Photo Quiz #26 Answer
By Jim Burns
The internet discussion on thrasher distribution which ensued last March when Stuart Healy and I questioned John Prather's sighting of multiple Curve-billeds at the Salome Highway site reiterated two key tenets of bird identification-just because you see a bird doesn't mean you will be able to or have to put a label on it, and just because locals have not recorded a species in an area doesn't mean it may not be seen there. As Stuart so perceptively pointed out, habitats and the bird populations they car can and do change over time.
Fall is when migrant thrashers pass through central Arizona and migrant birders begin to visit the Salome Highway site. Scritching around in the shadows under a bush or scampering away through the desert scrub are typical thrasher sighting scenarios. Thus, thrashers in black and white is a good exercise because it takes us beyond our reliance on color to considerations of shape and structure, which may be all you get if your thrasher isn't teed up and singing in full sunlight as it might be during a late winter/early spring breeding season.
Our eight thrasher species are notoriously difficult because several of them share habitat, plumage characteristics, and structural features. Any thrasher observation should begin with tow precautions. Be meticulous in your evaluation of field marks, and resist the temptation to base identification on preconceived notions and expectations.
A) Good photo, easy bird
Here we see a robust thrasher with a very thick bill, both mandibles decurved, and a peaked crown. We see a light iris and relatively dark plumage, uniform except for the lighter throat and the indistinct, perhaps circular spotting in the breast and belly.
Let's eliminate Brown and Long-billed because their streaking is much more distinct and neat. In fact, let's eliminate these two species from the entire quiz for that reason, but before you leave for south Texas this winter, let me show you my Long-billed slides which I incorrectly labeled "Brown." Thrashers are NEVER as easy as they seem in the guide books!
Nets, let's eliminate thrashers with unmarked underparts, and let's eliminate Sage Thrasher because of that big, honking bill. Now, tell me if this is a Bendire's or a Curve-billed. Some field guides say Bendire's lower mandibles is straight. Sibley says only that it is "straighter." Sibley also says Bendire's has a peaked crown. Most field guides characterize Bendire's spots as arrowhead or triangular, but not all remind you that these spots fade out and become less distinct with wear. Most will tell you Bendire's is shaped like Sage, whereas Curve-billed has a Crissal jizz, but when you're this close anything is going to look big and chesty. And don't forget that juvenile Curved-billeds have shorter bills and lighter irises than adults? So, tell me if this is a Bendire's or a Curve-billed.
Here's the heart of the thrasher matter. This is the best Curve-billed (I observed it both calling and singing) photograph I've ever taken, perhaps the best I've ever seen, and I don't believe you can conclusively determine from this photograph whether this bird is a Bendire's or a Curve-billed. And color wouldn't have helped us a bit! Are you beginning to get the thrasher picture now? This Curve-billed Thrasher was photographed March 1999 in....
B) Good photo, difficult bird
Well, only three of our eight thrashers have unmarked underparts. But, those three share a similar shape, a light throat with strong, dark moustachial markings, a tail longer than Curve-billed, and a bill that is longer and thinner and thus more obviously downcurved than Curve-billed, and a bill that is longer and thinner and thus more obviously downcurved than Curve-billed. Sure, you won't see a California Thrasher in Arizona, but Crissal and Le Conte's have been seen at the Salome Highway site in the same bush, and both occur in the California deserts not far from proper California Thrasher habitat.
If you think this can't be a Le Conte's because it's too dark overall, let me remind you this bird is not frontlit like our first and third birds, but sidelit, flanks and topside shadowed by the front half of its body, An it has a dark eye.
If you think this can't be a Crissal because of that dark eye, let me show you some of my color slides of Crissals wherein the iris appears dark because of the angle of light, and let me give you a quaote from a field guide published in 1985 which says "The Crissal is virtually identical to the California Thrasher."
If you think this can't be a California because the face isn't strongly enough patterned or contrasty enough with the throat, notice that the bird is singing and the wind is blowing big time. The throat feathers are distended and all of the bird's plumage is in disarray. Just two more monkey wrenches in your best case field observation scenario.
Here again is the hear of the thrasher matter. This is a good, close-up shot, but if you don't know where this photograph was taken, the identification of this bird is very problematical, and these same problems can and will occur in the field. In this case color would have been somewhat helpful. In sunlight, even at this angle, I can't imagine the beady black patent leather eye of Le Conte's not standing our more obviously from the pale, plain face. So tell me if this is a California or a Crissal. I don't think you can conclusively decide form this photo.
This California Thrasher was photographed Easter Day 2001 at Lake Hodges north of San Diego. Oh, and that curve-billed in our first photo was taken at Papago Park near the zoo in Phoenix.
C) Bad photo, easy bird
Usually the solution to our final quiz is easier and more to the point by virtue of our considerations of the first tow birds. Thus, we know this thrasher is one of three: Curve-billed, Bendire's, or Sage. Compared to our Curve-billed, this bird appears somewhat smaller, somewhat shorter billed, and the lower mandible, if not straight, does at least appear straighter. We see rounded crown, a light iris and the same indistinct, perhaps circular spotting on the breast and belly.
It wouldn't be hard in field to glance at this bird and think Sage Thrasher. There seems to be a hint of a wingbar, but it could be the play of light. The spotting seems more distinct than we're used to seeing on a Curve-billed or a Bendire's, and remember that the crisp, contrasty spotting on Sage fades out by late summer. But you just can't get past that long, curved bill-too long and curved for any Sage Thrasher
Let's eliminate Sage and go back to the quiz clue. We've had an Arizona thrasher and a California thrasher. Bendire's breed in Utah and New Mexico and can even be found in Nevada and Colorado. Sure, and your preconceived notions and expectations follow you around to every state in the union. This bird is not a Bendire's. This is Toxostoma Curvirostre oberholseri, the Texas race of Curve-billed, photographed near Raymondville, Texas, February 2002.
Compared to our central Arizona Curve-billed T.c. paleri, T.c. oberholseri, is smaller, somewhat shorter billed, shows wingbars like a Sage and tailspots like a Bendire's, and has a lighter ventral back-ground color which makes its spot appear more distinct. To my tin ear the songs sound very similar, but it's a good bet if you netted a Texas Curve-billed and released it in Phoenix it would die without progeny.
These two races of Curve-billed may well be split in the future after further DNA studies.
I'm not sure what Stuart learned from his initial inquiry regarding thrashers at the Salome Highway site, but learned never to question another birder's identification (at least not publicly). That's probably a good lesson for all of us, and here's another one Question carefully every thrasher identification your ever make.