To what species is the indicated bird (red arrow pointing at its head) referable?

There are at least two features that often distinguish between skilled, experienced birders and others when it comes to large flocks of birds. The first is the understanding that just because many or most of the individuals of a large flock of birds appear to be referable to the same species does not necessarily mean that such an assumption is true for the entire flock. I have many, many times seen a skilled and dogged observer find the proverbial needle in the haystack, such as the single Brant among a large flock of Canada and Cackling geese or the single Palm Warbler among a huge flock of wintering Yellow-rumpeds.

The second feature, and one that may be even more critical when perusing a flock such as that depicted in this quiz photo, is knowing two important things: What species are most likely in such a flock at that time and place and all the identification features that might permit finding the oddball. This is particularly true for flighty flocks of birds that land and fly, land and fly, as one might get only one brief look at a critical feature, whether the precise tail pattern, leg color, or the distribution of white in the wing coverts.

So, what is the depicted bird? Obviously – at least, I hope it’s obvious, determining the identification of the other individuals in the flock is of critical importance.

What species is represented here?