|All photos by Marty Horowitz
All photos above are of a Costa's Hummingbird (male, born this year. A female of any age would have a white throat - thanks to Fred Heath for the correction.)
Marty send this info from David Sibley on iridescence in hummingbirds:
…iridescence in hummingbirds: These are structural colors, not pigment, which means they are reflected by microscopic structural features of the feather surface. The surface of the feather is composed of layers of tiny air bubbles. When light strikes the surface of the feather, some light is reflected from the outer surface, and some light travels through the air bubble and reflects off the inner surface. Light with wavelengths that match the thickness of the air bubble are “amplified” [constructive interference, coherent light] as the reflected waves from the inner surface match up and combine with the reflected waves from the outer surface. Other wavelengths are “out of sync” when they combine after reflecting off both surfaces, and they cancel out.
And a bonus photo from Marty of a Broad-billed female.
A big thanks to Marty for this post!