Common and widespread breeder in open areas, nesting in holes in dead trees (often near water) and nest-boxes. A tough swallow, many winter in S, with a few hardy ones much further n. On migration, they often line telegraph wires or form tight flocks that look like a swarm of gnats in the distance. The common swallow in late fall. ID: A neat looking medium-sized swallow with balanced proportions. Tail square-ended or slightly forked. Two-tone with clean divide between dark upperparts and pale underparts. Adult: iridescent blue upperparts, darker on wings, tail, and through eye. Brown replaces blue in some ♀. Molts on fall migration, creating a patchwork of brown and blue feathers. Tertials with bold white tips. Juv: upperparts uniformly brown, darker through eye and with narrow white tips to tertials. Many show a buffier collar and breast sides, and these molt adult-type feathers through fall and appear as adults.