Sebastian Kennerknecht / American Bison (Bison bison) herd grazing in winter, Gardiner, Yellowstone National Park, Montana

Sebastian Kennerknecht / American Bison (Bison bison) herd grazing in winter, Gardiner, Yellowstone National Park, Montana

Sebastian Kennerknecht / American Bison (Bison bison) female cleaning nose with tongue, Yellowstone National Park, Wyoming

Sean Crane / American Bison (Bison bison) mother and calf at sunrise, Yellowstone National Park, Wyoming

Suzi Eszterhas / American Bison (Bison bison) cow and calf playing, Yellowstone National Park, Montana

Shin Yoshino / American Bison (Bison bison) two males fighting, Yellowstone National Park, Wyoming

Ralf Kistowski/ BIA / Coyote (Canis latrans) in winter, Yellowstone National Park, Wyoming

Jeff Foott / Elk (Cervus elaphus) bull, Yellowstone National Park, Wyoming

Jeff Foott / American Bison (Bison bison) drinking in frost-covered meadow, Yellowstone National Park, Wyoming

Jeff Foott / American Bison (Bison bison) in frost-covered meadow, Yellowstone National Park, Wyoming

Jeff Foott / American Bison (Bison bison) in frost-covered meadow, Yellowstone National Park, Wyoming

Jeff Foott / American Bison (Bison bison) in frost-covered meadow, Yellowstone National Park, Wyoming