Carol Walker / Mustang herd standing in snow. Black Hills Wild Horse Sanctuary, South Dakota, USA. January 2017.

John Shaw / Late afternoon light warms the colors in the Yellow Mounds area, Badlands National Park, South Dakota, USA, September.

Ingo Arndt / Prairie rattlesnake (Crotalus viridis viridis), threat display, South Dakota, USA September. Sequence 1 of 3

Klein & Hubert / American bison (Bison bison) bull, North Dakota, USA.

Jack Dykinga / Cheyenne River Sioux Tribal Park with severe storm clouds at sunset amid vast grassland, South Dakota, USA

John Cancalosi / Pronghorn Antelope (Antilocapra americana) head portrait, South Dakota, USA

John Cancalosi / Feral Burro / Donkey foal (Equus asinus) head portrait lying in long grass, Custer State Park, South Dakota, USA

John Cancalosi / Feral Burro / Donkey (Equus asinus) female and foal, portrait standing in long grass, Custer State Park, South Dakota, USA

Charlie Summers / Three Western Black-tailed Prairie Dogs (Cynomys ludovicianus) at entrance to burrow. Cheyenne River drainage south of Hot Springs, South Dakota, USA

Charlie Summers / Cowboy working with herd of American Bison (Bison Bison) during the 2010 buffalo roundup in Custer State Park; South Dakota, September 2010

Charlie Summers / Mustang (Equus caballus) herd trotting in light snow covered prairie, IRAM Wild Horse Sanctuary south of Hot Springs, South Dakota, USA, May

Charlie Summers / American bison (Bison bison) herd roaming the plains, Custer State Park, South Dakota, USA, September

Ingo Arndt / American Bison (Bison bison) herd stampeding, South Dakota, USA

Ingo Arndt / American Bison (Bison bison) herd stampeding, South Dakota, USA

Ingo Arndt / American Bison (Bison bison) herd grazing on a hillside, South Dakota, USA

Ingo Arndt / Mount Rushmore National Memorial, South Dakota, USA, September 2009

Ingo Arndt / American Bison (Bison bison) head portrait of male scenting air, South Dakota, USA

Ingo Arndt / View of Badlands National Park, with shadows cast between mountain peaks, and sediment layers visible, South Dakota, USA. September 2009.

Ingo Arndt / View of Badlands National Park, with shadows cast between mountain peaks, and sediment layers visible, South Dakota, USA. September 2009.

Gerrit Vyn / Adult Whooping Cranes (Grus americana) from the wild population, foraging in a corn field during spring migration. Central South Dakota, USA, April.

Gerrit Vyn / Aggressive encounter between two male Greater Prairie-Chickens (Tympanachus cupido) on a lek. During these aggressive encounters, males lower their pinnae feathers, deflate their air sacs, leap into t...

Gerrit Vyn / Aggressive encounter between two male Greater Prairie-Chickens (Tympanachus cupido) on a lek. During these aggressive encounters, males lower their pinnae feathers, deflate their air sacs, leap into t...

Jack Dykinga / Hoodoo with rock cap on textured Dakota stone and softer Entrada sandstone, sunset, Glen Canyon National Recreation Area, Arizona, USA

Kirkendall-Spring / View overlooking the badlands from Scenic Loop Drive, Theodore Roosevelt NP, North Dakota, USA

Kirkendall-Spring / Clay formation in the prairies near Round Up Camp, Theodore Roosevelt NP, North Dakota, USA

GRANT MCDOWELL / Flooded town, Grand Forks, North Dakota, USA. April 1997

Grant McDowell / Aerial view of flooded town, Grand Forks, North Dakota USA April 1997

GRANT MCDOWELL / Aerial view of flooded land at Grand Forks North Dakota USA April 1997

Thomas Lazar / Black tailed prairie dog (Cynomys ludovicianus) alert female, Custer State Park, South Dakota, USA

Jim Brandenburg / Giant Walking Stick (Megaphasma dentricus) camouflaged among prairie grasses, North Dakota

Jim Brandenburg / Ponderosa Pine (Pinus ponderosa) tree on prairie, Wind Cave National Park, South Dakota

Jeff Foott / Pronghorn Antelope (Antilocapra americana) male in grassland, Wind Cave National Park, South Dakota

Jeff Foott / Little Missouri River, Theodore Roosevelt National Park, North Dakota

Jeff Foott / Sandstone rock formations, Theodore Roosevelt National Park, North Dakota

Donald M. Jones / Black-tailed Prairie Dog (Cynomys ludovicianus) group, South Dakota

Donald M. Jones / Black-tailed Prairie Dog (Cynomys ludovicianus) pair greeting, South Dakota

Donald M. Jones / Black-tailed Prairie Dog (Cynomys ludovicianus) pair greeting, South Dakota

Yva Momatiuk & John Eastcott / Black-tailed Prairie Dog (Cynomys ludovicianus) on alert, Theodore Roosevelt National Park, North Dakota

Steve Gettle / Western Grebe (Aechmophorus occidentalis) pair in courtship dance, North Dakota

Ingo Arndt / Prairie Rattlesnake (Crotalus viridis viridis) in defensive posture, South Dakota

Ingo Arndt / American Bison (Bison bison) herd, South Dakota

Ingo Arndt / Milky way over sandstone rock formations, Badlands National Park, South Dakota

Ingo Arndt / Sandstone rock formations, Badlands National Park, South Dakota

Ingo Arndt / Sandstone rock formations, Badlands National Park, South Dakota

Ingo Arndt / Sandstone rock formations, Badlands National Park, South Dakota

Ingo Arndt / Sandstone rock formations, Badlands National Park, South Dakota