Structural Color in Bucephala, the Ox-headed Ducks

In the right light the back on a Lewis's Woodpecker shines with a dark green gloss, inspiring me to look more closely at the colors that are sometimes seen when viewing black or brown feathers on birds.

Some bird colors are produced by the pigments in the feathers, including melanins (blacks and browns) and caretenoids (oranges, reds, yellows). We see other colors in birds because of the microscopic structure of the feather, such as the blues of our jays, bluebirds and buntings. Most striking of all are the iridescent colors reflected back to us when light strikes the black feathers of some birds at just the right angle, such that the white light is broken by the feather's microstructure and certain wavelengths are selectively "reinforced" and reflected back as an "interference pattern", like the brilliant green we see on the black head of the male Mallard and the awesome ruby of a hummingbird's gorget, or in this case, the male Bufflehead.

The Bufflehead is a small sea duck in the tribe Mergini. The male Bufflehead with his bright black and white pattern can easily be distinguished at a distance. No so easy to see, and especially hard to capture in a photo, is the rainbow of iridescent colors produced when light strikes his head at just the right angle, as shown in this shot from Lloyd Lake in Golden Gate Park on January 7th. It's almost appears like a prism has split the light into a bufflehead rainbow. Maybe not the sharpest shot, but a colorful one.

A few years at Berkeley's Aquatic Park I spotted a male Bufflehead close enough for a good photo. Note how the array of spectral colors is similar, and how it includes a greater variety than average in black iridescent birds.

The Goldeneyes are close relatives of the Bufflehead, sharing the black-and-white color scheme. And as with the Bufflehead we can seen a color gloss or sheen on the head of the males if the light is just right. At Lake Solano Park (Putah Creek) Valley we sad a good number of Buffleheads and Goldeneyes upstream from the bridge across the creek. The distance (75-100') required that images be cropped, so not the sharpest, but the lighting was electric. The Barrow's Goldeneye male with brilliant his electric indigo sheen contrasted sharply with the emerald green flash on the Common Goldeneye as they swam together.

The Barrow's male is easy to identify, even if the white facial crescent is hidden. The white on his back is broken into a series of white lozenges, as compared with the white "piano keys" on the Common. The forehead usually appears much steeper than the Common's, and the downward pointing black spur at the shoulder is also distinctive. "Indigo" can mean different things to each of us, but is sometimes described as a color between blue and violet. More on Indigo. Some might call it a midnight blue, but whatever the name it was striking in this mid-morning light.

And another showing the white spots on the back of both Goldeneyes:

The Common Goldeneye male is equally distinctive, with the white ovoid cheek patch and larger white patches on the inner sections the wings (secondaries).