Matthias Breiter / Polar Bear (Ursus maritimus) adult male charging opponent, Churchill, Manitoba, Canada

Fred Bavendam / Giant Nudibranch (Dendronotus iris) attacking a Tube-dwelling Anemone (Pachycerianthus fimbriatus), Vancouver Island, British Columbia, Canada. Sequence 4 of 5

Michio Hoshino / Polar Bear (Ursus maritimus) males fighting, Churchill, Manitoba, Canada

Yva Momatiuk & John Eastcott / Northern Gannet (Morus bassanus) pair aggressively defending their territory in breeding colony, summer, Newfoundland, Canada

Thomas Mangelsen / Polar Bear (Ursus maritimus) pair sparring, near Churchill, Manitoba, Canada

Flip Nicklin / Polar Bear (Ursus maritimus) near carcass with camp dogs surrounding it, Canada

Flip Nicklin / Polar Bear (Ursus maritimus) pair sparring, Churchill, Manitoba, Canada

Fred Bavendam / Giant Nudibranch (Dendronotus iris) attacking a Tube-dwelling Anemone (Pachycerianthus fimbriatus), Vancouver Island, British Columbia, Canada. Sequence 3 of 5

Flip Nicklin / Narwhal (Monodon monoceros) fighting males with crossed tusks, Baffin Island, Canada

Michio Hoshino / Polar Bear (Ursus maritimus) males fighting, Churchill, Manitoba, Canada

Michio Hoshino / Polar Bear (Ursus maritimus) males fighting, Churchill, Manitoba, Canada

Michio Hoshino / Polar Bear (Ursus maritimus) males fighting, Churchill, Manitoba, Canada

Michio Hoshino / Polar Bear (Ursus maritimus) males fighting, Churchill, Manitoba, Canada

Michio Hoshino / Polar Bear (Ursus maritimus) males fighting, Churchill, Manitoba, Canada

Michio Hoshino / Polar Bear (Ursus maritimus) males fighting, Churchill, Manitoba, Canada

Michio Hoshino / Polar Bear (Ursus maritimus) males fighting, Churchill, Manitoba, Canada

Flip Nicklin / Narwhal (Monodon monoceros) two males fighting, Baffin Island, Nunavut, Canada

Thomas Marent / Siamang (Symphalangus syndactylus) hanging in tree, Singapore Zoo, Singapore

Thomas Marent / Siamang (Symphalangus syndactylus) hanging in tree, Singapore Zoo, Singapore

Andrew Walmsley / Male Siamang gibbon (hylobates / Symphalangus syndactylus) vocalising, with throat pouch extended, Captive, New Zealand, Endangered species

Andrew Walmsley / Male Siamang gibbon (hylobates / Symphalangus syndactylus) vocalising, with throat pouch extended, Captive, New Zealand, Endangered species

Andrew Walmsley / Pair of Siamang gibbon (Hylobates / Symphalangus syndactylus) vocalising together, note the male's extended throat pouch, Captive, New Zealand, endangered species

Thomas Marent / Siamang (Symphalangus syndactylus) in rainforest canopy, Sumatra, Indonesia

Thomas Marent / Siamang (Symphalangus syndactylus) hanging in rainforest tree, Sumatra, Indonesia

Eric Baccega / Two Siamang Gibbons (Hylobates / Symphalangus syndactylus) calling, vocal pouches inflated, Endangered, captive, from SE Asia

ZSSD / Siamang (Hylobates syndactylus) is an arboreal, black furred gibbon native to the forests of Malaysia, Thailand, and Sumatra

Anup Shah / Siamang gibbon (Hylobates / Symphalangus syndactylus) male hanging from arm, captive, Endangered

Rod Williams / Siamang gibbon {Hylobates / Symphalangus syndactylus} young female feeding, captive, from Malaysia and Sumatra, Endangered

Konrad Wothe / Siamang (Symphalangus syndactylus) vocalizing with vocal pouch inflated, native to southeast Asia