The cliff swallow or American cliff swallow (Petrochelidon pyrrhonota) is a member of the passerine bird family Hirundinidae, the swallows and martins. The generic name Petrochelidon is derived from the Ancient Greek meaning "stone" and () "swallow", and the specific name pyrrhonota comes from purrhos meaning "flame-coloured" and -notos "-backed".
Cliff swallows are extremely social songbirds that can be found in large nesting colonies reaching over 2,000 nests. They are frequently seen flying overhead in large flocks during migration, gracefully foraging over fields for flying insects or perching tightly together on a wire preening under the sun. They build their nests tightly together, on top of one another, under bridges or alongside mountain cliffs.
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left|thumb|Juvenile cliff swallow
thumb|right|Juvenile cliff swallow in a gourd-shaped mud nest
The male and female have identical plumage, therefore sexing them must be done through palpation of the cloaca. The juvenile cliff swallows' white forehead and throat markings have high variance between unrelated individuals compared with those from the same clutch. All the bird species in this order have four toes, three pointing forward and one pointing backwards (anisodactylous), that enable them to perch with ease. Additionally, all species in the family Hirundinidae have short-flat bills for their largely insectivorous diets, small feet because they spend much of their time in flight, and long wings for energy-efficient flight. In addition, three core genera of hirundo were established on the basis of molecular studies: Hirundo sensu stricto, containing the barn swallow; Cecropis, containing the red-rumped swallow; and Petrochelidon, containing the cliff swallow. The majority of nesting colonies are situated in close proximity to fields, ponds, and other ecosystems that would hold a large variety of flying insect populations to sustain their energy requirements during the breeding season. They nest at the church of Mission San Juan Capistrano, where their annual migration is culturally celebrated. A 1940 song by Leon René, "When the Swallows Come Back to Capistrano", celebrates this event.
Behaviour
Cliff swallows live in a colonial lifestyle during the breeding season, composed of a large number of pairs per nesting site. The cliff swallows have an unusually large parasite community that includes ectoparasites, ticks, fleas and swallow bugs, among others. These parasite infestations have been shown to negatively affect juvenile growth and developmental rates. The cliff swallows have an "aggressive and fearless" personality in comparison to their relatives the barn swallows, who were noted as being "timid and fearful".
right|thumb|Cliff swallow egg
Once the house sparrows pick their nest, they will bring in grass and other materials making it impossible for the cliff swallows to re-establish their place. Thus, the colonies with house sparrow predation have an overall lower success rate and fewer previous-year nests being used.