Pete Cairns / Least chipmunk on pine stump {Eutamias minimus} Yellowstone NP, USA

Ingo Arndt / Bison male sniffing female during rut {Bison bison} Yellowstone NP, WY, USA

John Waters / Sand martin (Riparia riparia) taking swan feather from surface of River Wy to line its nest located nearby, Herefordshire, UK, May.

David Kjaer / Lower Falls (308 ft) Yellowstone river, Yellowstone National Park, WY, USA

David Kjaer / Male Moose swimming across Snake river {Alces alces} Grand Teton NP, WY, USA

David Kjaer / Blue / dusky grouse calling {Dendragopus obscurus} Yellowstone, WY, USA

Jeff Vanuga / Lodgepole pine forest after heavy fall of snow, Yellowstone NP, WY, USA. 1998

Jeff Vanuga / Wild fire rages through Lodgepole pine forest, Yellowstone NP, WY, USA. 1998

Jeff Vanuga / Wild fire rages through Lodgepole pine forest, Yellowstone NP, WY, USA. 1998

Pete Cairns / Bighorn sheep fitted with radio tracking collar {Ovis canadensis} Yellowstone NP, WY,USA

Bernard Castelein / Red deer / Elk male in rutting season,Yellowstone NP, Wyoming, USA

Hermann Brehm / American avocet display {Recurvirostra americana} Yellowstone NP, WY, US

Pete Cairns / Least chipmunks investigate camera {Eutamias minimus} Yellowstone NP, WY, USA

Pete Cairns / Least chipmunk {Eutamias minimus} on head of photographer Mark Hamblin in Yellowstone NP, WY, USA Model released.

Hermann Brehm / Young Pronghorn antelopes {Antilocapra americana} Yellowstone NP, Wyoming

Niall Benvie / Pronghorn antelope female, Yellowstone NP, Wyoming, USA

Bernard Castelein / Least chipmunk feeds on seeds, Yellowstone NP, USA.

Mike Read / Uinta ground squirel on burrow {Spermophilus armatus} Grand Teton NP, WY, USA