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A bit harder this time! We have two birds at rather challenging angles, but we do have some advantages. The birds are together, allowing us to compare size and shape and they are both perched on what appears to be a conifer trunk (see, botany is important)-that alone narrows the possibilities considerably.
Let's start with the bird on the right-it certainly seems more straightforward than that thing on the left! Let's look at the posture—the bird is supporting itself with its tail. Brown Creepers do this, but have plain whitish underparts (with some color on the belly and undertail coverts), and a distinctive wing pattern. While creepers are quite variable, they would never have the extensive barring present on our bird.
The other group of birds in North American that routinely prop themselves up with their tail is, of course, the woodpeckers. Here too we can use the pattern of the underparts to eliminate several species. All the flickers have extensively spotted underparts. Most woodpeckers have relatively plain underparts or have barring limited to the undertail coverts, vent and lower belly. Ladder-backed and Nuttall's Woodpeckers are extensively barred below, but both have a more distinctive black and white face pattern and white throats. Arizona Woodpecker is heavily spotted and barred below, but these markings are usually brown. The wings of an Arizona Woodpecker would only show barring on the primaries (not on the wing coverts, as our bird shows) and would have a large white patch on the back of the head and neck. Three-toed Woodpeckers in the Rockies can be heavily barred below but would also have awhile throat and wouldn't snow as many markings on the wings.
The only woodpeckers that really match our bird are the sapsuckers. The traces of yellow on the belly further suggest our bird is a sapsucker. And if we look just to the left of our bird's foot we even see a couple of holes drilled in the tree. What about the Yellow-bellied Sapsucker? Looking at the wings we see our bird lacks that species bold white stripe on the wing coverts. In fact Red-naped, Yellow-bellied and Red-breasted Sapsuckers all have a large white patch on the wing. This leaves us with a female Williamson's Sapsucker.
And now, with one bird down, we have one additional hint about the bird on the left: it is (or rather, was) in the same tree as a Williamson's Sapsucker! We should probably start with western birds, then, so we'll pile that little bit of knowledge away in our memory banks.
We can tell this isn't a woodpecker or a creeper. Aside from being too small, this bird clearly isn't using its tail to prop itself up. Chickadees, Titmice and nuthatches frequently cling to trunks like this, but all of those species are more clearly marked and don't have the diffuse streaks that this bird shows on its flanks. Both kinglets could perch on a tree like this and they have wingbars, but these species are more yellowish and, again, don't have streaking on the flanks.
The combination of streaked flanks and smaller size than the Williamson's Sapsucker actually eliminates a lot of things including: thrushes, flycatchers (unlikely to be seen striking quite this pose) and even wrens (which would have barred, spotted or unmarked flanks).
Some vireos can have some faint streaking on the flanks, but the streaking on our bird seems much too extensive. The only species that comes even close in overall coloration would be Plumbeous Vireo, which would never show flanks like our bird. Sparrows have streaked flanks, but it just doesn't make much sense that one would be on the side of a tree (most also have streaking on the mantle).
In fact, the only group of birds that match our bird in terms of posture, location, size and overall pattern are the warblers.
Now that we think we are dealing with a warbler, let's look at what we can easily see. The comedians (or realists) among you may be thinking, "NOT MUCH!" And while this is sort of true, it isn't completely true. We've already seen how much those streaked flanks do to eliminate other species. And we are dealing with a warbler that is mostly gray, which certainly narrows the field. It has those streaked flanks, two white wingbars, relatively contrasty tertial fringes and wings and a tail that are a bit almost black contrasting darker than the mantle.
The obvious white wingbars get rid of all the warblers in the genus Vermivora. Those in the genus Parula (including Crescent-chested) have olive mantles and no flanks streaking. The only warblers that match well are some of those in the genus Dendroica and Olive Warbler. Olive Warbler looks quite similar, in fact. Except that Olive Warblers usually have a fairly broad white mark at the base of the primaries (like a Black-throated Blue Warbler) and then there's that flank streaking that is lacking in Olive Warblers.
The widespread Yellow-rumped Warbler isn't a bad guess. We can't see this bird's rump, so it could be yellow. The wingbars aren't as extensive as on most Audubon's Warblers, but it could be a Myrtle. But a Yellow-rumped Warbler with this gray of a back should have prominent streaking on the mantle. Those without very diffuse streaking would have decidedly more brownish upperparts.
Blackburnian Warbler has a streaked mantle, but Cerulean Warbler has a plain back that is similar to our bird. But Ceruleans aren't as gray as our bird and they have a much shorter tail. Plus, how many of us have ever seen a Cerulean Warbler creeping up the side of a conifer?
Grace's Warbler is very similar to our bird. The slight tinge of brown shown on the flanks is shown by many first year birds. And yet, those first year birds have more brownish upperparts. Adults should have crisper streaking on the flanks. Even more importantly, the mantle of adult Grace's Warblers would have black streaks. Looking carefully at the close wing, we also see that the scapulars are also uniformly gray without any streaking. Grace's Warbler would show dark streaks on the scapulars (again, first years that lack this streaking should be much browner).
Black-throated Gray Warbler would also appear exceedingly similar to our bird (at least in this view), with a predominately gray back, blackish flank streaks, and double white wingbars. But, again, a Black-throated Gray Warbler without streaking on the mantle and without any dark streaks on the scapulars should appear browner than our bird on the mantle (being immature) and the streaking on the flanks would probably average less prominent for such a bird. Still, from this view I must concede it's a very tough call.
We are left with Yellow-throated Warbler, the only other gray-backed species - even though one would not typically think of this species in association with a Williamson's Sapsucker. One of the better ways to distinguish Yellow-throated Warbler from Grace's Warbler (at least from above) is the largely unstreaked upperparts of Yellow-throated. Furthermore, if we look at the left side of this bird's head we what appears to be a white. Nothing else in the photo suggests that it is odd light hitting the bird there. In fact the entire photo seems to be in rather deep shade. This means this white area is probably real and is exactly where we would expect to see the distinctive white patch at the back of the auriculars on a Yellow-throated Warbler (it is too far down on the bird's head and too broad to be and extension of the supercilium). Yellow-throated Warblers are also quite likely to be seen in a conifer, slowly working along branches and trunks, just as this bird. Of course, has one ever appeared in the same tree as a Williamson's Sapsucker? Yes, at least once–when I photographed this Yellow-throated Warbler in Canon City, Colorado 29 December 2003.
And if you're still not convinced we've include another view of the warbler (and the sapsucker).
The following people (listed by submission date beginning with the earliest) submitted correct answers for the January Bird Photo Quiz—Williamson's Sapsucker and Yellow-throated Warbler:
The graphs below show that most people were able to identify Williamson's Sapsucker correctly but had difficulty with the warbler. We received a number of answers that did not conform to the ABA Checklist format. Please note that answers must consist simply of the Common or English name exactly as it appears in the ABA Checklist.
The photo and answer for this quiz were supplied by Chris Wood.