Living the Scientific Life (Scientist, Interrupted)

tags: Cassin's Kingbird, Tyrannus vociferans, birds, mystery bird, bird ID quiz

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.