Swallow world

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 as the common name for Hirundo rustica in the United Kingdom and Ireland. 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. 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.