Marie Read / Wood Ducks (Aix sponsa), females behave aggressively toward a male (second from right) that is trying to join them on a floating log, autumn, New York, USA, October.

Marie Read / Canada geese (Branta canadensis) two during territorial fight in early spring, Ithaca. New York, USA

Marie Read / American avocets (Recurvirostra americana) two during aggressive (territorial) encounter, Bear River Migratory Bird Refuge, Utah, USA, May.

Paul Hobson / Parrot snake (Leptophis ahaetulla) in aggressive pose with mouth open. Costa Rica.

Ingo Arndt / Blue Crab (Discoplax hirtipes) with claws raised in defensive / aggressive posture, endemic to Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Blue Crab (Discoplax hirtipes) with claws raised in defensive / aggressive posture, endemic to Christmas Island, Indian Ocean, Australian Territory

Krijn Trimbos / Great crested grebe (Podiceps cristatus) with head low to the water in aggressive display, The Netherlands. March.

Doug Perrine / Female Hawaiian monk seal (Monachus schauinslandi) defending her pup from two males, which are aggressive with each other, Molokai Island, Hawaii, USA.

Alex Hyde / Baboon Spider (Pterinochilus murinus) in aggressive posture, photographed on a white background. Captive, originating from Africa.

Shattil & Rozinski,Shattil & Rozinski / Black bear (Ursus americanus) cub climbing a fence, Minnesota, USA, May.

Denis-Huot,Denis-Huot / White-backed Vulture (Gyps Africanus) feeding, Masai-Mara Game Reserve, Kenya

Andy Rouse / African Lioness (Panthera leo) portrait, with aggressive expression because of cubs nearby Maasai Mara, Kenya, Africa

Konrad Wothe / Aggressive Mute swan (Cygnus olor) Upper Bavaria, Germany, Europe

Bence Mate / Keel billed toucan (Ramphastos sulfuratus) in aggressive encounter with Montezuma Oropendola (Psarocolius montezuma) in rain, Laguna del Lagarto, Santa Rita, Costa Rica. Front cover bookplate of the H...

Doug Perrine / Hawaiian monk seals (Monachus schauinslandi) aggressive male attacks a five and a half week pup, mother (right) approaches to intervene; Papaloa Beach, Kalaupapa, Molokai, Hawaii, USA

Anup Shah / Western chimpanzee (Pan troglodytes verus) female 'Fanle' aged 13 years and protecting her infant son 'Flanle' aged 3 years from an aggressive male, Bossou Forest, Mont Nimba, Guinea. January 2011.

Paul D Stewart / 1853 illustration of Gorilla, contemporary coloured copperplate engraving from 'Das Buch der Welt' John Weik, Stuttgart. The lowland Gorilla was first accurately described outside Africa by the missio...

Carol Walker / Wild horses / Mustangs, two stallions play fighting, Pryor Mountains, Montana, USA, July 2010

Sergey Gorshkov / African elephant charging (Loxodonta africana) female with young calf, Okavango Delta, Botswana

Nick Garbutt / Adult male Hippopotamuses (Hippopotamus amphibius) posturing in aggressive 'yawn' behaviour, Luangwa River, South Luangwa National Park, Zambia, November. Digital composite (two frames stitched togeth...

Terry Whittaker / 2020VISION / Stag beetle (Lucanus cervus) two males displaying aggressive behaviour on oak tree branch at woodland edge, Suffolk, UK, Controlled conditions, July

Andrew Parkinson / Whooper swan (Cygnus cygnus) adult aggressively chasing another, UK visitor between November and March. Lancashire, UK, October.

Anup Shah / Adolescent male Lions (Panthera leo) play fighting, Masai Mara National Reserve, Kenya, March

Andy Rouse / Lonnberg's / Subantarctic Skua (Stercoraius antarcticus lonnbergi) displaying aggressive behaviour, South Shetland Islands, Antarctica. (Non-ex)

Martin Dohrn / Three hyenas (Crocuta crocuta) approaching a resting lion (Panthera leo) at night. Topi Plain, Masai Mara, Kenya. Image taken using an infared camera with no artificial visible light, on location for...

Anup Shah / African Lion (Panthera leo) head portrait of juvenile male, showing teeth in aggressive display, Masai Mara National Reserve, Kenya. April

Bence Mate / Keel-billed Toucan (Ramphastos sulfuratus) in aggressive encounter with a Montezuma Oropendola (Psarocolius montezuma), Laguna del Lagarto, Santa Rita, Costa Rica

Gerrit Vyn / Ruddy Duck (Oxyura jamaicensis) male in breeding plumage performing a "bubbling display"which is used in both courtship and aggressive territorial encounters. The male holds its head and tail and 2 ro...

Graham Eaton / Spiny Spider Crab (Maja squinado) with claws raised in an aggressive posture, in a fast tide, Abersoch, Wales, UK, May.

Edwin Giesbers / Asiatic black / Moon bear (Ursus thibetanus) aggressive behaviour displayed between two individuals, captive; Isselburg zoo; Germany.

Jeff Rotman / Tiger shark (Galeocerdo cuvier) demonstrating aggressive behavior, Red Sea, Egypt

Edwin Giesbers / Head portrait of Sumatran tiger (Panthera tigris sumatrae) with face half cast in shadow, with aggressive expression, captive

Jeff Rotman / Diver holds 20 kilo Northern / American Lobster (Homarus americanus) with claws open, demonstrating aggressive behavior, New England, USA, North Atlantic Ocean. Model released Model released.

Wild Wonders of Europe / Geslin / Two Grey seals (Halichoerus grypus) aggressive behaviour, wind blowing sand, Donna Nook, Lincolnshire, UK, November 2008

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...

Andy Rouse / Mute swan (Cygnus olor) aggressive cob on water, Wiltshire, UK

Mark Bowler / Wood ant {Formica rufa} aggressive sequence

Mark Taylor / Border Collie-cross bitch, Bliss, snarling, looking aggressive.

Andrew Parkinson / Mute swan (Cygnus olor) territorial adult, aggressive display posture, Derbyshire, UK, March

Andy Rouse / Hippopotamus (Hippopotamus amphibius) showing aggressive behaviour, South Africa

Andy Rouse / Hippopotamus (Hippopotamus amphibius) aggressive posture, South Africa

Wild Wonders of Europe / Lesniewski / Alpine marmot (Marmota marmota) aggressive behaviour, Hohe Tauern National Park, Austria, July 2008

Charlie Hamilton James / Common kingfisher {Alcedo atthis} female (right) being aggressive to chicks, encouraging them to disperse, England

Anup Shah / Aggressive Leopard snarling (Panthera pardus) Masai Mara NR, Kenya

Anup Shah / Lappet faced vulture approaching carcass (Torgos tracheliotus) Masai Mara NR, Kenya

Owen Newman / Male Red kangaroos fighting {Macropus rufus} Sturt NP, New South Wales Australia

Doug Perrine / Humpback whale exhibiting peduncle throw {Megaptera novaeangliae} Hawaii, Pacific Ocean - taken under research permit #882 (Non-ex).

Hanne & Jens Eriksen / Antarctic skua aggressive display. South Georgia {Stercorarius antarcticus}

Richard Du Toit / African wild dogs {Lycaon pictus} playfighting. Savute, Chobe NP, Botswana.

Doug Perrine / Atlantic spotted dolphins aggressive interaction {Stenella frontalis} Bahamas, Caribbean, (Non-ex).

Anup Shah / Patas monkeys {Erythrocebus patas} fighting, Laikipia Plateau, Kenya.

Anup Shah / Male patas monkeys {Erythrocebus patas} wrestling. Laikipia plateau, Kenya.

Doug Perrine / Great white shark jawing at surface {Carcharodon carcharias} South Africa (Non-ex).

Doug Perrine / Humpback whale exhibiting peduncle throw {Megaptera novaeangliae} Hawaii Pacific Ocean - taken under research permit #882 (Non-ex).

Karl Ammann / Chimpanzee aggressive behaviour

John Cancalosi / Great skua pair, aggressive display, Shetland Islands, Scotland.

Anup Shah / Face portrait of snarling Bengal tiger {Panthera tigris tigris} India

Anup Shah / Male tigers snarling {Panthera tigris tigris} Ranthambhore NP India Rajasthan

Anup Shah / Male Common zebras showing aggression {Equus quagga} Masai Mara NR, Kenya

Peter Bassett / Aggressive bull elephant seal and penguins on beach at St Andrews Bay, South Georgia

Tony Heald / Hippopotamus (Hippopotamus amphibius), aggressive with mouth open, in water. Mana Pools National Park, Zimbabwe.

David Tipling / Great tit (Parus major) two on log in pond, one in aggressive posture, in garden, Norfolk, England, UK. February

David Tipling / Blackbird (Turdus merula) male showing aggressive behaviour towards Great tit (Parus major) on log in pond, in garden, Norfolk, England, UK. February

Marie Read / Crested caracaras (Caracara cheriway), midair aggressive interaction between two for access to perch, Martin Refuge, Rio Grande Valley, Texas, USA, March.

Stefan Christmann / Adelie penguin (Pygoscelis adeliae) aggressive interaction with Emperor penguin (Aptenodytes forsteri) and chick, Atka Bay, Queen Maud Land, Antarctica.

Stefan Christmann / Adelie penguin (Pygoscelis adeliae) aggressive interaction with Emperor penguin (Aptenodytes forsteri) and chick, Atka Bay, Queen Maud Land, Antarctica.

Remi Masson / Great blue spotted mudskipper (Boleophthalmus pectinirostris) in aggressive pose, on mud at low tide. Kyushu Island, Japan. August.

Remi Masson / Great blue spotted mudskipper (Boleophthalmus pectinirostris) with mouth open in aggressive pose, on mud at low tide. Kyushu Island, Japan. August.

Nick Upton / Common / Eurasian crane (Grus grus) pair 'Monty' and 'Sedge' with their young chick, being mobbed by an aggressive Avocet (Recurvirostra avosetta) for approaching too close to its nest...

Nick Upton / John Field releasing a very large male White-clawed crayfish (Austropotamobius pallipes) back to a well-stocked stream where it was caught in case it proved too aggressive for safe translocation to an...

David Tipling / Eurasian black vulture (Aegypius monachus) in aggressive posture approaching food and other vultures Sierra San Pedro, Extremadura, Spain. December

David Tipling / Eurasian black vulture (Aegypius monachus) in aggressive posture approaching food and other vultures Sierra San Pedro, Extremadura, Spain. December

David Tipling / Eurasian black vulture (Aegypius monachus) in aggressive posture approaching food and other vultures Sierra San Pedro, Extremadura, Spain. December

David Tipling / Hooded crows (Corvus cornix) fighting, Hortobagy National Park, Hungary January

David Tipling / Hooded crow (Corvus cornix) fighting Hortobagy National Park, Hungary January

Eric Medard / Goosander (Mergus merganser) in aggressive pose in water, Switzerland. February.

David Pattyn / Mute swan (Cygnus olor) on a misty morning, with wings raised up in aggressive stance, Valkenhorst Nature Reserve, Valkenswaard, the Netherlands. December

Eric Baccega / African lion (Panthera leo) male in front of charging Cape buffalo herd (Syncerus caffer caffer), Masai Mara National Reserve, Kenya. Sequence 6 of 13. The lion along with a lioness had killed a buffa...

Eric Baccega / African lion (Panthera leo) male in front of charging Cape buffalo herd (Syncerus caffer caffer), Masai Mara National Reserve, Kenya. Sequence 5 of 13. The lion along with a lioness had killed a buffa...

Eric Baccega / African lion (Panthera leo) male in front of charging Cape buffalo herd (Syncerus caffer caffer), Masai Mara National Reserve, Kenya. Sequence 4 of 13. The lion along with a lioness had killed a buffa...

Emanuele Biggi / Young African elephant (Loxodonta Africana) with ears spread in aggressive posture Etosha National Park, Namibia

Denis-Huot / Lion (Panthera leo), aggressive lioness refusing to mate, Masai-Mara Game Reserve, Kenya

Denis-Huot / Lion (Panthera leo), aggressive lioness refusing to mate, Masai-Mara Game Reserve, Kenya

Denis-Huot / Lion (Panthera leo), aggressive lioness refusing to mate, Masai-Mara Game Reserve, Kenya

Denis-Huot / Lion (Panthera leo), aggressive lioness refusing to mate, Masai-Mara Game Reserve, Kenya

Nick Upton / Egyptian goose (Alopochen aegyptiacus) in an aggressive head down challenge to another goose on the margins of Rutland Water reservoir, Rutland, UK, August.

Nick Upton / Egyptian goose (Alopochen aegyptiacus) flapping its wings and calling in an aggressive challenge on the margins of Rutland Water reservoir, Rutland, UK, August.

Jochen Gerlach/ BIA / White-tailed Eagle (Haliaeetus albicilla) in aggressive display, Lodz, Poland

Mathias Schaef/ BIA / White-tailed Eagle (Haliaeetus albicilla) juvenile in aggressive display, Lodz, Poland

Jeff Foott / Dead trees killed by Mountain pine beetle (Dendroctonus ponderosae) Idaho, USA, August. The current outbreak of mountain pine beetles has been particularly aggressive. This is due to climate change,...

Jeff Foott / Dead 'beetle kill' trees burning in control fire in cleared camp ground. Rocky Mountain National Park, Colorado, USA, January. The current outbreak of mountain pine beetles has been particularly aggre...

Jeff Foott / Dead White bark pine trees (Pinus albicaulis) killed by Mountain pine beetle (Dendroctonus ponderosae) Grand Teton National Forest, Wyoming, USA. December. The current outbreak of mountain pine beetl...

Jeff Foott / Information sign about Mountain pine beetle sign. Rocky Mountain National Park, USA, October. The current outbreak of mountain pine beetles has been particularly aggressive. This is due to climate c...