Barn swallow
The barn swallow is the most widespread species of swallow in the world, occurring on all continents, with vagrants reported even in Antarctica. It is a distinctive passerine bird with blue upperparts and a long, deeply forked tail. In Anglophone Europe, it is just called the swallow; in northern Europe, it is the only member of family Hirundinidae called a "swallow" rather than a "martin".
There are six subspecies of barn swallow, which breed across the Northern Hemisphere. Two subspecies have fairly restricted ranges in the Nile valley and eastern Mediterranean, respectively. The other four are more widespread, with winter ranges covering much of the Southern Hemisphere.
The barn swallow is a bird of open country that normally nests in man-made structures and consequently has spread with human expansion. It builds a cup nest from mud pellets in barns or similar structures and feeds on insects caught in flight. This species lives in close association with humans, and its insect-eating habits mean that it is tolerated by humans; this acceptance was reinforced in the past by superstitions regarding the bird and its nest. There are frequent cultural references to the barn swallow in literary and religious works due to both its living in close proximity to humans and its annual migration. The barn swallow is the national bird of Austria and Estonia.
Description
The adult male barn swallow of the nominate subspecies H. r. rustica is long including of elongated outer tail feathers. It has a wingspan of and weighs. It has steel blue upperparts and a rufous forehead, chin and throat, which are separated from the off-white underparts by a broad dark blue breast band. The outer tail feathers are elongated, giving the distinctive deeply forked "swallow tail". There is a line of white spots across the outer end of the upper tail. The female is similar in appearance to the male, but the tail streamers are shorter, the blue of the upperparts and breast band is less glossy, and the underparts paler. The juvenile is browner and has a paler rufous face and whiter underparts. It also lacks the long tail streamers of the adult.Although both sexes sing, female song was only recently described. Calls include witt or witt-witt and a loud splee-plink when excited or trying to chase intruders away from the nest. The alarm calls include a sharp siflitt for predators like cats and a flitt-flitt for birds of prey like the hobby. This species is fairly quiet on the wintering grounds.
The distinctive combination of a red face and blue breast band renders the adult barn swallow easy to distinguish from the African Hirundo species and from the welcome swallow with which its range overlaps in Australasia. In Africa the short tail streamers of the juvenile barn swallow invite confusion with juvenile red-chested swallow, but the latter has a narrower breast band and more white in the tail.
Taxonomy
The barn swallow was described by Carl Linnaeus in his 1758 10th edition of Systema Naturae as Hirundo rustica, characterised as "H. rectricibus, exceptis duabus intermediis, macula alba notatîs". Hirundo is the Latin word for "swallow"; rusticus means "of the country". This species is the only one of that genus to have a range extending into the Americas, with the majority of Hirundo species being native to Africa. This genus of blue-backed swallows is sometimes called the "barn swallows".The Oxford English Dictionary dates the English common name "barn swallow" to 1851, though an earlier instance of the collocation in an English-language context is in Gilbert White's popular book The Natural History of Selborne, originally published in 1789:
The swallow, though called the chimney-swallow, by no means builds altogether in chimnies, but often within barns and out-houses against the rafters ... In Sweden she builds in barns, and is called ladusvala, the barn-swallow.
This suggests that the English name may be a calque on the Swedish term.
There are few taxonomic problems within the genus, but the red-chested swallow—a resident of West Africa, the Congo Basin, and Ethiopia—was formerly treated as a subspecies of barn swallow. The red-chested swallow is slightly smaller than its migratory relative, has a narrower blue breast-band, and has shorter tail streamers. In flight, it looks paler underneath than barn swallow.
Subspecies
Six subspecies of barn swallow are generally recognised. In eastern Asia, a number of additional or alternative forms have been proposed, including saturata by Robert Ridgway in 1883, kamtschatica by Benedykt Dybowski in 1883, ambigua by Erwin Stresemann and mandschurica by Wilhelm Meise in 1934. Given the uncertainties over the validity of these forms, this article follows the treatment of Turner and Rose.- H. r. rustica, the nominate European subspecies, breeds in Europe and Asia, as far north as the Arctic Circle, south to North Africa, the Middle East and Sikkim, and east to the Yenisei River. It migrates on a broad front to winter in Africa, Arabia, and the Indian subcontinent. The barn swallows wintering in southern Africa are from across Eurasia to at least 91°E, and have been recorded as covering up to on their annual migration. The nominate European subspecies was the first to have its genome sequenced and published.
- H. r. transitiva was described by Ernst Hartert in 1910. It breeds in the Middle East from southern Turkey to Israel and is partially resident, though some birds winter in East Africa. It has orange-red underparts and a broken breast band. The holotype of Chelidon rustica transitiva Hartert, an adult female, is held in the vertebrate zoology collection of National Museums Liverpool at World Museum, with accession number NML-VZ T2057. The specimen was collected in the Plains of Esdraclon, Palestine on 16 December 1863 by Henry Baker Tristram. The specimen came to the Liverpool national collection through the purchase of Canon Henry Baker Tristram's collection by the museum in 1896.
- H. r. savignii, the resident Egyptian subspecies, was described by James Stephens in 1817 and named for French zoologist Marie Jules César Savigny. It resembles transitiva, which also has orange-red underparts, but savignii has a complete broad breast band and deeper red hue to the underparts.
- H. r. gutturalis, described by Giovanni Antonio Scopoli in 1786, has whitish underparts and a broken breast band. The breast is chestnut and the lower underparts more pink-buff. The populations that breed in the central and eastern Himalayas have been included in this subspecies, although the primary breeding range is Japan and Korea. The east Asian breeders winter across tropical Asia from India and Sri Lanka east to Indonesia and New Guinea. Increasing numbers are wintering in Australia. It hybridises with H. r. tytleri in the Amur River area. It is thought that the two eastern Asia forms were once geographically separate, but the nest sites provided by expanding human habitation allowed the ranges to overlap. H. r. gutturalis is a vagrant to Alaska and Washington, but is easily distinguished from the North American breeding subspecies, H. r. erythrogaster, by the latter's reddish underparts.
- H. r. tytleri, first described by Thomas Jerdon in 1864, and named for British soldier, naturalist and photographer Robert Christopher Tytler, has deep orange-red underparts and an incomplete breast band. The tail is also longer. It breeds in central Siberia south to northern Mongolia and winters from eastern Bengal east to Thailand and Malaysia.
- H. r. erythrogaster, the North American subspecies described by Pieter Boddaert in 1783, differs from the European subspecies in having redder underparts and a narrower, often incomplete, blue breast band. It breeds throughout North America, from Alaska to southern Mexico, and migrates to the Lesser Antilles, Costa Rica, Panama and South America to winter. A few may winter in the southernmost parts of the breeding range. This subspecies funnels through Central America on a narrow front and is therefore abundant on passage in the lowlands of both coasts. Since the 1980s, small numbers of this subspecies have been found nesting in Argentina.
Behaviour
Habitat and range
The preferred habitat of the barn swallow is open country with low vegetation, such as pasture, meadows and farmland, preferably with nearby water. This swallow avoids heavily wooded or precipitous areas and densely built-up locations. The presence of accessible open structures such as barns, stables, or culverts to provide nesting sites, and exposed locations such as wires, roof ridges or bare branches for perching, are also important in the bird's selection of its breeding range.Barn swallows are semi-colonial, settling in groups from a single pair to a few dozen pairs, particularly in larger wooden structures housing animals. The same individuals often breed at the same site year after year, although settlement choices have been experimentally shown to be predicted by nest availability rather than any characteristics of available mates. Because it takes around 2 weeks for a pair to build a nest from mud, hair, and other materials, old nests are highly prized.
This species breeds across the Northern Hemisphere from sea level to, but to in the Caucasus and North America, and it is absent only from deserts and the cold northernmost parts of the continents. Over much of its range, it avoids towns, and in Europe is replaced in urban areas by the house martin. However, in Honshū, Japan, the barn swallow is a more urban bird, with the red-rumped swallow replacing it as the rural species.
In winter, the barn swallow is cosmopolitan in its choice of habitat, avoiding only dense forests and deserts. It is most common in open, low vegetation habitats, such as savanna and ranch land, and in Venezuela, South Africa and Trinidad and Tobago it is described as being particularly attracted to burnt or harvested sugarcane fields and the waste from the cane. In the absence of suitable roost sites, they may sometimes roost on wires where they are more exposed to predators. Individual birds tend to return to the same wintering locality each year and congregate from a large area to roost in reed beds. These roosts can be extremely large; one in Nigeria had an estimated 1.5 million birds. These roosts are thought to be a protection from predators, and the arrival of roosting birds is synchronised in order to overwhelm predators like African hobbies. The barn swallow has been recorded as breeding in the more temperate parts of its winter range, such as the mountains of Thailand and in central Argentina.
Migration of barn swallows between Britain and South Africa was first established on 23 December 1912 when a bird that had been ringed by James Masefield at a nest in Staffordshire, was found in Natal. As would be expected for a long-distance migrant, this bird has occurred as a vagrant to such distant areas as Hawaii, Bermuda, Greenland, Tristan da Cunha, the Falkland Islands, and even Antarctica.