-Click pic to enlarge (taken by Malcolm Wilton-Jones in Llíria, Spain~
The Barn Swallow (Hirundo rustica) is the most widespread species of swallow in the world. It is a distinctive passerine bird with blue upperparts, a long, deeply forked tail and curved, pointed wings. It is found in Europe, Asia, Africa and the Americas.
The preferred habitat of the Barn Swallow is open country with low vegetation, such as pasture, meadows and farmland, preferably with nearby water. It normally uses man-made structures to breed and consequently has spread with human expansion. Both sexes help build a cup nest from mud pellets in barns or similar structures and feeds on insects caught in flight. This species lives in close association with humans, and its insect-eating habits mean that it is tolerated by man.
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.
The adult male Barn Swallow is 6.7–7.5 in long including 0.8–2.8 in of elongated outer tail feathers. It has a wingspan of 12.6–13.6 in and weighs 0.56–0.78 oz.
The 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. 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.
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 copulation is common. Males guard females actively to avoid being cuckolded.
Swallows gather in communal roosts after breeding, sometimes thousands strong.
The song of the 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 alarm calls include a sharp siflitt for predators like cats and a flitt-flitt for birds of prey.
H/t Project Noah