Major habitats for swallows and martins include forested ecosystems close to lakes, rivers, streams, and wetlands, as well as wooded savanna and prairies. Their habitats are normally open areas with an abundant supply of flying insects as prey. The proximity of appropriate nest-site habitat is also critical. Some swallow species utilize tree cavities for nesting, while others require mud or sand banks in which nesting tunnels can be dug, and yet others demand access to soft mud as a material used to construct clinging nests on cliffs or other vertical structures. Swallows and martins have fewer habitat restrictions during the non-breeding season, and they may migrate or wander extensively at that time.
Specific habitat requirements differ greatly among genera in the swallow family. Species in the genus Hirundo, for example, have specialized habitat needs ranging from desert to tropical rainforest, and from highlands to seacoasts. Some swallow species have greatly expanded their range of habitat utilization by taking advantage of human-built structures for nesting. For instance, barn swallows (Hirundo rustica) commonly nest on or inside of farm buildings and cottages, whereas they were previously restricted to using caves and cliffs in coastal areas. This adaptive change to utilizing anthropogenic habitats has allowed barn swallows to expand their range and overall abundance. Similarly, cliff swallows (H. pyrrhonota) often build their nests in protected locations on bridges and buildings. Most species of hirundines, however, continue to use only natural nesting sites.
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