Hirundo rustica
barn swallow

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 and can nest anywhere with open areas for foraging, a water source, and a sheltered ledge. They seek out open habitats of all types, including agricultural areas, and are commonly found in barns or other outbuildings. They will 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.

While migrating, they tend to fly over open areas, often near water or along mountain ridges. Barn swallows generally nest below 3000 m elevation. (McWilliams, 2000; Terres, 1980)

Barn swallows are small birds. They range in size from 14.6 to 19.9 cm long, with 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 are similar in appearance, though females tend to be less vibrantly colored and have shorter outer tail-streamers.

Asymmetry of physical characteristics in barn swallows tends to be transmitted to the young in distinct parent to offspring patterns. Tail asymmetry tends to pass from father to son and from mother to daughter. Alternatively, wing asymmetry does not appear to transfer at all on a reliable basis from parent to offspring.

Six subspecies of Hirundo rustica are recognized. (Moller, 1994a; Moller, 1994b; Terres, 1980)

Barn swallows are socially monogamous. However, extra-pair copulations are common, making this species genetically polygamous. Breeding pairs form each spring after arrival on the breeding grounds. Pairs re-form each spring, though pairs that have nested together successfully may mate together for several years. Males try to attract females by spreading their tails to display them and singing.

Several studies have researched sexual selection in barn swallows. Moller (1994) documented female barn swallows selecting for symmetrical wings and tails in potential mates. Males exhibiting greater symmetry acquired mates more quickly than did asymmetric males. Asymmetry can result from genetic factors such as inbreeding or mutations as well as from environmental stress such as food deficiency, parasite infestation, or the presence of pathogens. Moller observed that individuals affected by these factors not only exhibited asymmetry, but also decreased strength and longevity. Therefor, females that selected symmetrical mates would presumably be selecting superior mates. In addition to selecting for symmetry, females also tend to select males with longer tail feathers. Moller observed a connection between the tail length of male barn swallows and their offspring’s vitality and longevity. Males with longer tail feathers exhibit traits of greater longevity which is passed on to their offspring. Females thus gain an indirect fitness benefit from this form of selection, as longer tail feathers indicate a genetically stronger individual who will produce offspring with enhanced vitality. Individuals with longer tails have also been observed to demonstrate greater disease resistance than their short-tailed counterparts. There is also evidence that males select female mates with long tails.

Unmated adults often associate with a breeding pair for up to an entire season. Though these "helpers" do not usually feed the young, they may help with nest defense, nest building, incubation and brooding. "Helpers" are predominantly male, and may succeed in mating with the resident female, leading to polygyny. (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, but this varies greatly with location. They usually raise two broods of chicks each summer. Both birds of a pair make the nest. They build the shell of mud, and line it 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 fecal sacs from the nest. The nestlings remain in the nest for about 20 days before fledging. When barn swallows are handled by humans they tend to attempt to fledge at least a day too early. The parents continue to care for the chicks for up to a week after fledging, feeding them and leading them back to the nest to sleep. By two weeks after fledging, the barn swallow chicks have dispersed and often travel widely to other barn swallow colonies. Young barn swallows are able to breed in the first breeding season after they have hatched. Generally, young barn swallows do not produce as many eggs as do 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 do males. During the nestling period, barn swallow parents may feed their nestlings up to 400 times per day. Barn swallows feed their chicks insects compressed into a pellet, which is transported to the nest in the parent’s throat. Although all swallows are socially monogamous, barn swallows differ from most swallow species in the sharing of parental care. Juveniles from the first brood of the season have even been observed assisting their parents in feeding a second brood. (Perrins, 1989; Terres, 1980)

The average lifespan of barn swallows is 4 years. Barn swallows of 8 years of age have been documented, but these are considered the exception. Survival prospects and longevity appear to increase with tail length and wing and tail symmetry. (Moller, 1994a; Moller, 1994b; Perrins, 1989; Terres, 1980)

Barn swallows are diurnal and migratory. They have individual songs and often sing as a chorus.

Barn swallows are often seen in large social groups sitting on telephone wires or other elevated structures. They also nest colonially, probably as a result of the distribution of high quality nest sites. Within a colony, barn swallows defend a territory around their nest. In European barn swallows, these territories range in size from about 4 to 8 square meters. (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 mainly escape predators by being swift and agile in flight and by building their nests in places that are difficult for predators to reach. (Barker, et al., 1994; Brown and Brown, 1999)

Although incidents of cowbirds parasitizing barn swallow nests are rare, they have been documented. A 1994 observation of 67 Barn Swallow nests found two of these nests to contain cowbird eggs, which were laid by the parent cowbird and left in the barn swallow nest in a parasitic fashion for the barn swallows to raise. Each of these nests contained 1 cowbird egg and both eggs were incubated by the barn swallows along with their own eggs. However, only one of the cowbird eggs hatched. The single cowbird hatchling fledged normally, thus demonstrating that barn swallows are capable of acting as cowbird hosts.

Barn swallows frequently engage in a symbiotic relationship with ospreys, coexisting in a single nesting area to the mutual benefit of both species. Barn swallows will nest either below a much larger osprey nest or in a portion of an abandoned osprey nest. By nesting near an osprey population, the barn swallows receive protection from birds of prey, which are driven away from the nests by the much larger ospreys. In return, ospreys are alerted to the presence of these predators by the barn swallows which give alarm calls when predators are nearby.

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. (Barker, et al., 1994; Brown and Brown, 1999; Wolfe, 1994)

Barn swallows are quite effective in reducing insect pest populations. They also can serve as an indicator or trigger organism, indicating possible environmental trouble, as declines in their relatively abundant numbers may precede other more obvious effects of environmental stress. (Moore, 2001; Perrins, 1989)

Some humans feel that barn swallow nests are a nuisance, and are unsightly when they are attached to buildings and other man-made structures. Large colonies in urban areas can also create detrimental cleanliness and health issues for humans. Finally, salmonella can be transmitted through their feces, posing a threat to livestock that live in close proximity to barn swallow colonies. (Brown and Brown, 1999; Perrins, 1989)

Barn swallow populations are generally considered to be stable and sufficiently extensive. However, declines in the amount of acreage devoted to agriculture in recent years have resulted in reduced barn swallow numbers. This can be attributed to a reduction in habitat as the barns and outbuildings which once housed barn swallows, give way to more urban settings. Another contributing factor is the reduction in food supply. Insects attracted by the presence of livestock and the ideal surrounding habitat are the primary food source for barn swallows living in agricultural areas. Locations where farming has ceased exhibit a 50% reduction in insect populations.

Barn swallows continue to be widespread and common throughout their range. There are an estimated 190,000,000 individuals worldwide. (Brown and Brown, 1999; Moore, 2001)