Mystery Bird: Cassin's Kingbird, Tyrannus vociferans

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[Mystery bird] Cassin’s Kingbird, Tyrannus vociferans, photographed in the central Sonora of Arizona. [I will identify this bird for you tomorrow]
Image: Rick Wright [larger view].

Please name at least one field mark that supports your identification.


Rick Wright, Managing Director of WINGS Birding Tours Worldwide, writes:
Sometimes it’s the lousy views that are the most instructive, and this view — so lousy as to be nearly impolite — is chockfull of information that most of the standard field guides won’t teach you.
I think it’s fairly easy to get this bird, photographed in northwest Mexico, to family. It’s big, long-winged, heavy-bodied, and perched on a wire high against the sky. The olive upperparts and yellow-tinged underparts confirm that we’re looking at one of the kingbirds.
They’re aptly named, in English and in scientificese (Tyrannus, the oligarch), for both their overbearing habits and their jeweled crowns (usually concealed). Distinctive as they are as a group, the kingbirds, especially the yellow-bellied ones, can be an identification challenge, particularly in the tropics, where they (like all tyrant flycatchers) attain their greatest and most bewildering diversity.
It’s bad enough in the American southwest, where this photo was taken in early November. At that season, Thick-billed, Tropical, Western, and Cassin’s Kingbirds come into question; Eastern Kingbird is possible, too, but in contrast to our quiz bird, that species is notably small and obviously black-and-white.
The awkward angle from which this image was obtained virtually forces us to begin at the rear of the bird, not a bad place with yellow-bellied kingbirds. The tail, though foreshortened, is not obviously long, but it is clearly blacker than the wings or back; neither Thick-billed nor Tropical Kingbird shows that much contrast. The finer pattern of the tail deserves attention, too: there is a thin pale outer margin to the outermost rectrix, the classic field-guide field mark for Western Kingbird.
But look closer. That margin is very thin indeed, and even against the light it is obviously dingy, not the clear, bright white of a Western Kingbird’s. And the tips of each of the tail feathers also show a dingy pale tip, creating the impression of a poorly defined terminal band. This tail is fresh — note that the outer tail feathers seem still to be growing — and these pale marks are more obviously than they will be once wear sets in and the tail becomes all dull black.
The tail may have misled us, but the wings will settle the matter. The outermost primary on Western Kingbird is rapier-sharp; here, in contrast, that feather, visible on our mystery bird’s left wing, is blunter. And the secondary coverts of Western Kingbird are quite plain, giving the folded wing a visually smooth appearance; the quiz bird’s coverts are regularly and conspicuously scalloped, making the wing look rough to the eye.
This was one of several dozen Cassin’s Kingbirds staging for roost along a river in central Sonora.
Review all mystery birds to date.

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About GrrlScientist

grrlscientist is the pseudonym of an evolutionary biologist and ornithologist who writes about evolution, ethology, and ecology, especially in birds. After earning a degree in microbiology (thesis focus: virology) and working at the Fred Hutchinson Cancer Research Center in Seattle, she earned her PhD in zoology from the University of Washington in Seattle, where she studied the molecular correlates of testosterone and behaviour in white-crowned sparrows. She then worked a Chapman Postdoctoral Fellow at the American Museum of Natural History in New York City, where she studied the speciation and distribution of lories and other parrots throughout the South Pacific Islands. A discarded scientist, she returned to her roots: writing. Formerly hosted by The Guardian (UK), she now writes about science for Forbes and for the non-profit think tank, the Evolution Institute and she writes podcasts for BirdNote Radio. An avid lifelong birder and aviculturist, she lives with a flock of songbirds and parrots somewhere in Germany.
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0 Responses to Mystery Bird: Cassin's Kingbird, Tyrannus vociferans

  1. It’s either a Cassin’s or a Western Kingbird. The view isn’t great for making the call between the two, but I guess the tail looks more Western (with what looks like it might be pale edges, though again, the view isn’t great; I might be responding mostly to the lighting giving spurious highlights along the righthand edge). I at least don’t see an obvious terminal band on the tail, which would indicate Cassin’s. On the other hand, I think I might be seeing pale edges the wing coverts, which pushes me more in the direction of Cassin’s.
    On balance, I’m going to say Western Kingbird. But if I’m wrong, I’m not going to lose sleep over it.

  2. rick wright says:

    Actually photographed in central Sonora, November.

  3. llewelly says:

    I don’t know what kind of bird it is, but it’s definitely mooning us.

  4. Steve Duncan says:

    I agree with John Callender- Western Kingbird, unless that light edge on the tail is an artifact of the lighting in which case it would be Cassin’s Kingbird.

  5. Jerry Friedman says:

    Western Kingbird. In addition to what others have said, the breast is too pale for a Cassin’s. That’s how I tell them apart–breast color and the contrasting malar are far easier for me to see on these birds than any other mark, except on those occasions when they fly up and spread their tails against the sky.
    It’s hard for me to see how the pale tail edge could be a lighting effect, because at the tip of the tail (where Rick Wright says we should start), it doesn’t seem to follow the edge of the feather that it’s folded under. That upper feather has a much thinner “pale” edge that I think is caused by lighting.

  6. Ian Kinman says:

    I believe that this is a Western Kingbird. It is not a Tropical Kingbird as the tail is not forked. The tail appears to have light edges suggesting a Western Kingbird over a Cassins.
    Ian Kinman

  7. Murray Hansen says:

    late on the scene, but looks like a W. Kingbird to me too: white edges to tail, soft yellow wash (don’t see any chance of reflected light),unmarked underparts; we have the tropical here occasionally over on the coast this time of year; the western and eastern are easily found in eastern WA. (Any chance of Couch’s?” :>)

  8. Hugh McGuinness says:

    WEKI!

  9. Ha! That’s great. Well, chalk up another learning experience for me. Thanks for the explanation. 🙂