Alan Murphy / Mountain Bluebird (Sialia currucoides) male, British Columbia, Canada

Donald M. Jones / Mountain Bluebird (Sialia currucoides) male, Montana

Donald M. Jones / Mountain Bluebird (Sialia currucoides) male in nest cavity, Troy, Montana

Oscar Dewhurst / Mountain bluebird (Sialia currucoides). Yellowstone National Park, Wyoming, USA. September.

Gerrit Vyn / Mountain bluebird (Sialia currucoides) at nest cavity with prey. Sublette County, Wyoming, USA. June.

Gerrit Vyn / Mountain bluebird (Sialia currucoides) female returning to nest cavity with food. Sublette County Wyoming, USA. June.

Gerrit Vyn / Mountain bluebird (Sialia currucoides) male, returning to its nest with food. Sublette County, Wyoming, USA. June.

Marie Read / Mountain bluebirds (Sialia currucoides), three fledglings, Parker Canyon, Mono Lake Basin, California, USA, June.

Visuals Unlimited / Mountain Bluebird (Sialia currucoides) sitting on a wire fence with an insect larva in its bill in the grasslands of Canada.

Visuals Unlimited / Mountain Bluebird (Sialia currucoides), Canada.

Visuals Unlimited / Mountain Bluebird (Sialia currucoides), Canada.

Marie Read / Mountain Bluebird (Sialia currucoides), male hovering to investigate potential nest hole in burned Jeffrey Pine (Pinus jeffreyi), Mono Lake Basin, California, USA, June.

Marie Read / Mountain Bluebird (Sialia currucoides), male hovering to investigate potential nest hole in burned Jeffrey Pine (Pinus jeffreyi), Mono Lake Basin, California, USA, June.

Diane McAllister / Male Mountain bluebird (Sialia currucoides) resting on a perch in Mammoth Springs. Yellowstone National Park, Wyoming, USA, May

Gerrit Vyn / Mountain Bluebird (Sialia currucoides) male perched in branch, Douglas County, Washington, USA, April.

Marie Read / Mountain Bluebird (Sialis currucoides), outside its nest hole in Aspen trunk, carrying caterpillar prey in its bill for young, Mono Lake Basin, California, USA

Marie Read / Mountain Bluebird (Sialis currucoides) carrying inspect prey in its bill for young, Mono Lake Basin, California, USA

Marie Read / Mountain Bluebird (Sialia currucoides) male with food (caterpillar) for young in its bill, Mono Basin, California, USA (Digitally retouched image - stick removed at top)

Marie Read / Mountain Bluebird (Sialis currucoides) male looking out of its nest hole in Aspen trunk, Mono Lake Basin, California, USA

Marie Read / Mountain Bluebird (Sialia currucoides) female at nest hole in burned Jeffrey Pine (Pinus jeffreyi) Mono Basin, California, USA

George Sanker / Mountain bluebird (Sialia currucoides) pair, Grand Teton National Park, Wyoming, USA, May

David Tipling / Mountain Bluebird {Sialia currucoide} feeding on Juniper berries, New Mexico, USA, January

Rolf Nussbaumer / Mountain Bluebird {Sialia currucoides} adult male with prey, Rocky Mountain National Park, Colorado, USA, June

Thomas Lazar / Mountain bluebird {Sialia currncoides} female, USA

Thomas Lazar / Mountain bluebird {Sialia currucoides} female, USA

Tom Vezo / Mountain Bluebird {Sialia currucoides} female perching on barbed wire with prey, Montana, USA.

Rolf Nussbaumer / Mountain bluebird {Sialia currucoides} male on post, Grand Teton NP, Wyoming, USA

Tom Vezo / Mountain bluebird, male at nest hole {Siala currucoides} Arizona, USA.

Tom Vezo / Mountain bluebird, male, with insect prey {Siala currucoides} Arizona, USA.

Tom Vezo / Mountain bluebird male {Sialia currucoides} Montana, USA

Alan Murphy/ BIA / Mountain Bluebird (Sialia currucoides) male with insect prey, British Columbia, Canada

Alan Murphy/ BIA / Mountain Bluebird (Sialia currucoides) male with insect prey, British Columbia, Canada

Alan Murphy/ BIA / Mountain Bluebird (Sialia currucoides) male with insect prey, British Columbia, Canada

Donald M. Jones / Mountain Bluebird (Sialia currucoides) male, southwestern Montana

Donald M. Jones / Mountain Bluebird (Sialia currucoides) male, southwestern Montana

Steve Gettle / Mountain Bluebird (Sialia currucoides) male, Yellowstone National Park, Wyoming

Alan Murphy/ BIA / Mountain Bluebird (Sialia currucoides) male with insect prey, British Columbia, Canada

Alan Murphy/ BIA / Mountain Bluebird (Sialia currucoides) female with insect prey, British Columbia, Canada

Alan Murphy/ BIA / Mountain Bluebird (Sialia currucoides) male with insect prey, British Columbia, Canada

Alan Murphy/ BIA / Mountain Bluebird (Sialia currucoides) female with butterfly prey, British Columbia, Canada

Alan Murphy/ BIA / Mountain Bluebird (Sialia currucoides) male flying with insect prey, British Columbia, Canada

Alan Murphy/ BIA / Mountain Bluebird (Sialia currucoides) male flying with insect prey, British Columbia, Canada

Alan Murphy / Mountain Bluebird (Sialia currucoides) male, British Columbia, Canada

Alan Murphy / Mountain Bluebird (Sialia currucoides) male, British Columbia, Canada

Alan Murphy / Mountain Bluebird (Sialia currucoides) male with prey at nest cavity, British Columbia, Canada

Donald M. Jones / Mountain Bluebird (Sialia currucoides) male, Montana

Alan Murphy / Mountain Bluebird (Sialia currucoides) male, Montana

Robert Royse / Mountain Bluebird (Sialia currucoides), New Mexico