The Barn Swallow is an agile and aerodynamic migratory bird that breeds in Europe and winters in sub-Saharan Africa. They have metallic blue upperparts, red forehead and throat, and white underparts. The tail feathers are elongated and forked. Distinguished from its relative the house martin by its svelte physique, red throat and long forked tail feathers.
Swallows are insectivorous, feeding on insects that they hunt in flight. They have an impressive acrobatic flight, occupying the lower airspace below the house martin and are often seen flying very low to the ground. They do not fly particularly fast, reaching speeds of up to 40 km per hour, but they have an acrobatic agility in the air.
Swallows have lived in long association with humans, building cup-shaped mud nests in protected places on human structures, and their feeding habits of eating large numbers of insects means that they are generally tolerated by humans. Swallows have historical and mythological associations; tattoos of swallows for sailors symbolising nautical miles travelled, and the legend that swallows removed the thorns from the crown of Christ, and so (as a form of mythological preservation) it was considered unlucky to disturb them.
The arrival of the swallows, although now increasingly earlier as a result of climate change is considered the announcement of spring. They have a cheerful and chattery call. In 2014 the swallow was SEO's bird of the year due to its dramatic decline in the last decade.
Swallows consume large quantities of insects. They feed on a variety of insects; flies, aphids, mosquitoes and flying ants. They gather in communal roosts after breeding, sometimes thousands of them in reed beds. Reed beds are an important source of food before and during migration; the swallow is a diurnal migrant that can feed while traveling low on land or water.
The male swallow returns to the breeding areas before the females to select the nest site, which is then announced to the females with a circular flight and call. The success of the male's breeding is related to the length of the tail feathers, a longer tail being more attractive to the female. Tail feathers are an indicator of the health and genetic strength of males, males with longer tail feathers tend to have a longer life and are more resistant to disease. Northern European males have longer tail feathers than Southern European males.
The breeding season for the swallow is variable; in Spain it is usually from February or March to early or mid September, although some late breeding ends in October. In Northern Europe it usually begins in late May or early June and ends at the same time as the breeding season for the more southern birds. Both sexes defend the nest, but the male is particularly aggressive and territorial. Once established, the pairs remain together to reproduce for life, but copulation between pairs is common, making this species genetically polygamous despite being socially monogamous.
The female lays 4 or 5 eggs, chicks are born after 13-14 days and take quite a while to develop, and about 21 days to fly. They lay two or three clutches during the breeding season which is a way of maintaining the population due to the large losses during migration.
Swallows typically nest in sheltered places, in inner courtyards, inside accessible buildings such as barns and stables. The nest is built by both sexes with small clay balls collected in their beaks and lined with grass, feathers, algae or other soft materials. They return to the same nesting sites year after year. The nest is repaired and reused by cleaning the old feathers and adding new mud to the edge of the nest. Females will lay more eggs and at an earlier date with males who are better at nest building, the opposite being true with males who are not.
It takes a couple of swallows up to approximately 1000 trips to build a nest with the mud they collect. The destruction of nests and the availability of nesting sites is one of the reasons for the recent decline in the population. The expense of energy to rebuild a nest that might otherwise be repaired after its long migratory journeys is enormous for a small bird and contributes to its decline.
Swallows are long-distance migrants that winter in sub-Saharan Africa and breed in Europe. Some birds follow the west coast of Africa avoiding the Sahara, others travel further east and down the Nile Valley.
Swallows don´t gain a great deal of weight before migration, as they migrate during the day at low altitudes and find food on the way. Despite accumulating some fat reserves before crossing large areas such as the Sahara desert, they are vulnerable to starvation during these journeys. The migration is a dangerous time and many birds die of hunger, exhaustion and in storms. Migrating swallows cover 200 miles a day, mostly during the day, at speeds of 17-22 miles per hour. The return trip to Africa takes about six weeks.
One of the biggest problems swallows face is the indiscriminate use of pesticides, which kill the insects that are their main source of food. The deliberate removal of nesting sites with the excuse that they dirty buildings and the lack of new nesting sites is also a problem. Another problem for swallows (and also for house martins) is the shortage of material to build their nests in urban areas due to the shortage of swamps and wetlands. The swallow was SEO bird of the year in 2014 because of the huge population decrease it has suffered and it appears in the catalog of threatened species in Spain.