Mystery Bird: Northern Rough-winged Swallow, Stelgidopteryx serripennis

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[Mystery bird] Northern Rough-winged Swallow, Stelgidopteryx serripennis, photographed in Arizona. [I will identify this bird for you tomorrow]
Image: Richard Ditch, 2006 [larger view].

Date Time Original: 2006:03:12 09:45:40
Exposure Time: 1/249
F-Number: 14.00
ISO: 200
Please name at least one field mark that supports your identification.

Rick Wright, Managing Director of WINGS Birding Tours Worldwide, writes:
Look at those wings! They’re obviously long, and we can roughly quantify their length using a formula known as “primary projection,” the relation between the length of the longest tertial and the distance to which the primaries extend beyond that tertial on the folded wing. I’ll let you do the measuring yourself, but what is clear is that that is one mighty PP, with the wingtip protruding well beyond even the end of the tail. Among small birds, this is seen only in hummingbirds, swifts, and swallows.
Hummingbirds are, I think, pretty easily ruled out, and the fact that our mystery bird is so comfortably perched on a twig also eliminates the swifts. So we’re left with a hirundinid (not, please, a “hirundine,” a name that refers only to swallows of the genus Hirundo). Perched swallows and martins are as a rule more difficult than the same birds in flight, when plumage patterns and general aspect are more easily observed, but this individual isn’t going to cause us any problems. In North America north of Mexico, the only swallow this plain (which is not the same as unbeautiful) is the Northern Rough-winged Swallow. Brown-backed Tree Swallows can be eliminated from consideration by the absence of a clear demarcation between the side of the head and the throat, which on a Tree Swallow would be strikingly dark and strikingly white, respectively. A Bank Swallow would also show a clearer face pattern, the white of the throat curling up to surround the darker auriculars, and would be more obviously marked beneath with a narrow, well-defined breast band; the upperparts of that species are also more contrasting, the back and rump noticeably paler than the wings. The Progne martins are much bulkier; Purple Martin, the only regularly occurring member of the genus in the US and Canada, is darker backed and darker breasted, with a contrasting nape band. In addition to its superior size, Brown-chested Martin — a species on the move that has now occurred in Massachusetts, New Jersey, Arizona, Maryland, Illinois, and probably Florida — would show long white undertail coverts, a contrasty face pattern, and from most angles a breast band recalling that of a Bank Swallow.
Northern Rough-winged Swallow is one of those little birds with an enormous name. It owes the “northern” part to the existence of two other Stelgidopteryx species in tropical America. Our mystery bird lacks the white lore spots of Ridgway’s Rough-wing, and does not show the orangish throat and (usually) paler rump of a Southern Rough-wing.
What about the rest of the bird’s name, though? “Rough-winged” is a straightforward translation of both the genus name, Stelgidopteryx, and the specific epithet, serripennis, of Northern Rough-winged Swallow. The barbs at the tip of the outermost primary lack barbules, making them odd little stiff hooks; the function of this structure is completely unknown — the very amusing assertion in a recent issue of one of the birding magazines to the contrary.
Review all mystery birds to date.


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: Northern Rough-winged Swallow, Stelgidopteryx serripennis

  1. I’m going with a juvenile Violet-green Swallow, based mainly on Sibley’s “wingtips project beyond tail tip”. Though the Sibley illustration shows more projection than this bird does, and I could see myself being convinced that this is just an odd posture of a different species that is tending to make the wingtip projection seem greater than it is. But this bird’s “dusky face” seems pretty close to the Sibley illustration of the juvenile Violet-green, too.

  2. BA says:

    Think JC’s probably right. Definitely a Swallow with wings like that but it is hard to see the face and VG’s seem more black than brown but no white above the eye so maybe a bank or cliff swallow. Forced to choose I’d stick with VG.

  3. Jim says:

    Instead of the not so obvious ID, I immediately thought Rough-winged Swallow was the easiest choice. The small size, tiny bill and relatively long pointed wings would say this bird is some kind of swallow. The uniform brown upperparts and the off white underparts with the grayish wash across the chest would support Rough-winged. March 12 would seem to be early for any juvenile. The tail seems short compared to the wing extension – are the tail feathers growing in after a molt or something?

  4. Actually, JC’s wrong again. But I only know that because I checked the answer in the back of the book.

  5. Albatrossity says:

    It’s not a juvenile regardless of the date; the feathers are much too abraded.
    So that leaves Northern Rough-winged Swallow. Brown back, lighter throat, indistinct dun-colored upper breast are consistent with that ID as well.

  6. The Ridger says:

    I’m going with Northern Rough-winged Swallow, based on the coloring – especially the breast – and the wing shape.

  7. Larry Gardella says:

    The bird looks dark for a Northern Rough-winged and a bit too long in the wing. However, the white on the throat is far too restricted for a Tree Swallow (even if a March juvenile were within the realm of possibility.) On the basis of the brown overall color and the grayish breast, I agree on Northern Rough-winged.