April 2017

Vol. 45, No. 2

Front Cover: April 2017

Rough-winged Swallow by John Sill

Rough-winged Swallow by John Sill. ©Massachusetts Audubon Society. Courtesy of the Museum of American Bird Art.

John Sill is a freelance wildlife artist living in the mountains of North Carolina. He was the illustrator for the Bird Identification Calendar for Mass Audubon for many years. His work has appeared in Birds In Art at the Leigh-Yawkey Woodson Art Museum, Wausau, Wisconsin, and in Art of the Animal Kingdom at the Bennington Center for the Arts in Vermont. He continues to illustrate the “About” and “About Habitats” series of natural history books for children written by his wife Cathryn.

Northern Rough-winged Swallow

The Northern Rough-winged Swallow (Stelgidopteryx serripennis) is something of a mystery bird because the adaptive significance of the rough wings that give the swallow its name remains a puzzle. The genus name combines two Greek words that mean “scraper-wing”, and the species name combines two Latin words that mean “saw-feather.” The stiff barbs of the outer edge of the outer primary feathers, which in the males are curved into hooklets and in females are pointed, are rough to the touch. The Northern Rough-winged Swallow is a small, brownish swallow with creamy white underparts. Its brownish back, flanks, and chest separate it from the adult Tree Swallow, and it lacks the distinct breast band of the smaller Bank Swallow. It feeds over water more consistently than other swallows and it often glides low over the surface and plunges its underside into the water prior to preening.

The taxonomy of the Rough-winged Swallow complex is complicated confusing, and in something of a muddle. In 1983, the Rough-winged Swallow (S. ruficollis), ranging from southern Canada to Argentina, was split into Northern (S. serripennis) and Southern (S. ruficollis) Rough-winged swallow species, the latter being distinguished by, among other characteristics, a lighter rump. The subspecies status of the Northern Rough-winged Swallow is still debated, with some taxonomists considering it monotypic (comprised of only one race) and others dividing it into five or six subspecies, with S. s. serripennis breeding in most of the United States and southern Canada except for the Southwest. Variation within populations makes subspecific designation even more problematic. To add to the confusion, some taxonomists consider two of the subspecies in Mexico and Central America to be full species.

The Northern Rough-winged Swallow breeds from southern Canada throughout most of the United States and winters in southern Florida, Mexico, and Central America. Year-round populations occur along the Gulf Coast, and in south Texas, Mexico, and Central America. The Northern Rough-winged Swallow was not reported in Massachusetts before the 1850s, but by 1925 it had a sparsely distributed breeding population. Today it is an uncommon, but widespread, breeder throughout the state. It is a common spring migrant but is rare in fall. It arrives in Massachusetts by mid-April and departs in late July or early August. In an interesting fall migration pattern, Northern Rough-winged Swallows congregate on the Gulf Coast, sometimes staying a month or more to complete their flight-feather molt, before making a trans-Gulf migration.

Northern Rough-winged Swallows are monogamous and produce a single brood per year. The song of the male is a buzzy series of rapid notes, variously described as brrt, jrrr, or jee. The male sings near the nest, and the song may function to some degree in mate-guarding. Also, a series of high notes may be given during territorial chases and fights, usually by the male. Females give a variety of alarm notes. During courtship and territorial disputes, the rough outer primary feathers produce a whistled or a whirring sound. In courtship, males may pursue females with the pair periodically alighting together. Courtship in the species is not well documented.

Northern Rough-winged Swallows nest singly or in small colonies ranging from two to 25 pairs, often at the edges of a Bank Swallow colony. They nest in a variety of hollows or burrows, including drainpipes and crevices; under bridges; in gravel pits; and in banks of sand or clay—in short, just about any vertical surface containing cavities or crevices. They frequently nest in the abandoned burrows of other birds, including Bank Swallows, kingfishers, and sometimes in the burrows of mammals. Local distribution is heavily dependent on nestsite availability. During nest construction both sexes are aggressive to intruders. They will swoop at interlopers, which may lead to fights with face-to-face hovering and sparring, which sometimes result in grasping with feet and bills and descent to the ground. When perched near the nest, adults may give a threat display, crouching with head forward and mouth open.

The female collects the nesting material from the ground and she alone builds the nest. The nest material is highly varied: twigs, grass, bark, moss, hair—anything that is available. The new nest may be built on the nest of the previous cavity user. The normal clutch is four to six white eggs, but clutch size is highly variable. Only the female develops a brood patch and she alone incubates the eggs for the 16 days until hatching. The chicks hatch helpless with eyes closed and they are covered in sparse down. The female broods the chicks for up to three weeks until they fledge; after the young fly from the nest, they seldom return. Both parents feed the chicks and continue to feed the young birds for several weeks after fledging. Eventually the young join flocks of adults to forage and roost.

Northern Rough-winged Swallows forage from dawn to dusk. They sweep low over the ground or water, hawking insects, which they sometimes take from the water surface. Their prey are almost exclusively flying insects. Sometimes they land to harvest particularly abundant prey, such as larvae feeding on dead fish. Primary insect prey includes flies, bees, and beetles.

Northern Rough-winged Swallow nests are depredated by snakes and many mammal species, including badgers, ground squirrels, and weasels. As early migrants, the swallows are subject to the vagaries of weather; young may starve if the weather is cold or rainy and flying insect populations are depressed. In some areas, only an estimated 10 % of returning migrants find suitable nest sites, and nest-site availability is doubtless a limiting factor in many populations. Breeding Bird Survey (BBS) data show varying periods of increase and decrease. Artificial burrows have proved successful, and the swallows’ use of man-made structures or road cuts for nesting is encouraging. The species is not listed as threatened anywhere within its range, and this bodes well for the future of Northern Rough-winged Swallows.

William E. Davis, Jr.

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