\/p>\n
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Sometimes you get a small hint of the iridescence as in some of the wing flight feathers of this magpie with a beak-full of mud for its nest.<\/p>\n
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But very occasionally the iridescent colors really explode.\u00a0 I took this shot a few weeks ago\u00a0on Antelope Island\u00a0and I don’t think I’ve ever seen this much color on a perched magpie.\u00a0 In this species the feather structure that causes iridescence is found almost exclusively in the blacks of the wings and tail.\u00a0 Maybe next time I’ll get a similar shot without such a cluttered setting.<\/p>\n
When these birds are nest-building they often fly into it from the same direction (especially if there’s a breeze) so I often experiment with the angle I park\u00a0my pickup relative to the position of the\u00a0nest and sun in an attempt to maximize iridescence in the birds.\u00a0 So far I haven’t found a magic formula for increasing those colors.<\/p>\n