Fall is here (for birders, anyway) and warbler migration is underway! We thought it might be a good time to try a quiz on one of the more frequently confused warblers... here it is:
Quiz photos can be a little weird since you only get one look at the bird, and they lack all the other useful cues we use when birding like habitat, behavior, probability, etc...but that's part of the fun! Let's supplement a little here - this bird seems smallish, it's actively picking insects out of this low cedar, and it's in Cape May, NJ in September. Once or twice we see it chase another warbler away from the branch it's on. So now that the scene is set, let's get started.
First, this is a drab bird. It’s mostly gray, with some greenish/yellowish tinging. The first issue with this bird is finding ANY field marks! Actually, that impression of a "lack" of field marks is a good clue, and is a common experience with this bird.
Looking at the finders in the Warbler Guide, we see a few possibilities...
So what can we look at that might narrow down our choices? Let's get beyond the "plain gray" thing and see what we can see...the bird has a fine pointy bill, and it looks slightly drooped or decurved. There is some blurry streaking that goes through the flanks, and maybe the faintest, patchy yellow tinge around the breast. If I look at the finder, I can eliminate the birds that don't have distinct streaking:
I see two other birds I can eliminate here...the Yellow-rumped Warbler (Myrtle) has yellow shoulder patches, and a white malar/throat, which our bird lacks, and the Palm Warbler has a yellow undertail and wide supercilium, while our bird's undertail is white; andonly has an eyeline and eye arcs. Also, Palm Warbler is a habitual tail-pumper, and this bird isn't doing that.
So now we're down to three birds: Blackburnian, Blackpoll and Cape May.
Let's look at the comparison page for Cape May Warbler...we can see that all the birds we looked at in the finder are here.
There are a couple more details about this bird that I think will confirm our ID. First, look at the wings - see the greenish edging on the flight feathers? Also note that there is actually a greenish-yellow rump on this bird. Both those marks are excellent...the greenish edging to the feathers is diagnostic for a grayish bird. The yellow rump is shared only by Yellow-rumped Warbler (which we eliminated) and Magnolia Warbler (whose rump is a brighter yellow, and is actually higher up on the back...the base of the rump is black). So I think we've arrived...it's a Cape May Warbler!
The next time a drab gray warbler turns up, we now know to check a couple of things... greenish wing edging? Yellow-green rump? Fine, pointy bill on a smallish bird? Aggressive behavior (hence the nickname "Tiger of the Woods")? Blurry streaks in the flanks, often with a little patchy yellow in the breast? And finally (not shown in the quiz photo), fine streaking that extends across the upper breast? All of these are good indicators that your otherwise drab, gray warbler is a Cape May. Let's hope we see lots of these great birds this fall!