Hirundinidae

The swallows, martins, and saw-wings, or Hirundinidae, are a family of passerine birds 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 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, no scientific distinction between these two groups is made.[3] In the New World, "martin" is reserved for members of the genus Progne. (These two systems are responsible for the sand martin being called "bank swallow" in the New World.)