DescriptionThe 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 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. p1061–1064 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. p164–169 The song of the male barn swallow is a cheerful warble, often ending with ''su-seer'' with the second note higher than the first but falling in pitch. Calls include ''witt'' or ''witt-witt'' and a loud ''splee-plink'' when excited (or trying to chase intruders away from the nest). The This species is fairly quiet on the wintering grounds. The distinctive combination of a red face and blue breast band render the adult barn swallow easy to distinguish from the African ''Hirundo'' species and from the In Africa the short tail streamers of the juvenile barn swallow invite confusion with juvenile red-chested swallow (''Hirundo lucida''), but the latter has a narrower breast band and more white in the tail.
TaxonomyThe barn swallow was described by Carl Linnaeus in his 1758 10th edition of Systema Naturae, 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 and Antiquities of Selborne, 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 Taxonomy (biology), taxonomic problems within the genus, but the red-chested swallow—a resident of West Africa, the Congo River, 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 bird flight, flight, it looks paler underneath than barn swallow. p279
SubspeciesSix 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. * ''H. r. savignii'', the resident Egyptian subspecies, was described by James Francis Stephens, James Stephens in 1817 and named for French zoology, 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. Breast chestnut and 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 (state), 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 C. Jerdon, 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. p691 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. p343 Since the 1980s, small numbers of this subspecies have been found nesting in Argentina. The short wings, red belly and incomplete breast band of ''H. r. tytleri'' are also found in ''H. r. erythrogaster'', and DNA analyses show that barn swallows from North America colonised the Lake Baikal, Baikal region of Siberia, a dispersal direction opposite to that for most changes in distribution between North America and Eurasia.
Habitat and rangeThe 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. It breeds in the Northern Hemisphere from sea level to typically , 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 Common house martin, house martin. However, in Honshū, Japan, the barn swallow is a more urban bird, with the red-rumped swallow (''Cecropis daurica'') replacing it as the rural species. In winter, the barn swallow is cosmopolitan in its choice of habitat, avoiding only dense forests and deserts. p294 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. p315–6 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 communal roosting, 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 hobby, 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. p234 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.
FeedingThe barn swallow is similar in its habits to other aerial insectivores, including other swallow species and the unrelated Swift (bird), swifts. It is not a particularly fast flier, with a speed estimated at about , 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 fly, 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 Common house martin, house or sand martins. On the wintering grounds, Hymenoptera, especially flying ants, are important food items. When egg-laying barn swallows hunt in pairs, but otherwise will form often Group size measures, large flocks. The amount of food a clutch will get depends on the size of the clutch, with larger clutches getting more food on average. The timing of a clutch also determines the food given; later broods get food that is smaller in size compared to earlier broods. This is because larger insects are too far away from the nest to be profitable in terms of energy expenditure. Isotope studies have shown that wintering populations may utilise different feeding habitats, with British breeders feeding mostly over grassland, whereas Switzerland, 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. This bird bathes in a similar fashion, dipping into the water for an instant while in flight. 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. p242 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.
BreedingThe male barn swallow returns to the breeding grounds before the females and selects a nest site, which is then advertised to females with a circling flight and song. Plumage may be used to advertise: in some populations, like in the subspecies ''H. r. gutturalis'', darker ventral plumage in males is associated with higher breeding success. In other populations, 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. Males in northern Europe have longer tails than those further south; whereas in Spain the male's tail streamers are only 5% longer than the female's, in Finland the difference is 20%. In Denmark, the average male tail length increased by 9% between 1984 and 2004, but it is possible that climatic changes may lead in the future to shorter tails if summers become hot and dry. Males with long streamers also have larger white tail spots, and since feather-eating chewing louse, bird lice prefer white feathers, large white tail spots without Parasitism, parasite damage again demonstrate breeding quality; there is a positive association between spot size and the number of offspring produced each season. 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. Once established, pairs stay together to breed for life, but extra-pair Mating, copulation is common, making this species genetically polygamy, polygamous, despite being socially monogamy, monogamous. 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. Before man-made sites became common, it nested on cliff faces or in caves, but this is now rare. The neat cup-shaped nest is placed on a beam or against a suitable vertical projection. It is constructed by both sexes, although more often by the female, with mud pellets collected in their beaks and lined with grasses, feathers, algae or other soft materials. The nest building ability of the male is also sexually selected; females will lay more eggs and at an earlier date with males who are better at nest construction, with the opposite being true with males that are not. 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. Group size measures, Colony size tends to be larger in North America. In North America at least, barn swallows frequently engage in a Mutualism (biology), mutualist relationship with ospreys. Barn swallows will build their nest below an osprey nest, receiving protection from other birds of prey that are repelled by the exclusively fish-eating ospreys. The ospreys are alerted to the presence of these predators by the alarm calls of the swallows. There are normally two broods, with the original nest being reused for the second brood and being repaired and reused in subsequent years. The female lays two to seven, but typically four or five, reddish-spotted white eggs. The clutch size is influenced by latitude, with clutch sizes of northern populations being higher on average than southern populations. The eggs are in size, and weigh , of which 5% is shell. In Europe, the female does almost all the avian incubation, 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. Compared to those from early broods, juvenile barn swallows from late broods have been found to migrate at a younger age, fuel less efficiently during migration and have lower return rates the following year. The barn swallow will mobbing behavior, 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 parasite, Brood parasitism by cowbirds in North America or cuckoos in Eurasia is rare. Hatching success is 90% and the fledging survival rate is 70–90%. Average mortality is 70–80% in the first year and 40–70% for the adult. Although the record age is more than 11 years, most survive less than four years. Barn swallow nestlings have prominent red gapes, a feature shown to induce feeding by parent birds. An experiment in manipulating brood size and immune system showed the vividness of the gape was positively correlated with T-cell–mediated immunocompetence, and that larger brood size and injection with an antigen led to a less vivid gape. The barn swallow has been recorded as hybrid (biology), hybridising with the American cliff swallow, 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.
Parasites and predatorsBarn swallows (and other small passerines) often have characteristic feather holes on their wing and tail feathers. These holes were suggested as being caused by Phthiraptera, avian lice such as ''Machaerilaemus malleus'' and ''Myrsidea rustica'', although other studies suggest that they are mainly caused by species of ''Brueelia''. Several other species of lice have been described from barn swallow hosts, including ''Brueelia domestica'' and ''Philopterus microsomaticus''. 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.
StatusThe barn swallow has an enormous range, with an estimated global extent of and a population of 190 million individuals. The species is evaluated as least concern on the 2007 IUCN Red List, and has no special status under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which regulates international trade in specimens of wild animals and plants. 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. A specific threat to wintering birds from the European populations is the transformation by the South African government of a light aircraft runway near Durban into King Shaka International Airport, an international airport for the 2010 FIFA World Cup. The roughly square Mount Moreland reed bed is a night roost for more than three million barn swallows, which represent 1% of the global population and 8% of the European breeding population. The reed bed lies on the flight path of aircraft using the proposed La Mercy airport, and there were fears that it would be cleared because the birds could threaten aircraft safety. 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 humansThe 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. In the Old World, the barn swallow appears to have used man-made structures and bridges since time immemorial. An early reference is in Virgil's ''Georgics'' (29 BC), "''Ante garrula quam tignis nidum suspendat hirundo''" (Before the twittering swallow hangs its nest from the rafters). Virgil, ''The Georgics'
In literatureMany 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 ''"Quando fiam uti chelidon [ut tacere desinam]?"'' ("When will I be like the swallow, so that I can stop being silent?") This refers to the myth of Philomela (princess of Athens), Philomela in which she turns into a nightingale, and her sister Procne into a . On the other hand, an image of the assembly of swallows for their southward migration concludes John Keats's ode "To Autumn". The swallow is cited in several of William Shakespeare's plays for the swiftness of its flight, with "True hope is swift, and flies with swallow's wings" from Act 5 of ''Richard III (play), Richard III'', and "I have horse will follow where the game Makes way, and run like swallows o'er the plain." from the second act of ''Titus Andronicus''. Shakespeare references the annual migration of the species in ''The Winter's Tale'', Act 4: "Daffodils, That come before the swallow dares, and take The winds of March with beauty". A swallow is the main character in Oscar Wilde's story, The Happy Prince and Other Tales, The Happy Prince.
In cultureGilbert 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. Elsewhere, its long journeys have been well observed, and a swallow tattoo is popular amongst nautical men as a symbol of a safe return; the tradition was that a mariner had a tattoo of this fellow wanderer after sailing . A second swallow would be added after at sea. 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. It is depicted as the ''martlet'', ''merlette'' or ''merlot'' in heraldry, where it represents younger sons who have no lands. It is also represented as lacking feet as this was a common belief at the time. As a result of a campaign by ornithology, ornithologists, the barn swallow has been the national bird of since 23 June 1960.
Barn swallows on postage stampsBarn swallows are one of the most depicted birds on stamps, birds on postage stamps around the world.
See also* Bird migration#Swallow migration versus hibernation, Swallow migration versus hibernation