The swallows and martins, or Hirundinidae, are a family of passerine birds found around the world on all continents except 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. There are around 83 species in 19 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 non-migratory.