About 12 people responded to the Mystery Bird Quiz I posted on September 5th. The guesses that I received comprised of seven different species; Pine Warbler, Blackburnian Warbler, Yellow-rumped Warbler, Blackpoll Warbler, Cape May Warbler, American Pipit, and Varied Thrush. The most votes were for American Pipit and Pine Warbler. Let’s take another look at the photos I had originally posted and pick out some field marks.
From this first photo, we can see a small-sized passerine. Immediate features are the dark eye, an olive-colored patch on the side of the neck, streaky breast, streaky sides of the breast and belly, and white undertail coverts that contrast with the rest of the underside of the bird.
In this second, ‘wings tucked’ flight posture we can see two well-defined wing bars on dark wings, still that rather plain face with a hit of the grayish-olive side of its neck. So far, from these two photos I think its safe to rule out Varied Thrush since that species is boldly patterned and has very obvious long, pale wing stripes running along the length of the wing.
Like I mentioned in the initial post, Drew and I saw this bird fly over us Jo Hayes Vista. As soon as I saw it flying towards us, I reached for my camera and fired off as many shots as I could. I then looked at one of the photos on my camera screen (actually the first photo above), and my first guess was American Pipit but then realized it wasn’t quite right. First off, the bird was lacking white outer tail feathers, although they could just be hidden, after all the photos are terrible quality. American Pipit should have a fairly obvious supercilium that contrasts with the side of the face; this is not shown on this bird. American Pipits also have very bold streaking through the breast and sides of the belly that is very crisp. This bird is showing very uneven and blurred streaking throughout its underside. Furthermore, the bird’s shape just doesn’t look correct; American Pipits are very heavy-fronted whereas this bird is pretty streamline.
No other groups of birds really fits this bird right except for the warblers, so let’s go through the warbler species. This photo was taken in the eastern US, so that narrows it down to about 32 species. If we eliminate all the warblers that don’t show vertical underside streaking we are down to eight species right off the bat: Yellow-rumped, Palm, Magnolia, Black-throated Green, Blackburnian, Pine, Cape May, and Blackpoll.
Yellow-rumped Warbler can be thrown out because, even in fall plumage, they show a pale throat that contrasts with the head and breast. Our bird’s throat doesn’t contrast. In addition, Yellow-rumps don’t undertail coverts that contrast in color with the rest of the underside.Yellow-rumps also show obvious yellow patches in their wingpits.
Palm Warbler is famous for having undertail coverts that stand out, but that’s because their undertail coverts are yellow, so that species is ruled out. Magnolia is also a species we can throw out quick, because in all plumages, they are very yellow underneath and have distinct facial markings. Same goes for Black-throated Green Warbler, which has very distinct facial features, not at all like the mystery bird.
Blackburnian Warbler seems like a good candidate, specifically a young first winter type bird. However, the mystery bird doesn’t show the obvious yellowish supercilium of a young Blackburnian and it also lacks the yellow throat that contrasts with the side of the face. Also, the wing bars don’t look right for Blackburnian, which should show thicker-looking bars.
Eliminating the above birds narrows us down to three very good candidates, Pine, Cape May, and Blackpoll Warbler. Fall adult Pine Warblers show vertical streaking, white undertail coverts, white wing bars, and overall olive coloration. One distinct feature of the Pine Warbler, however are their ‘yellow spectacles’ above and below their eyes. The mystery bird doesn’t show this.
Drew’s first guess was Cape May Warbler, which is a good guess. In the fall, adult female and juvenile Cape May Warbler are very olive in color, have heavily streaking throughout the breast and belly, and show a yellowish coloration on the side of the neck. In late fall, adult male Cape Mays can look pretty similar to adult females. Cape Mays even show have white undertail coverts. Everything seems right for a Cape May except for the fact that Cape May Warblers don’t have obvious wing bars. The adult male, even late in the fall, has a white wing patch. The adult female and juvenile have very hard to see pale edging on their upperwing coverts, but it just doesn’t qualify as full-blown wing bars, at least in my opinion.
That leaves us with one last species, Blackpoll Warbler, which if you haven’t realized yet, is the answer. Fall adults and juveniles are very olive in color, have very obvious white undertail coverts, show very thin yet conspicuous white wing bars, and have vertical streaking throughout their undersides. Let’s take a look at one more of the mystery bird, which may help you to see why it’s a Blackpoll Warbler.
Compare the mystery bird to the bird pictured below, a first winter Blackpoll Warbler that we captured while bird banding last fall in the PSU Arboretum.
Thanks for participating, and if you have any more questions, leave a comment and I can try to get back to you. Thanks!