The barn swallow (Hirundo rustica) 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 eight subspecies of barn swallow, which breed across the Northern Hemisphere. Two subspecies (H. r. savignii and H. r. transitiva) have fairly restricted ranges in the Nile valley and eastern Mediterranean, respectively.

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

thumb|Reported range from observations submitted to [[eBird shows the migration pattern of the species|alt=See caption]]

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. (See below for details about song.) Calls include witt or witt-witt and a loud splee-plink when excited or trying to chase intruders away from the nest. 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". 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:

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The swallow, though called the chimney-swallow, by no means builds altogether in chimnies , but often within barns and out-houses against the rafters&nbsp;... In Sweden she builds in barns, and is called ladusvala, the barn-swallow.

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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 (in the adult) has shorter tail streamers. In flight, it looks paler underneath than barn swallow.

Subspecies

thumb|Holotype of Chelidon rustica transitiva Hartert (NML-VZ T2057) held at World Museum, National Museums Liverpool|alt=See caption

thumb|A European barn swallow pauses to rest on a fence post beside a freshwater lake on [[Lindisfarne.]]

Eight subspecies of barn swallow are generally recognised. In eastern Asia, a number of additional or alternative forms have been proposed, including H.&nbsp;r. kamtschatica by Benedykt Dybowski in 1883 Given the uncertainties over the validity of these forms, this article follows the IOC World Bird List and AviList. 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 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 after the French zoologist Marie Jules César Savigny. It resembles H.&nbsp;r. transitiva, which also has orange-red underparts, but H.&nbsp;r. savignii has a complete broad breast band and deeper red hue on the underparts; unlike the other subspecies it is non-migratory. 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.&nbsp;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. but is easily distinguished from the North American breeding subspecies, H.&nbsp;r. erythrogaster, by the latter's reddish underparts. 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 about 1980, small but increasing 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. Because it takes around 2 weeks for a pair to build a nest from mud, hair, and other materials, old nests are highly prized.

thumb|right|H. r. rustica juveniles|alt=A group of juvenile swallow resting in a tree.

thumb|The movement of two swallows in slow motion|alt=See caption

This species breeds across the Northern Hemisphere from sea level to , but to in the Caucasus 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

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,

Feeding

thumb|Chicks in the nest|alt=Three chicks in a nest with their beaks open.

The barn swallow is similar in its habits to other aerial insectivores, including other swallow species and the unrelated swifts. It is not a particularly fast flier, with a speed estimated at , up to and a wing beat rate of approximately 5, up to 7–9 times each second.

The barn swallow typically feeds in open areas above shallow water or the ground often following animals, humans or farm machinery to catch disturbed insects, but it will occasionally pick prey items from the water surface, walls and plants. In the breeding areas, large flies make up around 70% of the diet, with aphids also a significant component. However, in Europe, the barn swallow consumes fewer aphids than the house or sand martins. When egg-laying, barn swallows hunt in pairs, but otherwise will form often large flocks.

Isotope studies have shown that wintering populations may utilise different feeding habitats, with British breeders feeding mostly over grassland, whereas Swiss birds utilised woodland more. Another study showed that a single population breeding in Denmark actually wintered in two separate areas.

The barn swallow drinks by skimming low over lakes or rivers and scooping up water with its open mouth.

Swallows gather in communal roosts after breeding, sometimes thousands strong. Reed beds are regularly favoured, with the birds swirling en masse before swooping low over the reeds. Reed beds are an important source of food prior to and whilst on migration; although the barn swallow is a diurnal migrant that can feed on the wing whilst it travels low over ground or water, the reed beds enable fat deposits to be established or replenished.

Song

Males sing to defend small territories (when living in colonies, less so in solitary pairs) and to attract mates. Males sing throughout the breeding season, from late April into August in many parts of the range. Their song is made up of a "twitter warble," followed by a rising "P-syllable" in European H.&nbsp;r. rustica and the North American H.&nbsp;r. erythrogaster. In all subspecies, this is followed by a short "Q-syllable" and a trilled series of pulses, termed the "rattle." The rattle is sometimes followed by a terminal "Ω-Note" in some subspecies' populations, and always at the end of H.&nbsp;r. tytleri song. the breeding success of the male is related to the length of the tail streamers, with longer streamers being more attractive to the female. Males with longer tail feathers are generally longer-lived and more disease resistant, females thus gaining an indirect fitness benefit from this form of selection, since longer tail feathers indicate a genetically stronger individual which will produce offspring with enhanced vitality.

The breeding season of the barn swallow is variable: in the southern part of the range, the breeding season usually is from February or March to early to mid September, although some late second and third broods finish in October. In the northern part of the range, it usually starts late May to early June and ends the same time as the breeding season of the southernmost birds.

Both sexes defend the nest, but the male is particularly aggressive and territorial. Males guard females actively to avoid being cuckolded. Males may use deceptive alarm calls to disrupt extrapair copulation attempts toward their mates.

As its name implies, the barn swallow typically nests inside accessible buildings such as barns and stables, or under bridges and wharves. or other soft materials. After building the nest, barn swallows may nest colonially where sufficient high-quality nest sites are available, and within a colony, each pair defends a territory around the nest which, for the European subspecies, is in size. Colony size tends to be larger in North America. The eggs are in size, and weigh , of which 5% is shell. In Europe, the female does almost all the incubation, but in North America the male may incubate up to 25% of the time. The incubation period is normally 14–19 days, with another 18–23 days before the altricial chicks fledge. The fledged young stay with, and are fed by, the parents for about a week after leaving the nest. Occasionally, first-year birds from the first brood will assist in feeding the second brood.

Juvenile being fed|thumb|left|alt=A swallow is feeding an insect to another swallow

The barn swallow will mob intruders such as cats or accipiters that venture too close to their nest, often flying very close to the threat. Adult barn swallows have few predators, but some are taken by accipiters, falcons, and owls. Brood parasitism by cowbirds in North America or cuckoos in Eurasia is rare.

The barn swallow has been recorded as hybridising with the cliff swallow (Petrochelidon pyrrhonota) and the cave swallow (P. fulva) in North America, and the house martin (Delichon urbicum) in Eurasia, the cross with the latter being one of the most common passerine hybrids. The avian lice prefer to feed on white tail spots, and they are generally found more numerously on short-tailed males, indicating the function of unbroken white tail spots as a measure of quality. In Texas, the swallow bug (Oeciacus vicarius), which is common on species such as the cliff swallow, is also known to infest barn swallows.

Predatory bats such as the greater false vampire bat are known to prey on barn swallows. Swallows at their communal roosts attract predators and several falcon species make use of these opportunities. Falcon species confirmed as predators include the peregrine falcon and the African hobby. In Africa, tigerfish Hydrocynus vittatus have been recorded to routinely leap out of the water to capture low-flying swallows.

Status

thumb|Barn swallow at the moment when its beak touches the water to have a drink in Bagmati River, Nepal|alt=See caption

thumb|A reflection flight of barn swallow|alt=See caption

The barn swallow has an enormous range, with an estimated global extent of about and a population of 190 million individuals. The species is evaluated as least concern on the 2019 IUCN Red List,

This is a species that has greatly benefited historically from forest clearance, which has created the open habitats it prefers, and from human habitation, which have given it an abundance of safe man-made nest sites. There have been local declines due to the use of DDT in Israel in the 1950s, competition for nest sites with house sparrows in the US in the 19th century, and an ongoing gradual decline in numbers in parts of Europe and Asia due to agricultural intensification, reducing the availability of insect food. However, there has been an increase in the population in North America during the 20th century with the greater availability of nesting sites and subsequent range expansion, including the colonisation of northern Alberta. However, following detailed evaluation, advanced radar technology will be installed to enable planes using the airport to be warned of bird movements and, if necessary, take appropriate measures to avoid the flocks.

Climate change may affect the barn swallow; drought causes weight loss and slow feather regrowth, and the expansion of the Sahara will make it a more formidable obstacle for migrating European birds. Hot dry summers will reduce the availability of insect food for chicks. Conversely, warmer springs may lengthen the breeding season and result in more chicks, and the opportunity to use nest sites outside buildings in the north of the range might also lead to more offspring.

Relationship with humans

The barn swallow is an attractive bird that feeds on flying insects and has therefore been tolerated by humans when it shares their buildings for nesting. As one of the earlier migrants, this conspicuous species is also seen as an early sign of summer's approach.

Many cattle farmers believed that swallows spread Salmonella infections; however, a study in Sweden showed no evidence of the birds being reservoirs of the bacteria.

In literature

Many literary references are based on the barn swallow's northward migration as a symbol of spring or summer. The proverb about the necessity for more than one piece of evidence goes back at least to Aristotle's Nicomachean Ethics: "For as one swallow or one day does not make a spring, so one day or a short time does not make a fortunate or happy man."

The barn swallow symbolises the coming of spring and thus love in the Pervigilium Veneris, a late Latin poem. In his poem "The Waste Land", T. S. Eliot quoted the line ("When will I be like the swallow, so that I can stop being silent?") This refers to the myth of Philomela in which she turns into a nightingale, and her sister Procne into a swallow.

In culture

Gilbert White studied the barn swallow in detail in his pioneering work The Natural History of Selborne, but even this careful observer was uncertain whether it migrated or hibernated in winter.

In the past, the tolerance for this beneficial insectivore was reinforced by superstitions regarding damage to the barn swallow's nest. Such an act might lead to cows giving bloody milk, or no milk at all, or to hens ceasing to lay. This may be a factor in the longevity of swallows' nests. Survival, with suitable annual refurbishment, for 10–15 years is regular, and one nest was reported to have been occupied for 48 years. As a result of a campaign by ornithologists, the barn swallow has been the national bird of Estonia since 23 June 1960, and is also the national bird of Austria.

See also

  • Swallow migration versus hibernation

References

Further reading

  • European Swallow (barn swallow) – Species text in The Atlas of Southern African Birds.
  • Barn swallow - Hirundo rustica – USGS Patuxent Bird Identification InfoCenter
  • Barn Swallow Species Account – Cornell Lab of Ornithology
  • BirdLife species' status map for Europe (pdf).
  • Ageing and sexing (PDF; 2.3 MB) by Javier Blasco-Zumeta & Gerd-Michael Heinze
  • Feathers of barn swallow (Hirundo rustica)
  • Barn swallow Structured guide to the species in southern Africa