Alan Murphy / Tree Swallow (Tachycineta bicolor) male, British Columbia, Canada

Tom Vezo / Purple Martin (Progne subis) and Tree Swallow (Tachycineta bicolor) mixed group perching on branch, Crane Creek, Ohio

Donald M. Jones / Tree Swallow (Tachycineta bicolor) in nest cavity, Montana

John Chan / Tree swallow (Tachycineta bicolor) feeding chicks, Bolsa Chica Ecological Reserve, California, USA, June.

Dave Bevan / Flock of Sand martins (Riparia riparia) preening, perched on tree roots adjacent to nesting bank, Carmarthenshire, Wales, UK, April.

Phil Savoie / Tree swallow (Tachycineta bicolor) in flight catching insects over the Madison River, Montana, USA. June.

Phil Savoie / Tree swallow (Tachycineta bicolor) in flight catching insects over the Madison River, Montana, USA. June.

Phil Savoie / Tree swallow (Tachycineta bicolor) flying hunting insects over the Madison River, Montana, USA, June.

Phil Savoie / Tree swallow (Tachycineta bicolor) in flight feeding over the Madison River, Montana, USA, May.

Phil Savoie / Tree swallows (Tachycineta bicolor), perched on wire, calling aggressively to each other, Madison River, Montana, USA, June.

Phil Savoie / Tree swallow (Tachycineta bicolor) perched on wire, Madison River, Montana, USA. June.

Phil Savoie / Tree swallow (Tachycineta bicolor), in flight catching insects over the Madison River, Montana, USA, June.