Quick! Think of some of the notorious species-pairs for ABA Area birders. Chances are, You thought of one or more of the following:
1. Downy and Hairy woodpeckers
2. Alder and Willow flycatchers
3. Western and Semipalmated sandpipers
4. Cooper’s and Sharp-shinned hawks
5. Bay-breasted and Blackpoll warblers (in fall)
6. Sooty and Short-tailed shearwaters
7. Rufous and Allen’s hummingbirds
8. Iceland and Thayer’s gulls
9. Western and Eastern screech-owls
10. Hoary and Common redpolls
I’m not saying you thought of all 10. But at least one, yes? Depending on where you live, how long you’ve been birding, and which field guide you use, you’ve probably been vexed by one or more of the preceding.
We could continue the exercise and come up with a list of the Top 25 confusing species-pairs for North American birders.
I wonder how many of us would name this species-pair:
Chimney and Vaux’s swifts
I think we tend not to ponder this pairing for the simple reason that we can ID the birds by geography alone. Geography is, of course, critical for bird ID. If we see a brown-headed pygmy of a nuthatch in Georgia, we know it’s a Brown-headed Nuthatch; if we see such a bird in Nevada, we know it’s a Pygmy Nuthatch. Range is almost always the best way to separate the closely related but geographically distant Brown-headed and Pygmy nuthatches.
So it is with Chaetura swifts, right? East of the Rockies: Chimney. West of the Rockies: Vaux’s. A Chaetura swift in Philadelphia is a Chimney; a Chaetura in Portland is a Vaux’s. (“Chaetura,” you ask? It’s a genus of swift. Two species–Chimney and Vaux’s–occur in the ABA Area.)
The problem with the ID-by-geography approach is that it’s far from foolproof in the case of North America’s Chaetura swifts. When I moved out West, I was surprised to learn that the common summertime Chaetura in Los Angeles is–wait for it–the Chimney Swift! And birders with the famous 4th edition of Peterson’s Field Guide know that the Vaux’s Swift is very rare but probably regular in Louisiana from fall through spring.
Swifts migrate great distances, and they have tremendously powerful wings. The ID-by-geography approach is usually a safe bet for Brown-headed and Pygmy nuthatches (although the folks in Oklahoma, where both species have occurred, might disagree), but it’s risky with North America’s Chaetura swifts.
Which brings us to the matter of the New Photo Quiz in the July/August 2013 Birding. Below I’ll post the three quiz images. Ordinarily, we tell you the location and date of our quiz images; after all, in most real-life birding situations, you tend to know where you are and what the date is. For this quiz, we’ll tell you that all three images are from spring. But let’s not reveal the locations of these swifts. Let’s see if we can ID them on the basis of what they look like. Remember: This *could* be Los Angeles in May or New Orleans in April!
As usual, I have a request. Please tell us why you think the birds are what you think they are. What are you seeing–field marks, size and shape, behavior, whatever–that has led you to your identification?
Tom Johnson’s official answers will appear in the September/October 2013 Birding. But let’s first see if we can work this out together online.
Update–Oct. 20, 2013.
If you don’t want to see the answers to this quiz, either back up immediately or skip down into the comments. Ready? Here goes . . .
As many of us have already figured out, Quiz Bird A is a Vaux’s Swift, Quiz Bird B is a Chimney Swift, and Quiz Bird C is a Chimney Swift. But here’s a twist: Quiz Birds B and C are the same individual bird.
Tom Johnson’s thorough analysis of these quiz birds appears in the print version of the September/October 2013 Birding, pp. 48-52. There’s a lot of great info in Tom’s article, including a summary of 9 characters for separating the ABA Area’s two Chaetura swifts, an eye-opening look at “Modified Aspect Ratio,” and a dazzling photo salon of incredible close-ups of swifts in flight.