Yellow-shafted Flickers in the Bay Area
I wanted to address an issue that has been very prevalent this Fall/Winter, particular in eBird, in the Bay Area and other parts of California--the status and identification of "Yellow-shafted" Northern Flickers. This taxa of Flicker breeds from the Great Plains east and occurs as a rare but somewhat regular vagrant in California.
Flickers with Yellow underwings and undertails are not particularly uncommon in much of the Bay Area and finding one or two in a whole day of birding is not really unexpected. The vast majority of these birds, however, are intergrade "Red-shafted" x "Yellow-shafted" Flickers. These intergrades often outnumber (seemingly) pure Yellow-shafteds by more than 10:1 and while intergrades are not really a rarity in the Bay Area, "pure" Yellow-shafteds very much are.
There have been many reports in eBird across all counties of the Bay Area of "Yellow-shafted" Flickers with the sole comments that they had yellow underwings. While a flicker with yellow underwings is definitely not a "Red-shafted" Flicker, wing color proves nothing about a bird being a pure Yellow-shafted Flicker. Below are some of the features which can be used to accurately determine if a bird is a "pure" Yellow-shafted Flicker:
1) Head Pattern. The absolute most definitive feature for flicker identification is the head and face pattern. Red-shafted birds have brown around the face right around the bill (often extending to a brownish malar on female Red-shafteds) and gray on the rest of the head. Yellow-shafted birds have clean peach-colored throat and face extending from above the bill to the top of the breast. /If the birds throat has any gray at all, its a hybrid/ (for birds with yellow underwings).
For reference, a "pure" Yellow-shafted Flicker face will look, more or less, exactly like this https://macaulaylibrary.org/asset/83265481 plus or minus the black malar depending on sex.
2) Malar. For male flickers malar is a quick way to separate the two subspecies. Red-shafteds have red malars, and Yellow-shafteds have black malars. This by no means a flicker with an all black malar is a Yellow-shafted. It simply means that any male flicker with a mix of red and black in the malar is automatically a hybrid, and also that /any seemingly pure yellow-shafted flicker, even if it ticks all of the boxes in point one, is a hybrid if there is even a single red feather in the malar/.
3) Nape crescent. All plumages of Yellow-shafted have a red crescent on the nape, whereas Red-shafteds do not. Hybrids can have nape crescents, but sometimes they are reduced. /A full red nape crescent will be found on all pure Yellow-shafted birds/
4) Underwing color. While yellow underwings means nothing towards a bird being a pure Yellow-shafted, a/hint of salmon is damning trait for any potentially pure birds/. While there are birds in parts of the country which consume high-carotin berries in the winter and as such get a touch of reddish under the wing, I don't believe it is really worth considering these birds in California.
An important point to realize with the identification of flickers is that, while pure Red- and Yellow-shafted Flickers show very specific and unchanging field marks, intergrades are exceptionally diverse. That is, a hybrid could look exactly like a male Red-shafted Flicker other than having a red nape crescent or a hybrid could look exactly like a pure Yellow-shafted Flicker with a red feather or two in its malar. So, when in doubt, err on the side of caution with any seemingly "Yellow-shafted" Flicker
To reiterate the points a flicker with Yellow underwings in the Bay Area is very likely to be an intergrade, but if it seems like it may be a "pure" yellow shafted you have to look very carefully at a number of features in order to be certain of that identification.
If you are submitting a "Yellow-shafted" Flicker to eBird, please keep the above points in mind, and try to address the specifically with regards to your bird.
Anyway, hope this is useful for anyone interested in sorting out the mixed back of California Flickers.
Happy CBC season,
San Francisco, CA