Bird Watching: Rednecks and Ducks, 1 by Grasmussen

Grasmussen wrote:
Murmur, I had never notice the iridescence on a Goldeneye, before today. The light was nearly perfect at the time. I believe nearly all black feathers can exhibit some degree of iridescence if the light is from the correct angle.

In this shot of a Greater Scaup from this morning there is a greenish gloss on the head. Quoting Stokes Field Guide: "In excellent light, note greenish gloss on the head." (p. 67 Western Guide.)
I had never though of Scaup as iridescent, before today. Guess, I had never taken the time to look closely before.