Swallow
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. Highly adapted to aerial feeding, they have a distinctive appearance. The term "swallow" is used colloquially in Europe as a synonym for the barn swallow. Around 90 species of Hirundinidae are known,[1] divided into 19 genera, with the greatest diversity found in Africa, which is also thought to be where they evolved as hole-nesters.[2] They also occur on a number of oceanic islands. A number of European and North American species are long-distance migrants; by contrast, the West and South African swallows are nonmigratory.
This article is about the family of birds. For the action, see Swallowing. For other uses, see Swallow (disambiguation).This family comprises two subfamilies: Pseudochelidoninae (the river martins of the genus Pseudochelidon) and Hirundininae (all other swallows, martins, and saw-wings). In the Old World, the name "martin" tends to be used for the squarer-tailed species, and the name "swallow" for the more fork-tailed species; however, this distinction does not represent a real evolutionary separation.[3] In the New World, "martin" is reserved for members of the genus Progne. (These two systems are responsible for the same species being called sand martin in the Old World and bank swallow in the New World.)
Taxonomy and systematics[edit]
The family Hirundinidae was introduced (as Hirundia) by the French polymath Constantine Samuel Rafinesque in 1815.[4][5] 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).[6] Phylogenetic analysis has shown that the family Hirundinidae is sister to the cupwings in the family Pnoepygidae. The two families diverged in the early Miocene around 22 million years ago.[7]
Within the family, a clear division exists between the two subfamilies, the Pseudochelidoninae, which are composed of the two species of river martins,[8][9] and the Hirundininae, into which the remaining species are placed. The division of the Hirundininae has been the source of much discussion, with various taxonomists variously splitting them into as many as 24 genera and lumping them into just 12. Some agreement exists that three core groups occur within the Hirundininae, the saw-wings of the genus Psalidoprocne, the core martins, and the swallows of the genus Hirundo and their allies.[10] The saw-wings are the most basal of the three, with the other two clades being sister to each other. The phylogeny of the swallows is closely related to evolution of nest construction; the more basal saw-wings use burrows as nest, the core martins have both burrowing (in the Old World members) and cavity adoption (in New World members) as strategies, and the genus Hirundo and its allies use mud nests.[11]
