Ducks have been returning to the San Francisco Bay Area for about a month, many of them in the confusing molt between eclipse plumage and the alternate or "bright" plumage of winter and spring. Of course all birds molt, but I don't remember seeing this take place in such vivid detail as on this subadult male Anna's Hummingbird seen this morning along Strawberry Point during a waterbird survey for the Richardson Bay Audubon Center.
These 3 shots were taken in succession. It was amazing to see the array of colors shown by this individual, with a palette that changed with very small changes in his posture.
Iridescent colors in birds colors produced by the structure of the feather, akin to how colors produced by a thin film of oil on water (interference pattern). Blue colors in birds are also created by feather structure, but by a process that involves the selective scattering of reflected light, based on short wave length.
Those interested in the physical base for these phenomena may want to check these sources:
Why Are Hummingbirds Iridescent? (from Johnsgard book on N.A. Hummingbirds)
The Color of Birds (Stanford)
Structural Color in bird feathers (Wiki, somewhat technical)
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