Barn swallows are small birds. They are 14.6 to 19.9 cm long and have a wingspan of 31.8 to 34.3 cm. They weigh between 17 and 20 g. Barn swallows are metallic blue-black above and pale beige below. They have light brown on their throat and forehead, and have a long, deeply-forked tail. Males and females look very similar. However, females tend to be less brightly colored and have shorter tails. (Moller, 1994a; Moller, 1994b; Terres, 1980)
Barn swallows are native in all the biogeographic regions except Australia and Antarctica. The breeding range of barn swallows includes North America, northern Europe, northcentral Asia, northern Africa, the Middle East, southern China, and Japan. They winter in South America, South Asia, Indonesia, and Micronesia. (Terres, 1980)
Barn swallows are very adaptable birds. They can nest anywhere where there are open areas for foraging, a water source, and a sheltered ledge for their nest. They seek out open habitats of all types, including farms, and are commonly found in barns or other outbuildings. They also build nests under bridges, the eaves of old houses, and boat docks, as well as in rock caves and even on slow-moving trains.
Barn swallows are socially monogamous (one male mates and raises chicks with one female). However, barn swallows often copulate with other swallows that are not their mate. Therefore, they are probably actually polygamous. Barn swallows form breeding pairs each spring after they arrive on the breeding grounds. They form new pairs each spring, though the same two birds may nest together for several years.
Male barn swallows try to attract females by displaying their tails and singing. Female barn swallows seem to prefer males with long tails that are equal lengths on each side. Long tails and symmetry may be good signals of a male's health and fitness as a mate.
Adults that don't have a mate sometimes join breeding pairs, and help them to build a nest, defend the nest, incubate the eggs and brood the chicks. These "helpers" are usually male. They may mate with the female of the nest. (Bolzern, et al., 1997; Brown and Brown, 1999; De Lope and Moller, 1993; Moller, 1993; Moller, 1994a; Moller, 1994b)
Barn swallows usually breed between May and August. They usually raise two broods of chicks each summer. The male and female work together to build a nest. The nest is built of a mud shell, and is lined with grass and feathers. The female lays 3 to 7 eggs (average 5). Both parents incubate the eggs, which hatch in 13 to 15 days. The chicks are naked and helpless when they hatch. Both parents feed and protect the chicks, as well as removing their fecal sacs from the nest to keep it clean. The nestlings stay in the nest for about 20 days. When they are handled by humans they tend to leave the nest at least a day too early. The parents continue to care for the chicks for up to a week after they leave the nest. They feed them and lead them back to the nest at night to sleep. By two weeks after they have fledged from the nest, the chicks have left the area. They often travel quite far, visiting other barn swallow colonies. Young barn swallows are able to breed in spring after they hatch. Young barn swallows generally do not lay as many eggs as older birds. (Brown and Brown, 1999; McWilliams, 2000; Perrins, 1989; Terres, 1980)
In North America, both barn swallow parents incubate the eggs and feed the nestlings. However, females provide more parental care than males. During the nestling period, barn swallow parents may feed their chicks up to 400 times per day. Barn swallows feed their chicks a compressed pellet of insects that they carry in their throat. (Perrins, 1989; Terres, 1980)
Not much is known about the lifespan of these birds. The oldest wild barn swallow in North America lived 8 years, but this is considered to be unusual. Most barn swallows probably only live about 4 years. (Moller, 1994a; Moller, 1994b; Perrins, 1989; Terres, 1980)
Barn swallows are active during the day and are migratory. They nest in colonies, but defend a small territory around their nest. They are often seen in large groups sitting on telephone wires or other elevated structures. Barn swallows have individual songs and they often sing as a chorus. (Hebblethwaite and Shields, 1990; Moller, 1991)
A study in West Virginia found that barn swallows foraged within 1.2 km of their nests. In Europe, barn swallows foraged within 500 m of their nest. (Brown and Brown, 1999)
Barn swallows use vocalizations and body language (postures and movements) to communicate. Barn swallows sing, both individually and as a group. They have a wide variety of calls used in different situations, from predator alarm calls, to courtship calls, and calls of young in nests. Nestlings give off a faint chirp while begging for food. Barn swallows also make clicking noises, which they create by snapping their jaws together. (Brown and Brown, 1999)
Barn swallows are insectivores. Flies, grasshoppers, crickets, dragonflies, beetles, moths and other flying insects make up 99 % of their diet. They catch most of their prey while in flight, and are able to feed their young at the nest while flying.
Barn swallows forage opportunistically. They have been observed following tractors and plows, catching the insects that are disturbed by the machinery. They drink water by skimming the surface of a body of water while flying. (Brown and Brown, 1999; Perrins, 1989; Terres, 1980)
American kestrels and other hawks, such as sharp-shinned hawks and Cooper's hawks, eastern screech owls, gulls, common grackles, boat-tailed grackles, rats, squirrels, weasels, raccoons, bobcats, domestic cats, snakes, bullfrogs, fish and fire ants are predators of barn swallows. Barn swallows usually give alarm calls when predators come near. Most predators of barn swallows attack the nestlings, but hawks, falcons, and owls tend to hunt adults.
Barn swallows eat an enormous amount of insects and are very important in the control of their populations. Barn swallows are also a useful food source for many predators.
Cowbirds occasionally lay their eggs in barn swallow nests. If the barn swallows incubate the eggs and raise the cowbird chick, they are helping the cowbird population.
Barn swallows sometimes live in a symbiotic relationship with ospreys. The barn swallows nest inside or below an osprey nest, which is very big. By nesting near ospreys, the barn swallows are protected from predators, which are driven away by the ospreys. The ospreys benefit because the barn swallows give alarm calls when predators are nearby, alerting the ospreys. (Barker, et al., 1994; Brown and Brown, 1999; Wolfe, 1994)
Some humans feel that barn swallow nests are a nuisance, and are ugly when they are attached to buildings and other man-made structures. Large colonies in urban areas can also create heath risks for humans. Finally, the disease called salmonella can be transmitted through the feces of barn swallows. This poses a threat to animals that live near barn swallow colonies. (Brown and Brown, 1999; Perrins, 1989)
Barn swallows helps farmers get rid of insect pests that would affect them, their livestock, and their crops. They are a welcome insect predator on most farms. (Brown and Brown, 1999; Moore, 2001; Perrins, 1989)
In the past, barn swallows have benefited from human changes to natural landscapes. As humans destroyed vast areas of forest to convert to farmland, they created large areas of new habitat for swallows. Now, as farming is becoming more modernized, barn swallows may be becoming less abundant. Barns and hay lofts are now becoming enclosed, resulting in fewer places for barn swallows to build their nests. However, barn swallows continue to be widespread and common throughout their range. There are about 190,000,000 barn swallows in the world. (Moore, 2001)
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Kari Kirschbaum (editor), Animal Diversity Web.
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