Monday, April 25, 2011
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Solution by Tony Leukering
This week's quiz bird, an Empidonax flycatcher, caused much less consternation than I had expected; at least for the respondents. The extensive yellow on the mandible and the blackish legs rule out various vireo options. The long bill suggests something other than the various short-billed Empies (Least, Yellow-bellied, Hammond's), but the absolute measurements don't really differ all that much and relying on that feature might take us somewhere we don't want to be. The dull coloration, however, can probably help us out a lot.
When identifying Empidonax, it is important to keep molt strategies in the back of your mind. Adults of some species conduct their prebasic molt on the breeding grounds, and some on the winter grounds. Thus, in fall, the state of plumage wear in ADULT empies can rule various species in or out. At that time, age can generally be determined by the color of the wing bars, with those of adults being white, juvs buffy. Additionally, and just to confuse things, juvs of some species conduct their prebasic molts on the summer grounds. Details on timing and location of various molts in these species can be found in Peter Pyle's Identification Guide to North American Birds, part I (1997; Slate Creek Press; Bolinas, CA).
Regardless of all of the above, our bird's wing bars are not only white, they are quite thick, which should tell us that the plumage is fresh (recall that white bits on feathers wear fairly quickly). And, since the bird is in a mesquite, we can suspect that it is a member either of one of the more southwesterly-breeding species and/or is on or near winter grounds. Since the plumage is fresh, the fact that the bird is very dull, with virtually no green and very little yellow evident, we should be able to make a good stab at the bird's ID: Gray Flycatcher. Looking to confirm that tentative ID, we note that the wings are short (there is little in the way of primary projection) and the tail looks at least longish. Finally, the bill appears longish and thin and then there's that extensive yellow that is cut off fairly abruptly near the tip. All of these features are consistent with our tentative ID. Now, we need to be certain that we can rule OUT other species.
In the West, many birders have trouble separating Dusky and Hammond's flycatchers when Dusky vs. Gray is much, much more difficult of an ID problem. That is because Dusky and Hammond's share virtually no shape characters, whereas Dusky and Gray are so similar in those respects. Granted, Gray Flycatcher has a behavioral character that absolutely identifies it (among Empidonax), but that's not so helpful in this quiz. So, while Dusky Flycatchers can approach our bird's plumage appearance (little green or yellow), that only happens when very worn. Finally, though mandible pattern on Dusky Flycatcher is exceedingly variable, they never (ah, that fateful 'never') sport such a strong demarcation between dark and light.
Steve Mlodinow took this picture of a wintering Gray Flycatcher in Santiago, Baja California Sur, Mexico, on 2 November 2010.
One respondent neglected to capitalize the 'f,' so that person's response was precluded from being correct for the competition.
Incorrect species provided as answers:
Bell's Vireo - 1
Yellow-bellied Flycatcher - 1
Dusky Flycatcher - 2
Congratulations to the 19 of 23 getting the quiz correct:
Answer: Gray Flycatcher