Nick Garbutt / American bison (Bison bison) female covered in hoar frost near hot spring, portrait. Midway Geyser Basin, Yellowstone National Park, USA. February.

Jack Dykinga / Bighorm sheep (Ovis canadensis) males grouped together before the rutting season. Valley of Fire State Park, Nevada, USA, February.

David Pattyn / Alpine ibex (Capra ibex) adult males fighting in alpine landscape, Valsavarenche, Gran Paradiso National Park, Aosta Valley, Italy, May

David Pattyn / Alpine Ibex (Capra ibex) in its landscape, Valsavarenche, Gran Paradiso national park, Aosta Valley, Italy, May

David Pattyn / Alpine ibex (Capra ibex) struggling in deep snow on a steep slope, Valsavarenche, Gran Paradiso National Park, Aosta Valley, Italy, January

Eric Baccega / Female Uganda kob (Kobus kob thomasi) suckling calf. Murchisson Falls National Park, Uganda. February.

Jed Weingarten / Wild Wonders of China / Takin (Budorcas taxicolor) Tangjiahe Nature Reserve, Sichuan Province, China. April.

Jed Weingarten / Wild Wonders of China / Snow leopard (Uncia uncia) with Bharal (Pseudois nayaur) prey, Serxu County, Garze Prefecture, Sichuan Province, China.

Anup Shah / Mixed herd of Common or Plains zebra (Equus quagga burchellii) and Eastern white-bearded wildebeest (Connochaetes taurinus) - remote camera. Masai Mara National Reserve, Kenya.

Donald M. Jones / Bighorn Sheep (Ovis canadensis) ram, Montana

Donald M. Jones / Bighorn Sheep (Ovis canadensis) ram, Montana

Donald M. Jones / Bighorn Sheep (Ovis canadensis) female and male in winter, Jasper National Park, Alberta, Canada

Donald M. Jones / Bighorn Sheep (Ovis canadensis) females in winter, Jasper National Park, Alberta, Canada

Donald M. Jones / American Bison (Bison bison) dust bathing, National Bison Range, Montana

Ann & Steve Toon / Impala (Aepyceros melampus) allo-grooming, iMfolozi game reserve, KwaZulu-Natal, South Africa, August

Loic Poidevin / Alpine ibex (Capra ibex) female, Jura, Switzerland, September.

Suzi Eszterhas / African Lion (Panthera leo) young male feeding on Cape Buffalo (Syncerus caffer) prey, Sabi Sands Private Game Reserve, South Africa

Nick Garbutt / RF - Skull of a male Himalayan ibex (Capra sibirica) (killed by a snow leopard) lying on steep rocky slope. Himalayas, Ladakh, northern India. (This image may be licensed either as rights managed or r...

Nick Garbutt / Male American Bison (Bison bison) walking through snow. Firehole River Valley, Yellowstone National Park, Wyoming, USA. January

Richard Du Toit / Impala (Aepyceros melampus) males fighting, Mkhuze Game Reserve, KwaZulu-Natal, South Africa

Sandesh Kadur / Blue wildebeest (Connochaetes taurinus) crossing a river, Serengeti National Park, Tanzania.

Stephane Granzotto / Alpine ibex (Capra ibex) feeding in deep snow, digging to reach food, Rhone-Alpes, France, December.

Staffan Widstrand / Wild Wonders of China / Sichuan / Tibetan takin (Budorcas taxicolor tibetana) walking through a forest in Tangjiahe National Nature Reserve,Qingchuan County, Sichuan province, China

Donald M. Jones / Minden / Bighorn Sheep (Ovis canadensis) ram, western Canada

Ann & Steve Toon / Springbok (Antidorcas marsupialis) herd fleeing predator, Kgalagadi Transfrontier Park, South Africa.

Guy Edwardes / Red-billed oxpecker (Buphagus erythrorhynchus) feeding on Impala (Aepyceros melampus), Savuti, Botswana.

Winfried Wisniewski / Cape Buffalo (Syncerus caffer) drinking at waterhole at night, KwaZulu-Natal, South Africa

Sebastian Kennerknecht / Leopard (Panthera pardus) female feeding on sub-adult male Impala (Aepyceros melampus) prey in tree, Greater Makalali Private Game Reserve, South Africa

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) bull browsing in winter, Yellowstone National Park, Wyoming

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

Sebastian Kennerknecht / American Bison (Bison bison) female in winter, Yellowstone National Park, Wyoming

Sebastian Kennerknecht / American Bison (Bison bison) female covered with frost in winter, Yellowstone National Park, Montana

Sebastian Kennerknecht / American Bison (Bison bison) female in snow, Riding Mountain National Park, Manitoba, Canada

Jim Manthorpe / American bison (Bison bison) feeding, Yellowstone National Park, Wyoming, USA, August.

Jaymi Heimbuch / Yellow-billed Oxpecker (Buphagus africanus) picking parasites off of Cape Buffalo (Syncerus caffer), Masai Mara, Kenya

Donald M. Jones / Dall's Sheep (Ovis dalli) ram, Denali National Park, Alaska

Donald M. Jones / Bighorn Sheep (Ovis canadensis) ram, western Montana

Donald M. Jones / Bighorn Sheep (Ovis canadensis) ram, western Montana

Donald M. Jones / Bighorn Sheep (Ovis canadensis) ewe and ram, western Montana

Donald M. Jones / American Bison (Bison bison) bull, National Bison Range, Montana

Donald M. Jones / American Bison (Bison bison) with grass on horns, National Bison Range, Montana

Donald M. Jones / American Bison (Bison bison) bull, National Bison Range, Montana

Donald M. Jones / American Bison (Bison bison) bull, National Bison Range, Montana

Nick Garbutt / Urial sheep (Ovis vignei) herd running across steep barren slopes. Himalayas near Ulley, Ladakh, India.

Graeme Guy/ BIA / African Lion (Panthera leo) female suffocating Blue Wildebeest (Connochaetes taurinus) prey, Masai Mara, Kenya

Danny Green / RF - Bison (Bison bison) breathing in the cold air, Yellowstone National Park, USA, February (This image may be licensed either as rights managed or royalty free.)

Bence Mate / African buffalo (Syncerus caffer) at waterhole at night, Mkuze, South Africa Third place in the Nature Portfolio category of the World Press Photo Awards 2017.

Bence Mate / African buffalo (Syncerus caffer) and Warthog (Phacochoerus africanus) at night with full moon, Mkuze, South Africa Third place in the Nature Portfolio category of the World Press Photo Awards 2017.

Bence Mate / African buffalo (Syncerus caffer) at waterhole at night, Mkuze, South Africa Third place in the Nature Portfolio category of the World Press Photo Awards 2017.

Ann & Steve Toon / Impala (Aepyceros melampus) with redbilled oxpecker (Buphagus erythrorhynchus), Kruger National Park, South Africa.

Michael Quinton / Dall's Sheep (Ovis dalli) ram, lamb, and ewe, Yukon Territory, Canada

Francisco Marquez / Two male Iberian wild goats (Capra pyrenaica) fighting, Sierra de Gredos, Spain, November.

Philippe Clement / Group of Alpine ibex (Capra ibex) climbing a cliff face, with others fighting above them, Gran Paradiso National Park, Graian Alps, Italy, June.

Philippe Clement / Three male Alpine ibex (Capra ibex) climbing up a steep mountain rock face, one pushes another one away, Gran Paradiso National Park, Graian Alps, Italy, June.

Philippe Clement / Two male Alpine ibex (Capra ibex) fighting on a steep mountain rock face, Gran Paradiso National Park, Graian Alps, Italy, June.

Eric Baccega / Small herd of Muskox (Ovibos moschatus) feeding in a blizzard, Banks Island, Northwest Territories, Canada.

Ann & Steve Toon / RF - Leopard female (Panthera pardus) watched by two Gemsbok (Oryx gazella), Kgalagadi transfrontier park, South Africa, June. (This image may be licensed either as rights managed or royalty free.)

Danny Green / Bison (Bison bison) herd walking in line in snow, Yellowstone National Park, Wyoming, USA, February

Inaki Relanzon / Arabian Oryx (Oryx leucoryx) at sunset. Previously extinct in the wild, their conservation status is now stable thanks to conservation efforts.This male is part of a reintroduction program in Dubai, U...

Ann & Steve Toon / Common wildebeest (Connochaetes taurinus) with reflection at waterhole, Zimanga private game reserve, KwaZulu-Natal, South Africa, September

Ann & Steve Toon / Sable (Hippotragus niger), Chobe National Park, Botswana, June

Ann & Steve Toon / Cape buffalo (Syncerus caffer) at waterhole at night with plains zebra (Equus quagga), Zimanga private game reserve, KwaZulu-Natal, South Africa, September

Ann & Steve Toon / Cape buffalo (Syncerus caffer) drinking at waterhole at night, Zimanga private game reserve, KwaZulu-Natal, South Africa, September

Ann & Steve Toon / Cape buffalo (Syncerus caffer) drinking at waterhole at night, Zimanga private game reserve, KwaZulu-Natal, South Africa, September

Nick Garbutt / Herd of American bison (Bison bison) in snow, Yellowstone National Park, Wyoming, Yellowstone, January.

Richard Du Toit / Black Wildebeest (Connochaetes gnou), Rietvlei Nature Reserve, South Africa

Jim Brandenburg / American Bison (Bison bison) herd on prairie with quartz, Blue Mounds State Park, Minnesota

Denis-Huot / Blue wildebeest (Connochaetes taurinus), migrating herd silhouetted on the horizon at sunset, Masai Mara Game Reserve, Kenya

David Pattyn / Chamois (Rupicapra rupicapra) in deep snow, Gran Paradiso National Park, Italy. November. Commended in the Asferico Photography Competition 2016.

Sergey Gorshkov / Lionesses (Panthera leo) trying to bring down African buffalo (Syncerus caffer) Londolozi Private Game Reserve, Sabi Sands Game Reserve, South Africa. Sequence 1 of 5

Sergey Gorshkov / Lionesses (Panthera leo) trying to bring down African buffalo (Syncerus caffer) Londolozi Private Game Reserve, Sabi Sands Game Reserve, South Africa. Sequence 2 of 5

Sergey Gorshkov / Lionesses (Panthera leo) trying to bring down African buffalo (Syncerus caffer) Londolozi Private Game Reserve, Sabi Sands Game Reserve, South Africa. Sequence 3 of 5

Sergey Gorshkov / Lioness (Panthera leo) trying to bring down African buffalo (Syncerus caffer) Londolozi Private Game Reserve, Sabi Sands Game Reserve, South Africa. Sequence 4 of 5

Sergey Gorshkov / Lionesses (Panthera leo) trying to bring down African buffalo (Syncerus caffer) Londolozi Private Game Reserve, Sabi Sand Game Reserve, South Africa. Sequence 5 of 5

Neil Aldridge / Yellow-billed oxpecker (Buphagus africanus) perched on the back of an African buffalo (Syncerus caffer) on the banks of the Chobe River, Chobe National Park, Botswana.

Neil Aldridge / Steenbok (Raphicerus campestris) female standing framed by a fallen tree, Mapungubwe National Park, Limpopo Province, South Africa.

Neil Aldridge / Sable antelope (Hippotragus niger) bull charging through the shallows of the Selinda Spillway, with another behind, northern Botswana, August.

Neil Aldridge / Red lechwe (Kobus leche) standing on an island, Zibadianja Lagoon, Selinda Reserve, northern Botswana.

Neil Aldridge / Two Impalas (Aepyceros melampus) ewes grooming each other in evening light on South Africa's Kruger National Park.

Neil Aldridge / Eland (Tragelaphus derbianus) male in evening light, Kariega Game Reserve, South Africa

Neil Aldridge / African buffalo (Syncerus caffer) standing on the banks of the Chobe River, Chobe National Park, Botswana.

Neil Aldridge / Mud-covered face of bull African buffalo (Syncerus caffer) with a cateract in one eye, on the banks of the Chobe River, Chobe National Park, Botswana.

Chris & Monique Fallows / Impala (Aepyceros melampus) herd at dawn, Mana Pools National Park, Zimbabwe, October.

Juan Carlos Munoz / Gemsbok (Oryx gazella) aerial view of herd on sand, Namib Desert, Namibia.

Juan Carlos Munoz / Gemsbok (Oryx gazella) aerial view of herd on sand, Namib Desert, Namibia.

Wim van den Heever / Cheetah (Acinonyx jubatus) hunting Springbok (Antidorcas marsupialis) trying to trip up the prey, Kgalagadi, South Africa

Wim van den Heever / Two Cheetah (Acinonyx jubatus) chasing Springbok (Antidorcas marsupialis) Kgalagadi, South Africa

Wim van den Heever / Oryx (Oryx gazella) lone animal standing on the top of a red dune, Sossuvlei, Namibia.

Wim van den Heever / Cheetah (Acinonyx jubatus) hunting Springbok (Antidorcas marsupialis) Kgalagadi, South Africa

David Pattyn / Alpine ibex (Capra ibex) on a mountain side in autumn with European larch tree (Larix decidua) trees in the back the Alps, Gran Paradiso National Park, Italy. November.

Matthias Breiter / American Bison (Bison bison) herd grazing, Grand Teton National Park, Wyoming

Richard Du Toit / Cape Buffalo (Syncerus caffer) herd chasing away Cheetah (Acinonyx jubatus), Rietvlei Nature Reserve, South Africa

Ingo Arndt / African Lion (Panthera leo) female feeding on Blue Wildebeest (Connochaetes taurinus) kill, Masai Mara, Kenya

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