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

Marie Read / Violet-green Swallow (Tachycineta thalassina), female in flight carrying a feather for nest lining, spring, Mono Lake, California, USA, July.

Marie Read / Violet-green Swallow (Tachycineta thalassina), female taking flight from tufa formation, carrying a feather for nest lining, spring, Mono Lake, California, USA, June.

Marie Read / Tree Swallow (Tachycineta bicolor), pair, one landing on perch while the other calls, New York, USA, April

Charlie Summers / Tree swallow (Tachycineta bicolor) two chicks that have left the nest, beg to be fed on the ground. Aurora, Colorado, USA, July

Charlie Summers / Tree Swallow (Tachycineta bicolor) adult seems to land on top of fledged chick as it feeds its offspring on the ground, Colorado, USA, July

Charlie Summers / Tree swallow (Tachycineta bicolor) female portrait, Aurora, Colorado, USA, July

Charlie Summers / Tree swallow (Tachycineta bicolor) adult landing next to begging chick, Aurora, Colorado, USA, July

Charlie Summers / Tree swallow (Tachycineta bicolor) adult feeding a fledgling chick on ground, Aurora, Colorado, USA, July

Loic Poidevin / Tree swallows (Tachyneta bicolor) mating, Pointe Pelee, Ontario, Canada May

Charlie Summers / Tree swallows (Tachycineta bicolor) two perform an aerial dance as they change the guard on their nest, Aurora, Colorado, USA June

Charlie Summers / Tree swallow (Tachycineta bicolor) female removing fecal sac from nest, Aurora, Colorado, USA, June

Charlie Summers / Tree swallow (Tachycineta bicolor) adult feeding aggressive chick that clamps its beak around the adults head, Aurora, Colorado, USA July

Charlie Summers / Tree Swallow (Tachycineta bicolor) approaching nest box calling to its mate. Aurora, Colorado, USA.

Charlie Summers / Tree Swallows (Tachycineta bicolor) in flight as one enters, and another leaves the nest box. Aurora, Colorado, USA.

Charlie Summers / Tree Swallow (Tachycineta bicolor) male leaving the nest box as the female approaches to take over nest duties. Aurora, Colorado, USA.

Charlie Summers / Tree Swallows (Tachycineta bicolor) in flight. Aurora, Colorado, USA.

Steve Gettle / Tree Swallow (Tachycineta bicolor) male calling, South Lyon, Michigan

Marie Read / Violet-green Swallow (Tachycineta thalassina) male using its bill to preen its feathers, while perched on tufa, Mono Lake, California, USA

Marie Read / Violet-green Swallow (Tachycineta thalassina) portrait of male facing camera, perched on tufa, Mono Lake, California, USA

Marie Read / Violet-green Swallow (Tachycineta thalassina) male perched on tufa formation, Mono Lake, California, USA

Marie Read / Violet-green Swallow (Tachycineta thalassina) female perched on tufa formation. This species nests in holes in the tufa formations. Mono Lake, California, USA.

Marie Read / Tree Swallow (Tachycineta bicolor) perched on Quaking Aspen (Populus tremuloides) branch, Mono Lake Basin, California, USA

Steve Gettle / Tree Swallow (Tachycineta bicolor) pair mating, Crane Creek State Park, Ohio

Steve Gettle / Tree Swallow (Tachycineta bicolor) males fighting to mate with female, Crane Creek State Park, Ohio

Steve Gettle / Tree Swallow (Tachycineta bicolor) pair courting, Maybury State Park, Michigan

Steve Gettle / Tree Swallow (Tachycineta bicolor) pair courting, Maybury State Park, Michigan

Steve Gettle / Tree Swallow (Tachycineta bicolor) pair courting, Maybury State Park, Michigan

Charlie Summers / Tree Swallow (Tachycineta bicolor) in flight, preparing to land at Western Bluebird nest box, Colorado, USA, North America

Gerrit Vyn / Pair of adult Tree Swallows (Tachycineta bicolor) perched on a nest box. Tompkins County, New York, USA, May.

Gerrit Vyn / Adult Tree Swallow (Tachycineta bicolor) perched on a branch, Tompkins County, New York, USA, May.

Donald M. Jones / Violet-green Swallow (Tachycineta thalassina) female carrying nesting material, western Montana

Donald M. Jones / Violet-green Swallow (Tachycineta thalassina) male, western Montana

Donald M. Jones / Violet-green Swallow (Tachycineta thalassina) male, western Montana

Donald M. Jones / Violet-green Swallow (Tachycineta thalassina) male, western Montana

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

Donald M. Jones / Tree Swallow (Tachycineta bicolor) male peeking out of nest cavity, western Montana

Donald M. Jones / Tree Swallow (Tachycineta bicolor) female at nest cavity, western Montana

Donald M. Jones / Tree Swallow (Tachycineta bicolor) male at nest cavity, western Montana

Donald M. Jones / Tree Swallow (Tachycineta bicolor) male at nest cavity with insect prey, western Montana

Scott Leslie / Tree Swallow (Tachycineta bicolor) parent feeding chick, Nova Scotia, Canada

Scott Leslie / Tree Swallow (Tachycineta bicolor) parent feeding chick, Nova Scotia, Canada

Scott Leslie / Tree Swallow (Tachycineta bicolor) poking head out of nesting box, Nova Scotia, Canada

Scott Leslie / Tree Swallow (Tachycineta bicolor) pair exchanging food on the fly, Tobeatic Wilderness Area, Nova Scotia, Canada

Scott Leslie / Tree Swallow (Tachycineta bicolor) landing near nest cavity with partner calling, Tobeatic Wilderness Area, Nova Scotia, Canada

Rolf Nussbaumer / Tree Swallow {Tachycineta bicolor} female at nest hole in Aspen tree, Rocky Mountain National Park, Colorado, USA, June

Nigel Bean / Violet green swallow (Tachycineata thalassina) California, USA

Shattil & Rozinski / Violet green swallow {Tachycineta thalassina} Colorado, USA

Shattil & Rozinski / Violet green swallow {Tachycineta thalassina} USA

Hanne & Jens Eriksen / Chilean swallow {Tachycineta meyeni} Patagonia, Chile, South America

Tom Vezo / Tree swallow {Tachycineta bicolor} Long Island, New York, USA

DAVID TIPLING / White winged swallow courtship {Tachycineta albiventer} Amazonia, Peru, South America

Doug Wechsler / Tree swallows copulating {Tachycineta bicolor} on top of bird box, Canada.

David Welling / Tree swallow {Tachycineta bicolor} male perching on branch, California, USA.

DAVID TIPLING / White winged swallow {Tachycineta albiventer} Amazonia, Peru

Tom Vezo / Tree Swallow (Tachycineta bicolor) singing from perch, Long Island, New York

Tom Vezo / Violet-green Swallow (Tachycineta thalassina), White Mountains, Arizona

Pete Oxford / White-winged Swallow (Tachycineta albiventer) and Proboscis Bat (Rhynchonycteris naso), Yasuni National Park, Amazon Rainforest, Ecuador

Steve Gettle / Tree Swallow (Tachycineta bicolor) male at nest cavity, Michigan

Sebastian Kennerknecht / Tree Swallow (Tachycineta bicolor), Clear Lake State Park, California

Mike Read / Violet-green swallow (Tachycineta thalassina) perched on wire, Yellowstone National Park, Wyoming, USA, June

Tom Vezo / Tree swallow flock migrating {Tachycineta bicolor} Cape May New Jersey USA

Tom Vezo / Tree swallow {Tachycineta bicolor} Long Is New York USA