This brown-backed, dusky-throated little swallow prefers open areas and nests singly or in small colonies in burrows or crevices, including those in human-made structures. John James Audubon ( Audubon 1838b ) discovered the Northern Rough-winged Swallow in 1819, virtually by accident when he collected a few of what he thought were Bank Swallows (Riparia riparia) in Louisiana. Only with later, closer observations did he determine that he had actually collected representatives of a distinct species.
The Northern Rough-winged Swallow is an aerial forager adept at low-elevation flight over fields and along narrow gullies and other irregular terrain. It feeds over water more than most species of swallows and occasionally picks floating insects from the water surface. Although fairly common throughout its breeding range, which includes virtually all of North America south of southern Canada, it is a bird that is easily missed. Breeding Bird Survey data show that of all North American swallows, this species has by far the fewest individuals counted per route where observed.
This swallow's most distinguishing characteristic is its “rough” primary feather, from which its common name has been derived (see Figure 6). In adults the stiffened barbs of the leading web of the outer primary feather lack terminal barbules. In males the barbs are recurved into minute hooklets, and in the female they are prolonged into a definite, naked point that is little or not at all recurved. In males this produces “a file-like roughness when the finger is drawn along the edge of the quill from base toward tip” ( Ridgway 1904 ). Early taxonomists were so taken with this characteristic that they referred to it in both the genus and species portions of this bird's scientific name. The Greek appellation for the genus, Stelgidopteryx, is a combination of two words meaning “scraper wing,” and the species name of serripennis, assigned by Audubon, is a combination of two Latin words meaning “saw feather.” The possible adaptive significance of this feature remains a mystery.
The taxonomy of the genus Stelgidopteryx is uncertain, in both the number of species and subspecies recognized and their evolutionary relationship to other New World swallows (see Systematics, below). What was once considered a single species, Rough-winged Swallow, ranging from southern Canada to Argentina is now recognized as two species: the Northern Rough-winged Swallow in North America and the Southern Rough-winged Swallow (S. ruficollis) from Panama to Argentina. Some authors maintain that a third species, Ridgway's Rough-winged Swallow (S. ridgwayi) occupies the Yucatán Peninsula.