Barn swallow

Name and taxonomy

Carl Linnaeus named the bird Hirundo rustica in 1758. Hirundo is simply the Latin for swallow. The word rusticus means of the countryside. The Oxford English Dictionary traces the English name barn swallow to 1851. Gilbert White used it earlier, in 1789, and noted the Swedish word ladusvala. The English name may therefore be a straight translation of the Swedish one.

In Britain and Ireland people call the bird simply the swallow. Across northern Europe, only this species of its family carries the word swallow, and the rest are martins. The genus Hirundo is mostly African, and this is the only species of it that reaches the Americas. The red-chested swallow of West Africa was once counted as a subspecies. It is now a species of its own, smaller and with a narrower breast band.

Evolution and relatives

The barn swallow belongs to the Hirundinidae, the swallows and martins. Swifts hunt in the same way and look similar, but they are not close relatives. Eight subspecies are generally recognised, and all of them breed north of the equator. Two have small ranges: one in the Nile valley and one in the eastern Mediterranean. The Egyptian race is the only one that stays put all year.

The North American race has redder underparts and a narrow, often broken, breast band. The Siberian race shares that pattern of short wings and a red belly. DNA shows that American birds colonised the Baikal region, not the other way round. That direction is the reverse of most range changes between the two continents. The bird hybridises with the cliff swallow, the cave swallow and the house martin. The cross with the house martin is one of the commonest hybrids among songbirds.

Appearance

The upperparts are glossy steel blue. A red forehead, chin and throat sit above a broad dark blue band across the chest. Below that band the underparts are off-white or cream. A row of white spots crosses the outer tail near its base. A male is 17 to 19 cm long, and the streamers account for 2 to 7 cm of it. The wingspan runs from 32 to 34.5 cm and the weight from 16 to 22 g.

The female looks much like the male, with shorter streamers and duller blue. Her underparts are paler than his. The gap between the sexes changes with latitude. In Spain a male's streamers beat a female's by only 5%, but in Finland the gap is 20%. A juvenile is browner, with a pale red face, whiter underparts and no streamers at all. The red face with the blue chest band separates the adult from every African swallow.

Habitat and range

The barn swallow wants open country with short vegetation and water nearby. Pasture, hay meadows and farmland suit it best. It keeps away from thick woodland, steep ground and dense city centres. It needs an open building for the nest and a wire or bare branch for a perch. It breeds from sea level to 2,700 metres, and to 3,000 m in the Caucasus and North America. Only the deserts and the far cold north lie outside the breeding range.

In winter the bird accepts almost any open country. Savanna and ranch land hold large numbers. In Venezuela, South Africa and Trinidad it favours burnt or cut sugarcane fields. Wintering birds return to the same district year after year. They gather at dusk in reed beds, and a roost in Nigeria was estimated at 1.5 million birds. GBIF holds occurrence records from 227 countries and territories.

Ringing proved the migration in 1912, when a bird from Staffordshire turned up in Natal. Swallows wintering in southern Africa come from right across Eurasia. One journey was measured at up to 11,660 kilometres. Vagrants have reached Hawaii, Bermuda, Greenland, the Falkland Islands and Antarctica. A few birds now breed in the warmer parts of the winter range, such as central Argentina.

Diet and feeding

Flying insects make up about 99% of the diet. Large flies account for roughly 70% of what breeding birds eat, and aphids matter too. Flying ants and other Hymenoptera take over on the wintering grounds. Grasshoppers, crickets, dragonflies, beetles and moths are all caught. The bird hunts about 7 to 8 metres above open ground or shallow water. It sometimes plucks prey off the water, a wall or a leaf instead.

Barn swallows follow cattle, people and farm machinery to snap up disturbed insects. They have been watched hunting the flies around an occupied stork nest. Birds hunt in pairs while the female is laying and in flocks the rest of the time. British breeders feed mostly over grassland, while Swiss birds use woodland more. A study in West Virginia found birds foraging within 1.2 kilometres of the nest. In Europe they stayed within about 500 metres of it.

The bird drinks on the wing, skimming a lake or river with its mouth open. It bathes the same way, dipping into the water for an instant as it passes. Parents carry food to the nest as a pellet held in the throat. They may bring food to the chicks up to 400 times in a day. A large brood gets more food than a small one. Late broods get smaller insects, because the big ones are too far from the nest to be worth the flight.

Behaviour and social life

The barn swallow is active by day and migrates by day as well. It is not a fast flier by the standards of the air. The usual speed is about 40 kilometres per hour, and the top speed is about 72 km/h. The wings beat about five times a second, and up to nine when the bird works hard. Birds rest in rows on telephone wires and roof ridges between flights.

Pairs are semi-colonial and settle in groups of one to a few dozen. Large wooden buildings that hold livestock draw the biggest groups. Each pair guards a small patch around its nest, 4 to 8 square metres in Europe. Colonies in North America tend to be larger than European ones. The same birds often come back to the same building year after year. Experiments show they choose the site for its free nests rather than for the neighbours.

After breeding, the birds gather in communal roosts of thousands. Reed beds are the favourite, and the flock swirls above them before dropping in. The reeds also hold the insects that let a bird lay down fat before a long flight. Arrivals at a roost are timed together, which probably swamps the waiting falcons. In North America the swallows often nest under an osprey nest. The osprey eats only fish and drives off hawks, while the swallows call the alarm for it.

Communication and senses

Males sing to hold a small territory and to attract a mate. The song runs from late April into August across much of the range. It opens with a twittering warble and rises into a syllable of its own. A short note and a trilled rattle of pulses close the phrase. Some populations add a final note after the rattle.

Female song was described only recently. It is much shorter than the male's and comes early in the breeding season. Females sing on their own account and answer each other. The common call is a witt or a doubled witt-witt. An excited bird chasing an intruder gives a loud splee-plink.

The alarm calls name the danger. A sharp siflitt warns of a cat, and a flitt-flitt warns of a hobby or other raptor. Nestlings give a faint chirp as they beg. Adults also snap the bill to make a clicking noise. A nestling's gape is bright red, and that colour makes the parents feed it. A duller gape goes with a weaker immune system, so the colour reports the chick's health.

Reproduction and life cycle

The male arrives on the breeding ground first and picks a nest site. He advertises it to females by circling the spot and singing. Females favour males with the longest tail streamers. Long-tailed males live longer and resist disease better, so the choice pays off in the chicks. Long streamers come with larger white tail spots, which feather lice attack first. Clean white spots therefore prove that a male carries few parasites.

Pairs stay together for life, but both sexes mate outside the pair. The male guards his mate closely and may give a false alarm call to break up a rival's attempt. Both birds build the nest, though the female does most of it. They carry mud pellets in the bill and line the cup with grass, feathers or algae. Building takes about two weeks, so an old nest is worth a great deal. Females lay earlier and lay more eggs for a male that builds well.

A clutch holds two to seven white eggs with reddish spots, and four or five is usual. Northern birds lay larger clutches than southern ones. An egg measures about 20 by 14 millimetres and weighs about 1.9 grams. Incubation lasts 14 to 19 days, and the chicks fly 18 to 23 days after hatching. European females do nearly all the sitting, while North American males may take a quarter of it. Parents feed the fledged young for about a week more. Most pairs raise two broods, and chicks from the first sometimes help feed the second.

About 90% of eggs hatch, and 70 to 90% of the chicks reach flight. Then the losses begin: 70 to 80% of young birds die in their first year. Adults lose 40 to 70% of their number each year. Most birds live about 4 years, and a bird of 8 years is exceptional. AnAge records a maximum of 16 years. Young birds can breed in the summer after they hatch, though they lay fewer eggs than older ones.

Predators and threats

Falcons take adults, and the peregrine and the African hobby both hunt at the roosts. Hawks such as the sparrowhawk and Cooper's hawk take birds on the wing. Owls, gulls and grackles also kill them. Rats, squirrels, weasels, raccoons, cats and snakes mostly reach the nestlings. In Africa the tigerfish leaps clear of the water to seize a swallow flying low. Adults escape by flying fast and turning sharply, and they mob a cat or a hawk near the nest.

Feather lice chew holes in the wing and tail feathers. They prefer the white tail spots, and short-tailed males carry the most of them. Brood parasites are rare, though cowbirds in America and cuckoos in Eurasia sometimes try. The heavier threats come from farming. Where farms close, insect numbers fall by about half, and the swallows go with them. DDT cut numbers in Israel in the 1950s, and house sparrows took American nest sites in the 19th century.

Population and conservation

About 190 million barn swallows live across a range of roughly 250 million square kilometres. The IUCN Red List placed the species in Least Concern in 2019. CITES gives it no special status. iNaturalist holds 240,697 observations of the bird. Forest clearance and farm buildings helped the species for centuries.

Numbers are now easing downwards in parts of Europe and Asia. Intensive farming leaves fewer insects for the chicks. North American numbers rose through the 20th century as nest sites multiplied. The birds moved north into Alberta as they spread. A reed bed at Mount Moreland near Durban holds over three million wintering swallows. That is 1% of the world population and 8% of the European breeding birds.

An airport built for the 2010 football World Cup put that roost at risk. Aircraft use a flight path over the reeds, which are about 250 metres across. Radar now tracks the flocks and warns the pilots instead. A warming climate cuts both ways for the species. Drought slows feather growth, and a wider Sahara makes the crossing harder. Warmer springs may stretch the breeding season and yield more chicks.

Relationship with humans

Few wild birds live as close to people as this one. Before barns existed it nested on cliffs and in caves, which is now rare. Today almost every nest sits inside a building or under a bridge or wharf. Farmers have long tolerated it because it clears flies from the yard. Virgil wrote of the swallow hanging its nest from the rafters in 29 BC.

Not everyone welcomes it. The nests are messy, and a large colony on a building creates a cleaning problem. Cattle farmers once believed that swallows spread salmonella through their droppings. A Swedish study found no sign that the birds carry the bacterium. The bird also warns of trouble, because its numbers fall before other signs of harm appear.

Nest sites pass down the years when nobody disturbs them. A nest that is patched each spring lasts 10 to 15 years without trouble. One nest was reported in use for 48 years. British birdwatchers still greet the first swallow as the opening of summer. The bird is on the UK Green List, which marks a species of least concern there.

In culture and myth

The swallow stands for spring in European writing. Aristotle wrote in the Nicomachean Ethics that one swallow does not make a spring. The saying survives as a warning against a single piece of evidence. The late Latin poem Pervigilium Veneris ties the bird to spring and to love. T. S. Eliot quoted a line of it in The Waste Land. In Greek myth Procne became a swallow while her sister Philomela became a nightingale.

In European folk belief, harming a swallow's nest brought loss to the farm. Cows would give bloody milk or none, and hens would stop laying. That fear probably explains why so many old nests survive on beams. In heraldry the swallow appears as the martlet, drawn without feet. The martlet marks a younger son, who inherits no land.

In sailors' tradition a swallow tattoo marked distance covered at sea. One account awards the first swallow at 5,000 nautical miles, and the second at 10,000. The two birds sat one on each side of the chest. The custom may be more recent than sailors claim, since old records show no such designs. Estonia adopted the barn swallow as its national bird in 1960, and Austria has done the same.