Monday, September 6, 2010
Click on picture(s) for a larger view.
Answer by Tony Leukering
All respondents got to the correct family -- Tyrannidae -- for this week's quiz bird. However, as indicated somewhat by the short number of respondents (on the more difficult quizzes, response rates tend to decline), this one was, as one respondent noted, "evil." Despite any evilness, a plurality of respondents (including our one
regular Brit) did get it correct, but just barely.
The strong whitish fringes to the tertials and the hints of green in the upperparts rule out Say's Phoebe, which has gray-fringed tertials and browner upperparts. Once one is among the type genus of the family (Tyrannus) -- nothing else really matches our bird, the very dark tail and rump contrasting with a much paler back leave us only the options of Cassin's and Western kingbirds. Once there, we need to look at parts very carefully.
Our quiz bird is facing away, so the throat/face contrast is impossible to assess. While the bird's tail seems to lack white edges (Western), it also seems to lack a tannish-white tip (Cassin's). The upperparts really seem too pale and contrast too much with the bird's black rump and the tail really seems black, not the very dark brown of Cassin's. But, why doesn't the tail show white sides? Recall that on the folded tail, the outer feathers are layered under the inner feathers such that what appears to be the outer edge of the tail is not actually the outer edge. Studying the tail closely, we can see that only one tail feather is visible on the bird's left side; well, except for the very tip of another one. Since the innermost tail feathers lie on top, we are definitely NOT seeing the outermost rectrix, unless that very thin white edge on the basal half of the tail is that outermost feather peeking out. Despite not being able to see the bird's tail's edges, we can definitely see the tips of multiple feathers and none of them sport the obvious wide pale tip typical of Cassin's, though there is one -- and only one -- feather showing something of a pale tip.
Below, I provide another view of this Western Kingbird that I took in Logan Co., CO, on 19 June 2010. Another nail in the coffin for an ID as Cassin's may be detected by examining the wing formula -- the number of primary tips visible and the spacing among them on the folded wing. In Western Kingbird, 4-5 primary tips should be visible beyond the longest tertial; our quiz bird shows 4. On the bird's left wing, one can somewhat discern that the distance between the tip of the longest primary and the next-longest visible primary (gap 1) is just a bit shorter than the distance across the next gap (gap 2) between tips up -- toward the inside of -- the wing. Cassin's sports a fairly short lowest gap (gap 1) with the next gap up (gap 2) being very wide.
After 9 quizzes this quarter, Chuck Carlson, Margie Joy, Su Snyder, and Peter Wilkinson are tied for the lead with 7 correct.
Incorrect species provided as answers:
Cassin's Kingbird - 5
Say's Phoebe - 3
Tropical Kingbird - 1
Congratulations to the 6 of 15 getting the quiz correct:
Answer: Western Kingbird