Wild Wonders of Europe / Widstrand / Ganado bravo, fighting bull portrait, Ciudad Rodrigo, Salamanca Region, Castilla y Leon, Spain

Christophe Courteau / Two African Buffalo {Sincerus caffer} bulls sparring, Okavango Delta, Botswana.

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, a traditionally dressed 'cavalheiro' delivers the 'banderilla' mounted on his Lusitano stallion in the bullring...

Ben Osborne / African elephants (Loxodonta africana) bulls crowd into an emptying waterhole to drink, Savuti, Botswana. Taken on location for BBC Planet Earth series, 2005

Steven Kazlowski / Walrus (Odobenus rosmarus) two young bulls, in waters along Spitsbergen and the northwestern coast of the Svalbard Archipelago, Norway, Arctic Ocean, July

Juan Carlos Munoz / Granite feeding troughs for bulls in Sierra de Andujar Natural Park, Jaen, Andalusia, Spain, Jan 2010

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

Charlie Summers / African Elephant (Loxodonta africana) bulls in dominance fight, Mono Pools national Park, Zimbabwe, Southern Africa

Inaki Relanzon / Boy riding a bull, Inle Lake, Shan State, Myanmar, Burma. August 2009

Patricio Robles Gil / Matador in final stages of bullfight leaps over bull to pierce bull between horns with blade, Plaza de Toros, Mexico City, Mexico Sequence

Eric Baccega / Two Elk (Cervus canadensis) bulls at sunset, Jasper National Park, Rocky Mountains, Alberta, Canada, September

Wild Wonders of Europe / Geslin / Grey seal (Halichoerus grypus) bulls fighting covered in mud, Donna Nook, Lincolnshire, UK, November 2008

Michio Hoshino / Alaska Moose (Alces alces gigas) bulls fighting, Alaska

Suzi Eszterhas / Blue Wildebeest (Connochaetes taurinus) bulls fighting, Masai Mara, Kenya

Tony Heald / African elephant {Loxodonta africana} bulls walking in line, Etosha national park, Namibia.

Rolf Nussbaumer / Elk {Cervus elaphus} bulls fighting, Yellowstone NP, Wyoming, USA

Anup Shah / Two African elephant bulls establish dominance with ritual trial of strength Masai Mara NR Kenya

Gerry Ellis / African Elephant (Loxodonta africana) bulls engaged in greeting ritual, Amboseli National Park, Kenya

Gerry Ellis / African Elephant (Loxodonta africana) young bulls engage in greeting ritual, Amboseli National Park, Kenya

Michio Hoshino / Caribou (Rangifer tarandus) pair of bulls, Alaska

Tui De Roy / Atlantic Walrus (Odobenus rosmarus rosmarus) bachelor bulls on ice floe, North Coast Spitsbergen, Svalbard, Norwegian Arctic

Ann & Steve Toon / African elephants (Loxodonta africana) two bulls sparring at the waterhole in front of the lodge, Ol Donyo Wuas, Mbirikani Group Ranch, Amboseli-Tsavo ecosystem, Chyulu Hills, Kenya

Ben Hall / Greater kudu (Tragelaphus strepsiceros) male, silhouetted on cliff edge at dusk with storm clouds overhead, The Karoo, South Africa, Highly honoured, Windland Smith Rice / Nature's Best Awards competi...

Neil Aldridge / Waterbuck (Kobus ellipsiprymnus ellipsiprymnus) young bull lying down, Kruger National Park, South Africa

Jabruson / African Forest elephant (Loxodonta africana cyclotis) bulls sparring in poor evening light. Elephants visit the forest clearings to obtain valuable minerals located at certain points within the clear...

Jabruson / African Forest elephants (Loxodonta africana cyclotis) two bulls sparring after meeting in Dzanga bai clearing, Dzanga-Ndoki National Park, Central African Republic.

Jabruson / African Forest elephant (Loxodonta africana cyclotis) two bulls sparring, competition for access to valuable minerals located at certain points within the clearing's water points, Dzanga-Ndoki Nationa...

Jabruson / African Forest elephant (Loxodonta africana cyclotis) two bulls sparring, competition for access to valuable minerals located at certain points within the clearing's water points, Dzanga-Ndoki Nationa...

Jabruson / African Forest elephant (Loxodonta africana cyclotis) two bulls sparring, competition for access to valuable minerals located at certain points within the clearing's water points, Dzanga-Ndoki Nationa...

Jabruson / African Forest elephant (Loxodonta africana cyclotis) two bulls sparring, competition for access to valuable minerals located at certain points within the clearing's water points, Dzanga-Ndoki Nationa...

Jabruson / African Forest elephant (Loxodonta africana cyclotis) two bulls sparring, competition for access to valuable minerals located at certain points within the clearing's water points, Dzanga-Ndoki Nationa...

Jabruson / African Forest elephant (Loxodonta africana cyclotis) two bulls sparring, competition for access to valuable minerals located at certain points within the clearing's water points, Dzanga-Ndoki Nationa...

Jabruson / African Forest elephant (Loxodonta africana cyclotis) two bulls sparring, competition for access to valuable minerals located at certain points within the clearing's water points, Dzanga-Ndoki Nationa...

Jabruson / African Forest elephant (Loxodonta africana cyclotis) two bulls sparring, competition for access to valuable minerals located at certain points within the clearing's water points, Dzanga-Ndoki Nationa...

Jabruson / African Forest elephant (Loxodonta africana cyclotis) adult bull chasing others and vying for position at mineral drinking hole. These elephants visit the forest clearings to obtain valuable minerals...

Jabruson / African Forest elephant (Loxodonta africana cyclotis) bulls sparing, blurred motion, Dzanga-Ndoki National Park, Central African Republic

Jabruson / African Forest elephant (Loxodonta africana cyclotis) bulls sparing, blurred motion, Dzanga-Ndoki National Park, Central African Republic

Jabruson / African Forest elephant (Loxodonta africana cyclotis) bulls sparing, blurred motion, Dzanga-Ndoki National Park, Central African Republic

Wild Wonders of Europe / Widstrand / Ganado bravo, fighting bull profile, Ciudad Rodrigo, Salamanca Region, Castilla y Leon, Spain

Wild Wonders of Europe / Widstrand / Heck cattle (Bos taurus) auroch relative, walking profile, Oostvaardersplassen Nature Reserve, part of European Rewilding Area Network, The Netherlands

Paul D Stewart / Moose (Alces alces) bull resting by water. Grand Teton, Wyoming, USA, September.

Ann & Steve Toon / Nyala (Tragelaphus angasii), bulls lateral presentation display, Mkhuze Game Reserve, South Africa

Flip Nicklin / Southern Elephant Seal (Mirounga leonina) juvenile bulls fighting, South Georgia Island

Sharon Heald / African elephants (Loxodonta africana) two old bulls at a waterhole, Etosha National Park, Namibia October

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) bulls fighting, Kruger National Park, South Africa

Richard Du Toit / African Elephant (Loxodonta africana) bulls seen through car windows, Kruger National Park, South Africa

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

Donald M. Jones / Elk (Cervus elaphus) bulls, National Bison Range, Moise, Montana

Donald M. Jones / Elk (Cervus elaphus) bulls sparring, Jasper National Park, Alberta, Canada

Donald M. Jones / American Bison (Bison bison) bulls fighting, National Bison Range, Moise, Montana

Donald M. Jones / American Bison (Bison bison) bulls fighting, National Bison Range, Moise, Montana

Mark Raycroft / Caribou (Rangifer tarandus) bulls shedding velvet, North America

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, a traditionally dressed 'cavalheiro' mounted on his Lusitano stallion is chased by the bull, in the bullring of...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, a traditionally dressed 'cavalheiro' delivers the 'banderilla' mounted on his Lusitano stallion in the bullring...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, a traditionally dressed 'cavalheiro' delivers the 'banderilla' mounted on his Lusitano stallion in the bullring...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, traditionally dressed cowboys, mounted on their horses, drive the bulls through the streets of Vila Franca de Xi...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, traditionally dressed cowboys, mounted on their horses, drive the bulls through the streets of Vila Franca de Xi...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, traditionally dressed cowboys, mounted on their horses, drive the bulls in front of the bullring of Vila Franca...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, traditionally dressed cowboys, mounted on their horses, drive the bulls in front of the bullring of Vila Franca...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, traditionally dressed cowboys, mounted on their horses, drive the bulls through the streets of Vila Franca de Xi...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, traditionally dressed cowboys, mounted on their horses, drive the bulls through the streets of Vila Franca de Xi...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, traditionally dressed cowboys, mounted on their horses, drive the bulls in front of the bullring of Vila Franca...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, traditionally dressed cowboys, mounted on their horse, drive the bulls in front of the bullring of Vila Franca d...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, traditionally dressed cowboys, mounted on their horses, drive the bulls through the streets of Vila Franca de Xi...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, traditionally dressed cowboys, mounted on their horses, drive the bulls through the streets of Vila Franca de Xi...

Kristel Richard / During the Festa do Colete Encarnado (Red Waistcoat Festival), a bull running festival, traditionally dressed cowboys, mounted on their horses, drive the bulls through the streets of Vila Franca de Xi...

Theo Allofs / African Elephant (Loxodonta africana) young bulls playing, Skeleton Coast, Namib Desert, Namibia

Theo Allofs / African Elephant (Loxodonta africana) young bulls playing, Skeleton Coast, Namib Desert, Namibia

Theo Allofs / African Elephant (Loxodonta africana) young bulls playing, Skeleton Coast, Namib Desert, Namibia

Ben Osborne / African elephant (Loxodonta africana) bulls drinking at a waterhole, Savuti, Northern Botswana. Taken on location for BBC Planet Earth series, 2005

Steven Kazlowski / Walrus (Odobenus rosmarus) herd of bulls resting on a beach along the northwestern coast of Spitsbergen and the Svalbard Archipelago, Norway, Arctic Ocean, July

Steven Kazlowski / Walrus (Odobenus rosmarus) herd of bulls resting on a beach along the northwestern coast of Spitsbergen and the Svalbard Archipelago, Norway, Arctic Ocean, July

Steven Kazlowski / Walrus (Odobenus rosmarus) herd of bulls resting on a beach along the northwestern coast of Spitsbergen and the Svalbard Archipelago, Norway, Arctic Ocean, July

Richard Du Toit / African Elephant (Loxodonta africana) bulls sparring, Kruger National Park, South Africa

ZSSD / African Elephant (Loxodonta africana) bulls sparring, native to Africa

ZSSD / African Elephant (Loxodonta africana) bulls sparring, native to Africa

Donald M. Jones / American Elk (Cervus elaphus nelsoni) bulls sparring, western Alberta, Canada

Donald M. Jones / American Elk (Cervus elaphus nelsoni) bulls sparring, western Alberta, Canada

Donald M. Jones / American Elk (Cervus elaphus nelsoni) bulls sparring, western Alberta, Canada

Donald M. Jones / American Elk (Cervus elaphus nelsoni) bulls sparring, western Alberta, Canada

Donald M. Jones / American Elk (Cervus elaphus nelsoni) bulls sparring, western Alberta, Canada

Donald M. Jones / American Elk (Cervus elaphus nelsoni) bulls, western Alberta, Canada

Juan Carlos Munoz / Granite feeding troughs for bulls in Sierra de Andujar Natural Park, Jaen, Andalusia, Spain, Jan 2010

Suzi Eszterhas / Sumatran Forest Elephant (Elephas maximus sumatranus) bulls play fighting in water, Way Kambas Elephant Training Center, Sumatra, Indonesia

Pete Oxford / Southern Elephant Seal (Mirounga leonina) bulls fighting, Sea Lion Island, Falkland Islands

Charlie Summers / American Bison (Bison bison) close-up of two Bulls shoving and butting in dominance behaviour, Custer State Park of South Dakota, USA

Mark Raycroft / Alaska Moose (Alces alces gigas) bulls sparring in tundra, Alaska

Mark Raycroft / Alaska Moose (Alces alces gigas) bulls sparring in tundra, Alaska

Doug Wechsler / Beach with group of dead trees (boneyard), due to natural coastal erosion. Bulls Island, South Carolina, USA. April 2010

Doug Wechsler / Beach with group of dead trees (boneyard), due to natural coastal erosion. Bulls Island, South Carolina, USA. 2010

Winfried Wisniewski / Northern Elephant Seal (Mirounga angustirostris) young bulls sparring on beach, San Simeon, California

Winfried Wisniewski / Northern Elephant Seal (Mirounga angustirostris) young bulls sparring on beach, San Simeon, California

Winfried Wisniewski / Northern Elephant Seal (Mirounga angustirostris) young bulls sparring in surf, San Simeon, California

Steven Kazlowski / Walruses (Odobenus rosmarus) bulls of various ages resting together on sandspit, along the coast of Svalbard, Atlantic coast.

Gerry Ellis / African Elephant (Loxodonta africana) bulls greeting ritual, Amboseli National Park, Kenya

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