Wild Wonders of Europe / Widstrand / Eurasian brown bear (Ursus arctos) cubs fighting while playing, Suomussalmi, Finland, July 2008

Wild Wonders of Europe / Widstrand / Two Eurasian brown bear (Ursus arctos) cubs fighting, Suomussalmi, Finland, July 2008

Wild Wonders of Europe / Lesniewski / Alpine marmots (Marmota marmota) playing, Hohe Tauern National Park, Austria, July 2008

Wild Wonders of Europe / Widstrand / Eurasian brown bear (Ursus arctos) cubs fighting while playing, Suomussalmi, Finland, July 2008

Fiona Rogers / Ring-tailed Lemur (Lemur catta) infant (less than 1 month) chasing tail of adult lemur. Berenty Private Reserve, Madagascar. Oct 2008.

Andy Rouse / Asian elephant (Elaphus maximus) two young calves playing, Minneria NP, Sri Lanka

Bernard Castelein / Southern plains grey / Hanuman langur {Semnopithecus dussumieri} family group on rock, Rajasthan, India

Niall Benvie / Why biodiversity matters. Person pulling labelled wooden block from game of Jenga, all blocks above will come tumbling down, Scotland, UK, 2007

Bruno D'Amicis / Young Barbary Macaque (Macaca sylvanus) playing among Cedar (Cedrus atlantica) trees, backlit, Endangered species. Atlas mountains, Morocco, NW Africa

Bruno D'Amicis / Young Barbary Macaques (Macaca sylvanus) playing among Cedar (Cedrus atlantica) trees, backlit, Endangered species. Atlas mountains, Morocco, NW Africa

Petra Wegner / Cavalier King Charles Spaniel, blenheim, retrieving ball, running on beach

Petra Wegner / Cavalier King Charles Spaniel, puppy, 14 weeks, ruby, running on beach with adult in background

Andrew Parkinson / Grey seal {Halichoerus grypus} two adolescents play-fighting among the breaking waves, Lincolnshire, UK

Oriol Alamany / Stoat / Ermine (Mustela erminea) two juveniles playing, Aran valley, Pyrenees, Spain

Andrew Parkinson / Grey seal {Halichoerus grypus} two adolescents play-fighting among the breaking waves, Lincolnshire, UK

Bernard Castelein / Grey seal (Halichoerus grypus) yawning on beach, Helgoland, Germany. Second Place in the Comedy Award of the Terre Sauvage Nature Images Awards 2016.

Bernard Castelein / Grey Seal (Halichoerus grypus) covering face with flippers, Helgoland, Germany

Bernard Castelein / Young grey seal (Halichoerus grypus) lying on sand, Helgoland, Germany

Yukihiro Fukuda / Japanese macaque / Snow monkey {Macaca fuscata} young monkeys playing in trees, Jigokudani, Nagano, Japan

Yukihiro Fukuda / Japanese macaque / Snow monkey {Macaca fuscata} young monkeys playing in the sunshine in the trees, Jigokudani, Nagano, Japan

Jane Burton / A playful tabby kitten pouncing on a West Highland White Terrier puppy as he pokes his head out from a Father Christmas hat.

Jane Burton / Silver tabby-and-white kitten, 8 weeks old, playing with Christmas tinsel.

Igor Shpilenok / Kamchatka brown bear (Ursus arctos beringianus) chasing each other beside water, Kronotsky Nature Reserve, Kamchatka, Far East Russia

Shattil & Rozinski / Red fox {Vulpes vulpes} cubs playing, Rocky Mt Arsenal NWR, Colorado, USA

Anup Shah / African lion {Panthera leo} lioness on guard while young cubs play on rock / kopje, Masai Mara GR, Kenya

Anup Shah / African lion {Panthera leo} young cub, two months old, playing with mother's tail, Masai Mara GR, Kenya

Anup Shah / African lion {Panthera leo} cub playing with sleeping lioness' ear, Masai Mara GR, Kenya

Pete Oxford / Galapagos sealions (Zalophus californianus wollebaeki) playing in shallow water, Gardner Bay, Española / Hood Is, Galapagos

Peter Scoones / Underwater view of African Elephants {Loxidonta africana} playing, Okavango Delta, Botswana photographed during making of BBC Planet Earth series 2005

Pete Cairns / Three boys playing in forest, Cairngorms National Park, Scotland, UK 2006 Model released.

Jane Burton / Tabby Domestic cat kitten {Felis catus} looking playful, UK

Anup Shah / Simien jackal / Ethiopian wolf {Canis simensis} cub playing with mother, Bale Mountains, Bale NP, Ethiopia

Anup Shah / African elephant babies playing (Loxodonta africana) Masai Mara, Kenya, Africa

DOC WHITE / Polar bear mother and cubs sliding down slope {Ursus maritimus} Canadian Arctic

Pete Cairns / Young boy peering around Birch tree, Cairngorms, Scotland, UK Model released.

Staffan Widstrand / Polar bear lying on back playing with twig {Ursus maritimus} Canada Churchill,

Anup Shah / Juvenile orang utan (Pongo abelii) swinging on liana over water Gunung Leuser NP Sumatra Indonesia

Anup Shah / Cheetah cubs playing together {Acinonyx jubatus} Masai Mara, Kenya. 'Frisky's' litter

Anup Shah / Juvenile orang utan (Pongo abelii) swinging on liana Gunung Leuser NP Sumatra Indonesia

Anup Shah / Juvenile orang utan (Pongo abelii) swinging on liana Gunung Leuser NP Sumatra Indonesia

Anup Shah / Juvenile orang utan (Pongo abelii) swinging on liana Gunung Leuser NP Sumatra Indonesia

Anup Shah / Olive baboon baby playing with adult's tail (Papio anubis) Masai Mara, Kenya, Africa

Anup Shah / Male lions playing (Panthera leo) Masai Mara, Kenya, East Africa. Homosexual?

Anup Shah / Inquisitive cheetahs with Bat eared fox, Masai Mara Kenya (Acinonyx jubatus)

Anup Shah / Orang utan playing with stick, (Pongo abelii) Gunung Leuser NP, Indonesia

Anup Shah / Orang utan playing with water in stream, (Pongo abelii) Gunung Leuser NP Indonesia

Anup Shah / Orang utan baby playing with stick, (Pongo abelii) Gunung Leuser NP, Indonesia

Anup Shah / Orang utan baby hanging upside down from branch, (Pongo abelii) Gunung Leuser NP, Indonesia

Suzi Eszterhas / Cheetah {Acinonyx jubatus} mother with 8-week cub climbing on her head, Masai Mara, Kenya.

Todd Pusser / Dusky dolphin doing backflip {Lagenorhynchus obscurus}, Kaikoura, New Zealand, Pacific

David Kjaer / Red fox females fighting {Vulpes vulpes} captive England

Todd Pusser / Dusky dolphin playing with kelp {Lagenorhynchus obscurus}, Kaikoura, New Zealand

Anup Shah / Young African lion cub climbing tree {Panthera leo} Masai Mara, Kenya

Anup Shah / Two young African lion cubs interacting {Panthera leo} Masai Mara, Kenya

Anup Shah / Young Chimpanzee chewing vine, 'Tom', Gombe NP, Tanzania 2002

Anup Shah / Leopard grooming cub {Panthera pardus}, Masai Mara Game Reserve, Kenya

Richard Du Toit / Two Subadult Cheetahs playing {Acinonyx jubatus} Sabi Sand GR South Africa. Cheetahs are the 100m gold medalists of the animal kingdom, capable of short sprints at 70mph. The human record is 27mph.

Peter Blackwell / Cheetah cubs, aged 6months, playing {Acinonyx jubatus} Masai mara NR, Kenya

Terry Andrewartha / Two Polar bears fighting {Ursus maritimus} Hudson Bay, Canada

Terry Andrewartha / Two Polar bears fighting {Ursus maritimus} Hudson Bay, Canada

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

Doug Perrine / Long beaked common dolphin leaping in bow wake of tanker {Delphinus capensis} Transkei, (Non-ex).

Doug Perrine / Atlantic spotted dolphins bowriding beneath boat {Stenella frontalis} Azores (Non-ex).

Anup Shah / Young Southern plains grey / Hanuman langur {Semnopithecus dussumieri} playing, Ranthambore NP, India

Anup Shah / Young Southern plains grey / Hanuman langur {Semnopithecus dussumieri} playing, Ranthambore NP, India

Doug Perrine / Wild sociable Bottlenose dolphin leaps in boat wake {Tursiops truncatus} Turks & (Non-ex).

Doug Perrine / Bottlenose dolphins jumping high above surface {Tursiops truncatus} Bahamas Caribbean (Non-ex).

Doug Perrine / Two Atlantic Bottlenose dolphins leaping {Tursiops truncatus} Bahamas - captive (Non-ex).

Doug Perrine / Two Bottlenose dolphins leaping above surface {Tursiops truncatus} Caribbean - captive (Non-ex).

Doug Perrine / Spinner dolphin leaping {Stenella longirostris} Kona, Hawaii, Pacific Ocean (Non-ex).

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

Doug Perrine / Atlantic spotted dolphins jumping {Stenella frontalis} Azores, Portugal, North Atlantic (Non-ex).

Doug Perrine / Atlantic spotted dolphins in mock combat {Stenella frontalis} Bahamas, Caribbean (Non-ex).

Peter Blackwell / Two young African elephants {Loxodonta africana} Amboseli NP, Kenya

Doug Perrine / Humpback whale mother and calf {Megaptera novaeangliae} Hawaii, USA Pacific Ocean - taken under research permit #633 (Non-ex).

Anup Shah / Olive baboon playing with baby {Papio anubis} Masai Mara, Kenya

Anup Shah / Cheetah cubs playing near mother {Acinonyx jubatus} Masai Mara, Kenya

Anup Shah / Cheetahs play fighting {Acinonyx jubatus} Masai Mara, Kenya

Anup Shah / Leopard cub playing with mother {Panthera pardus} Masai Mara, Kenya

Anup Shah / Cheetah cub playing with mother {Acinonyx jubatus} Masai Mara, Kenya

Anup Shah / Cheetahs cubs play fighting {Acinonyx jubatus} Masai Mara, Kenya

Anup Shah / Lion cub playing with mother's tail {Panthera leo} Masai Mara, Kenya

Anup Shah / Leopard cub playing with mother {Panthera pardus} Masai Mara, Kenya

Anup Shah / Leopard cub playing with mother {Panthera pardus} Masai Mara, Kenya

TJ Rich / One-week-old baby African elephant playing in sand between mother's legs {Loxodonta africana} Samburu NP, Kenya

Anup Shah / Chimpanzee baby watching adult playing with twig

Charlie Hamilton James / Simien jackal (Ethiopian wolf) with cubs. Sanetti plateau, Ethiopia

Bengt Lundberg / Great bustards vocalising {Otis tarda} East-Germany

Anup Shah / Lion cub (Panthera leo) giving invitation to play. Masai Mara, Kenya, East Africa

Anup Shah / Leopard cub (Panthera pardus) among rocks. Masai Mara, Kenya, East Africa

Anup Shah / Lion cubs playing Masai Mara Kenya

Anup Shah / Cheetah female + cub playing {Acinonyx jubatus} Masai Mara, Kenya. 'Frisky' with one of 3rd litter.

Anup Shah / Cheetah cubs playing together {Acinonyx jubatus} Masai Mara, Kenya. 'Frisky's' litter

Anup Shah / Cheetah cubs playing together {Acinonyx jubatus} Masai Mara, Kenya. 'Frisky's' litter

Anup Shah / Cheetah cubs playing together {Acinonyx jubatus} Masai Mara, Kenya. 'Frisky's' litter

Jeff Rotman / Bottlenose dolphin (Tursiops truncatus) plays with sea cucumber, Red Sea