21, see text The swallows, martins, and saw-wings, or Hirundinidae are a family of passerine songbirds found around the world on all continents, including occasionally in Antarctica.

[2] Around 90 species of Hirundinidae are known, divided into 21 genera, with the greatest diversity found in Africa, which is also thought to be where they evolved as hole-nesters.

A number of European and North American species are long-distance migrants; by contrast, the West and South African swallows are nonmigratory.

[5][6] The Hirundinidae are morphologically unique within the passerines, with molecular evidence placing them as a distinctive lineage within the Sylvioidea (Old World warblers and relatives).

[12] The genus level cladogram shown below is based on a molecular phylogenetic study by Drew Schield and collaborators that was published in 2024.

[13] The choice of genera and the number of species is taken from the list of birds maintained by Frank Gill, Pamela C. Rasmussen and David Donsker on behalf of the International Ornithological Committee (IOC).

[16] Swallows have two foveae in each eye, giving them sharp lateral and frontal vision to help track prey.

[17] Like the unrelated swifts and nightjars, which hunt in a similar way, they have short bills, but strong jaws and a wide gape.

[21] Their legs are short, and their feet are adapted for perching rather than walking, as the front toes are partially joined at the base.

[11] The most common hirundine plumage is glossy dark blue or green above and plain or streaked underparts, often white or rufous.

The sexes show limited or no sexual dimorphism, with longer outer tail feathers in the adult male probably being the most common distinction.

Land-use changes have also caused some species to expand their range, most impressively the welcome swallow, which began to colonise New Zealand in the 1920s, started breeding in the 1950s, and is now a common landbird there.

In general, the male selects a nest site, and then attracts a female using song and flight and (dependent on the species) guards his territory.

[11] These roosts can be enormous; one winter-roosting site of barn swallows in Nigeria attracted 1.5 million individuals.

[33] Nonsocial species do not form flocks, but recently fledged chicks may remain with their parents for a while after the breeding season.

Species in Africa have been recorded eating the seeds of Acacia trees, and these are even fed to the young of the greater striped swallow.

[11] Swallows in the genera Hirundo, Ptyonoprogne, Cecropis, Petrochelidon, Atronanus and Delichon build mud nests close to overhead shelter in locations that are protected from both the weather and predators.

In historical times, the introduction of man-made stone structures such as barns and bridges, together with forest clearance, has led to an abundance of colony sites around the globe, significantly increasing the breeding ranges of some species.

Migratory species often return to the same breeding area each year, and may select the same nest site if they were previously successful in that location.

[11] Swallows are able to produce many different calls or songs, which are used to express excitement, to communicate with others of the same species, during courtship, or as an alarm when a predator is in the area.

This is presumed to be the reason behind the decline of the critically endangered white-eyed river martin, a species that is only known from a few specimens collected in Thailand.

[52] Because of the long human experience with these conspicuous species, many myths and legends have arisen as a consequence, particularly relating to the barn swallow.

[11] Roman historian Pliny the Elder described a use of painted swallows to deliver a report of the winning horses at a race.

[53] There is also the Korean folktale of Heungbu and Nolbu, which teaches a moral lesson about greed and altruism through the mending of a swallow's broken leg.

[54] During the 19th century, Jean Desbouvrie attempted to tame swallows and train them for use as messenger birds, as an alternative to war pigeons.

He succeeded in curbing the migratory instinct in young birds and persuaded the government of France to conduct initial testing, but further experimentation stalled.

[53][55] Subsequent attempts to train homing behaviour into swallows and other passerines had difficulty establishing a statistically significant success rate, although the birds have been known to trap themselves in a cage repeatedly to get to the bait.

This probably arose from the fact that swallows are land-based birds, so their appearance informs a sailor that he or she is close to shore.