Oscar Dewhurst / Grey squirrel (Sciurus carolinensis) stood upright on short grass. London, England, UK. March.

SCOTLAND: The Big Picture / Red squirrel (Sciurus vulgaris) male standing upright in alert pose,Cairngorms National Park, Highlands, Scotland, UK, May 2016.

SCOTLAND: The Big Picture / Red Squirrel (Sciurus vulgaris) standing upright in alert pose. Cairngorms National Park, Scotland, UK, March.

Nick Upton / European robin (Erithacus rubecula) standing upright in a territorial threat display in a meadow among patchy snow, Wiltshire, UK, January.

Shattil & Rozinski / Juvenile American black bear (Ursus americanus), brown phase, standing upright and leaning on a car, Denver, Colorado, USA, July.

Denis-Huot,Denis-Huot / Grizzly bears (Ursus arctos horribilis) looking for salmon, Brooks river, Katmai national park, Alaska, North America,

Tim Laman/Nat Geo Image Collection / Greater Bird of Paradise (Paradisaea apoda) male performing upright wing pose display, Badigaki Forest, Wokam Island in the Aru Islands, Indonesia.

Rolf Nussbaumer / Solitary bee, adult perched on Mexican hat (Ratibida columnifera) Dinero, Lake Corpus Christi, South Texas, USA.

Laurie Campbell / Common / Harbour Seal (Phoca vitulina) bottling / sleeping upright in water and moored in bed of sea thong weed, Islay, Scotland, April

Peter Cairns / 2020VISION / Old fishing boat held upright at low tide with ropes and chains, Roa Island, Morecambe Bay, Cumbria, England, UK, February 2012. Did you know? Over the last decade the number of UK fishermen has decl...

Andrew Parkinson / Red squirrel (Sciurus vulgaris) standing on its hind legs, Cairngorms National Park, Scotland, UK, March.

Andrew Parkinson / Red squirrel (Sciurus vulgaris) standing on its hind legs, Cairngorms National Park, Scotland, UK, March.

Diane McAllister / Coastal Brown bear (Ursus arctos horribilis) female and her cub standing in the long grass. She is looking warily at an approaching boar. Lake Clark National Park, Alaska, USA, July

Diane McAllister / Coastal Brown bear (Ursus arctos) female standing up and looking around while eating sedge grass in Lake Clark National Park. Alaska, USA, July

Visuals Unlimited / Brown Bear (Ursus arctos) standing, running, jumping

John Cancalosi / Golden-mantled ground squirrel (Spermophilus lateralis) with very full cheek pouches. Montana, USA, Oct 2010

Andrew Parkinson / Juvenile Rabbit (Oryctolagus cuniculus) head portrait, sitting upright near their warren. Norfolk, UK. June (non-ex)

Andrew Parkinson / Two juvenile Rabbits (Oryctolagus cuniculus) sitting upright near their warren. Norfolk, UK. June (non-ex)

Nick Upton / Ichneumon Wasp (Ichneumonidae) with antenna upright, on leaf. Wiltshire garden, UK, May.

Steven Kazlowski / Female Polar bear (Ursus maritimus) curiously checks out the photographer, standing upright on hind legs, Svalbard, Norway

Edwin Giesbers / Portrait of European otter (Lutra lutra) sitting upright in snow, captive, the Netherlands

Edwin Giesbers / Portrait of European otter (Lutra lutra) sitting upright in snow, captive, the Netherlands

Edwin Giesbers / Red squirrel (Sciurus vulgaris) sitting upright in deep snow, Austria, Europe

Edwin Giesbers / Red squirrel (Sciurus vulgaris) sitting upright in deep snow, Austria, Europe

Edwin Giesbers / Red squirrel (Sciurus vulgaris) sitting upright in deep snow, Austria, Europe

Eric Baccega / Two Polar bears (Ursus maritimus) standing upright, fighting, Churchill, Manitoba, Canada

Niall Benvie / Young male European lynx (Lynx lynx) in broadleaf woodland, Bohemia, Czech Republic.

TJ Rich / European river otter {Lutra lutra} standing on hind legs for better view of surrounding area, England, UK captive

John Downer Productions / Coquerel's sifaka lemurs pogo across the for (Resolution restriction - image digitised from film, 'Weird Nature' tv series)

Juergen & Christine Sohns / Meerkat (Suricata suricatta) pregnant female and juveniles on alert, Tswalu Game Reserve, South Africa

Juergen & Christine Sohns / Meerkat (Suricata suricatta) pregnant female and juveniles on alert, Tswalu Game Reserve, South Africa

Juergen & Christine Sohns / Meerkat (Suricata suricatta) pair on alert, Tswalu Game Reserve, South Africa

Juergen & Christine Sohns / Meerkat (Suricata suricatta) pair on alert, Tswalu Game Reserve, South Africa

Juergen & Christine Sohns / Meerkat (Suricata suricatta) pair on alert, Tswalu Game Reserve, South Africa

Willi Rolfes/ BIA / Alpine Marmot (Marmota marmota) parent feeding with begging young, Hohe Tauern National Park, Austria

Juergen & Christine Sohns / Meerkat (Suricata suricatta) trio on guard, Oudtshoorn, South Africa

Juergen & Christine Sohns / Meerkat (Suricata suricatta) on guard, Oudtshoorn, South Africa

Yva Momatiuk & John Eastcott / Black-tailed Prairie Dog (Cynomys ludovicianus) on alert, Theodore Roosevelt National Park, North Dakota

Suzi Eszterhas / Giant Panda (Ailuropoda melanoleuca) six-to-eight month old cub, Chengdu, China

Theo Allofs / Meerkat (Suricata suricatta) parents and young basking, Makgadikgadi Pan, Kalahari, Botswana

Ingo Arndt / Grizzly Bear (Ursus arctos horribilis) mother and cub in grass, Lake Clark National Park, Alaska

Jim Brandenburg / Arctic Ground Squirrel (Spermophilus parryii) standing guard, Alaska

Pete Oxford / Black-tailed Prairie Dog (Cynomys ludovicianus) looking for danger, Devil's Tower National Monument, Wyoming

Konrad Wothe / Brown Bear (Ursus arctos) sitting upright, Germany

Michael Quinton / Snowshoe Hare (Lepus americanus) feeding on Pussy Willow (Salix discolor) in winter, Alaska

Shin Yoshino / Grizzly Bear (Ursus arctos horribilis) sitting upright, Denali National Park and Preserve, Alaska

Jim Brandenburg / Black-tailed Prairie Dog (Cynomys ludovicianus) barking while standing atop burrow, South Dakota

Staffan Widstrand / Wild Wonders of China / Large leaf of Giant Elephant's Ear (Alocasia odora), in rainforest, Yangminshan, Taiwan