Michio Hoshino / Alaska Moose (Alces alces gigas) bull charging, Alaska

Richard Du Toit / African Elephant (Loxodonta africana) bull chasing Hippopotamus (Hippopotamus amphibius) group, Kruger National Park, South Africa

Colin Monteath / Red Deer (Cervus elaphus) bulls running up hill in winter, Hustai National Park, Mongolia

Donald M. Jones / Timber Wolf (Canis lupus) group running down American Elk (Cervus elaphus nelsoni) bull, Yellowstone National Park, Wyoming

Donald M. Jones / Timber Wolf (Canis lupus) group running down American Elk (Cervus elaphus nelsoni) bull, Yellowstone National Park, Wyoming

Donald M. Jones / American Elk (Cervus elaphus nelsoni) bull running, western Montana

Michael Quinton / Alaska Moose (Alces alces gigas) young bull charges young Timber Wolf (Canis lupus), Teklanika River, Denali National Park and Preserve, Alaska

Michio Hoshino / Alaska Moose (Alces alces gigas) male charging across tundra, Alaska

Michael Quinton / Caribou (Rangifer tarandus) bull running down hill, Alaska

Pete Oxford / Domestic Cattle (Bos taurus) bull running at a hacienda in the Andes Mountains during the annual cattle round-up, Ecuador