I know that "red-shafted" and "yellow-shafted" flickers are no longer considered separate species, because they interbreed freely where their ranges overlap in the mid-section of North America. I know that "pure" yellow-shafts are sometimes seen in the West., and "pure" red-shafts are sometimes seen in the East (although less regularly, I think). I know that "hybrids" of the two races are rather regularly seen in various parts of North America. Nevertheless, in some sixty years of active birding, I had never seen a red-shaft in the East, or a yellow-shaft in the West. Therefore, it was exciting for me to have an obvious "hybrid" show up in our Oregon trees and at our suet feeder about five years ago.
There wasn't any question that it was a hybrid. Under the wings and tail the flicker had the bright yellow-gold plumage of an Eastern bird. It had the red "vee" on the nape of its neck, also characteristic of the "yellow-shaft." But its moustache , which should have been black, was red like a Western flicker, with only a faint edging of black.
The hybrid stuck around all that winter, which was fun. It became more fun the next summer when what was apparently the same bird reappeared, and took up (or continued) residence. A little later in the summer, another hybrid appeared, this one almost wholly "red-shaft," except for the red vee on the back of the neck. Both stayed into, then through, the winter. The next year, there were at least four, and almost certainly five, hybrids. All but one had the red-shaft coloring under wings and tail; all had the "Eastern" neck vee. None had a pure black moustache, but some had enough black feathers to make the facial character bi-colored. All of them came and went through the winter months.
The next year, there were fewer, but two or three continued to show up. It was only this past winter and spring, some five years after the first visitor, that none appeared in the yard.
UPDATE - February 2016
After two years of no flicker "hybirds" in the yard, two showed up last fall and have remained through the winter. One is similar to the flicker pictured above: pretty typical "red-shaft," except for the two-tone red-black moustache. The other has mostly "red-shaft" features, but has a very prominent "yellow-shaft" red crescent mark on the name of the neck. Coincidence that we have "hybirds," again, or are these descendants of the earlier birds?
The pictures below were taken through a window. They aren't great, but they do show the "yellow-shaft" neck cresent.
Update July 2016
An adult male flicker (no "yellow-shaft" characteristics) has shown up at our suet feeder, with two fledglings in tow - a male and a female. After several weeks, the adult still feeds both of them regularly, although both come alone to the feeder on occasion. The young male has the "yellow-shaft" crescent on its neck.
Update January 2017
The fledgling with the red crescent stayed around with parents and sibling for about a month, then disappeared through the fall. In late summer, a male with a two-tone moustache (half black, half red) showed up, and is still around in early January. On 4 January, a male with the "yellow-shaft" crescent used the suet feeder - maybe the local hatchling from 2016, or somebody else? He has visited several times since. Clearly, there's a little bit of the "hybrid" gene pool in our local birds.
Update May 2017
The flicker with the "two-tone" moustache stayed around through January and February, and maybe into early March. We haven't seen him for a month or so, now. A flicker with red neck crescent has been around on and off since first appearing in January. He appears to be a resident, and we have seen him calling and courting with the other flickers.
Update mid-July 2017
"Cressy," the "red-shaft" with the "yellow-shaft" neck crescent, continued to stay around through the spring and early summer. This year's first fledglings are beginning to show up at the suet feeders; it will be interesting to see how/if the "yellow-shaft" genes manifest themselves this year.