Image: Richard Ditch, 2006 [larger view].
Date Time Original: 2006:03:12 09:45:40
Exposure Time: 1/249
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.