George Sanker / White-tailed deer (Odocoileus virginianus) doe and fawn at edge of beaver pond. Acadia National Park, Maine, USA. June.

George Sanker / White-tailed deer (Odocoileus virginianus) doe with suckling fawn at edge of beaver pond. Acadia National Park, Maine, USA. June.

George Sanker / Grizzly bear (Ursus arctos horribilis) female and older cub, amongst flowers in meadow. Grand Teton National Park, Wyoming, USA. June.

George Sanker / Elk (Cervus canadensis), two cows and calf silhouetted on ridge at dusk. Yellowstone National Park, Wyoming, USA. June.

George Sanker / Grizzly bear (Ursus arctos horribilis) female with sub-adult cub rolling on back, in grassland. Yellowstone National Park, Wyoming, USA. June.

George Sanker / Grizzly bear (Ursus arctos horribilis) female and sub-adult cub play fighting. Yellowstone National Park, Wyoming, USA. June.

George Sanker / Grizzly bear (Ursus arctos horribilis) female and sub-adult cub walking along river bank at woodland edge. Yellowstone National Park, Wyoming, USA. May 2018.

George Sanker / Black bear (Ursus americanus) female and cubs on rocky slope. Yellowstone National Park, Wyoming, USA. May.

Alex Mustard / Box crab (Calappa sp.) female emerging from the sand and shakes her body to release her tiny young. Dauin, Dauin Marine Protected Area, Dumaguete, Negros, Philippines. Bohol Sea, tropical west Pacific...

Sergio Hanquet / Short-finned pilot whale (Globicephala macrorhynchus) female carrying dead calf below water surface. Tenerife, Canary Islands.

Sergio Hanquet / Short-finned pilot whale (Globicephala macrorhynchus) female and calf. Tenerife, Canary Islands.

Sergio Hanquet / Short-finned pilot whale (Globicephala macrorhynchus), four including female and calf, swimming below surface. Tenerife, Canary Islands.

Nick Garbutt / Puma (Puma concolor puma) female with sub-adult cubs aged 12 to 13 months, walking amongst thrombolites and stromatolites on shore of Laguna Sarmiento. Estancia Amarga, near Torres del Paine National...

Nick Garbutt / Puma (Puma concolor puma) female with sub-adult cubs aged 12 to 13 months, resting amongst thrombolites and stromatolites on shore of Laguna Sarmiento. Estancia Amarga, near Torres del Paine National...

Nick Garbutt / Puma (Puma concolor puma) female and three sub-adult cubs aged 12 to 13 months attempting to dig out Armadillo from burrow. Estancia Amarga, near Torres del Paine National Park, Patagonia, Chile. Dece...

Nick Garbutt / American bison (Bison bison) female with calf, running through snow. Hayden Valley. Yellowstone National Park, USA. February.

Nick Garbutt / Puma (Puma concolor puma) female with sub-adult cubs aged 12 to 13 months, lying amongst thrombolites and stromatolites on shore of Laguna Sarmiento, near Torres del Paine National Park, Patagonia, Ch...

Nick Garbutt / Puma (Puma concolor puma) female and two sub-adult cubs aged 12 to 13 months. Estancia Amarga, near Torres del Paine National Park, Patagonia, Chile. December.

Nick Garbutt / Coscoroba swan (Cisne coscoroba) female and chicks, swimming in a row. Torres del Paine National Park, Patagonia, Chile. November.

Yashpal Rathore / Female cheetah (Acinonyx jubatus) named Silgi (means 'bright future' in Swahili) walking with 7 cubs. Masai Mara National Reserve, Kenya

Yashpal Rathore / Female cheetah (Acinonyx jubatus) named Silgi (means 'bright future' in Swahili) with seven cubs, carrying prey. Masai Mara National Reserve, Kenya.

Yashpal Rathore / Cheetah (Acinonyx jubatus) female named Silgi (means 'bright future' in Swahili) walking with 7 cubs. Masai Mara National Reserve, Kenya

Yashpal Rathore / Female cheetah (Acinonyx jubatus) named Silgi (means 'bright future' in Swahili) walking with 7 cubs. Masai Mara National Reserve, Kenya

Ben Cranke / Lion (Panthera leo) female and cubs, one cubs a leucistic white male. Greater Kruger National Park, South Africa.

Ann & Steve Toon / White rhino (Ceratotherium simum) female and calf looking in opposite directions, reflected in waterhole at night. Zimanga private game reserve, KwaZulu-Natal, South Africa.

Dong Lei / Tibetan partridge (Perdix hodgsoniae) female and chick. Sanjiangyuan National Nature Reserve, Qinghai Province, Qinghai-Tibet Plateau. August.

Doc White / Risso's dolphin (Grampus griseus) female and calf aged two days, swimming at surface. California, USA.

Doc White / Risso's dolphin (Grampus griseus) female and calf aged two days, swimming at surface. Calf with head out of water, many scars on female. California, USA.

Doc White / Risso's dolphin (Grampus griseus) female and calf aged two days, swimming at surface, exhaling. California, USA.

Doc White / Risso's dolphin (Grampus griseus) female and calf aged two days, swimming at surface. California, USA.

Gabriel Rojo / Southern right whale (Eubalaena australis) female and calf swimming at water surface. Valdes Peninsula, Patagonia, Argentina. October.

Karine Aigner / Scaled quail (Callipepla squamata) female and chick perched on branch. Texas, USA. June.

Melvin Grey / Turtle dove (Streptopelia turtur) female feeding chicks on nest. Ranmore Common, near Dorking Surrey, England, UK. July.

Melvin Grey / Cheetah (Acinonyx jubatus) female and cubs. Ndutu, Tanzania.

Tony Heald / Arabian horse, female and foal trotting one behind the other. Namibia.

Sven Zacek / Ural owl (Strix uralensis) female watching fledgling learning to climb and balance on branch. Owlet's first day out of nest. Tartumaa County, Southern Estonia. June.

Sven Zacek / Ural owl (Strix uralensis) female watching fledgling attempting to balance on branch. Owlet's first day out of nest. Tartumaa County, Southern Estonia. June.

Kristel Richard / Brown-throated three-toed sloth (Bradypus variegatus) female and baby climbing tree in tropical rainforest. Corcovado National Park, Osa Peninsula, Costa Rica.

Yashpal Rathore / Sloth bear (Melursus ursinus) female carrying cub on back. Nilgiri Biosphere Reserve, India. Camera trap image.

Yashpal Rathore / Sloth bear (Melursus ursinus) female and cubs, carrying cub on back. Nilgiri Biosphere Reserve, India. Camera trap image.

Steven David Miller / Little red flying fox (Pteropus scapulatus) female and baby, hanging with feet down to defecate. Nitmiluk National Park, Northern Territory, Australia.

Steven David Miller / Little red flying fox (Pteropus scapulatus) female and suckling baby in flight, searching for place to roost. Nitmiluk National Park, Northern Territory, Australia.

Loic Poidevin / Brown bear (Ursus arctos) female and two cubs. In coniferous forest, Finland. May.

Felis Images / Bengal tiger (Panthera tigris) female and two cubs walking through grass, female carrying cub in mouth. Bandhavgarh National Park, Madhya Pradesh, India. Photo Phillip Ross/Felis Images

Felis Images / Rusty spotted cat (Prionailurus rubiginosus) female and kittens in woodland. Tadoba Andhari Tiger Reserve, Maharashtra, India. Photo Harsha Narasimhamurthy/Felis Images

Felis Images / Asiatic lion (Panthera leo persica), two females and two cubs. Gir National Park, Gujarat, India. Photo Phillip Ross/Felis Images

Sandesh Kadur / Bengal tiger (Panthera tigris) female and cubs swimming in pond. Ranthambore National Park, India.

Sandesh Kadur / Bengal tiger (Panthera tigris) female and cubs cooling down in waterhole. Ranthambore National Park, India.

Tony Wu / Humpback whale (Megaptera novaeangliae australis) female with calf swimming above head. Rake marks on fluke created by Orca or False Killer whale predators. Vava'u Islands, Tonga.

Tony Wu / Skeleton shrimp (Caprella bispinosa) female and babies on Sea lettuce. Venomous spikes on female used to protect young. Hokkaido, Japan. May.

Juan Carlos Munoz / Sorraia horses, adult and two foals standing in meadow. Middle Coa, Coa Valley, Western Iberia, Portugal. April 2016.

Juan Carlos Munoz / Sorraia horses, mare and foal standing amongst wildflowers in meadow. Middle Coa, Coa Valley, Western Iberia, Portugal. April.

Yashpal Rathore / Asian elephant (Elephas maximus) female feeding grass with her calf, Jim Corbett National Park, India

Yashpal Rathore / Indian leopard (Panthera pardus fusca) female resting, with male and cubs interacting near its rocky cave in hillock situated close to human settlement, Rajasthan, India

Yashpal Rathore / Bengal tiger (Panthera tigris) female with her cubs sharing small water pool, Tadoba National Park, India

Ingo Arndt / Puma (Puma concolor) female with young cub, on slope amongst scrub. Torres del Paine, Patagonia, Chile. July.

Ingo Arndt / Puma (Puma concolor) female and two playing cubs. Torres del Paine, Patagonia, Chile. January.

Ingo Arndt / Puma (Puma concolor) female and cubs on rock. Torres del Paine, Patagonia, Chile. December.

Bernard Castelein / Nursery web spider (Pisaura mirabilis) female guarding spiderlings, Peerdsbos, Brasschaat, Belgium. July

Bernard Castelein / Nursery web spider (Pisaura mirabilis) female guarding spiderlings, Peerdsbos, Brasschaat, Belgium. July

Eric Baccega / Giant panda (Ailuropoda melanoleuca) female and juvenile cub aged 2 years, feeding on Bamboo. Yuan Meng was the first Giant panda to be born in France. Zoo Parc de Beauval, France. Captive.

Ingo Arndt / Puma (Puma concolor) female and two cubs snuggling on hillside. Torres del Paine, Patagonia, Chile. July 2017.

Ingo Arndt / Puma (Puma concolor) female and cubs feeding on Guanaco (Lama guanicoe) carcass. Torres del Paine, Patagonia, Chile. July.

Jack Dykinga / Burrowing owl (Athene cunicularia) chick pestering female by tugging at tail feathers. Marana Arizona, USA. May.

Jack Dykinga / Burrowing owl (Athene cunicularia) female feeding chicks after receiving food from male on right. Marana, Arizona, USA. May. Sequence 2/2.

Jack Dykinga / Burrowing owl (Athene cunicularia) fledgling begging female for food. Marana, Arizona, USA. May.

Jack Dykinga / Burrowing owl (Athene cunicularia) female and three chicks. Marana, Arizona, USA. May.

Jack Dykinga / Burrowing owl (Athene cunicularia) female feeding Colorado river toad (Incilius alvarius) to chick. In evening light, Marana, Arizona, USA. May.

Andy Rouse / Gray langur (Semnopithecus sp) female and baby, backlit in evening light. Ranthambhore National Park, India.

Andy Rouse / Bengal tiger (Panthera tigris) female walking followed by two cubs. Along lake shore, Ranthambhore National Park, India.

Andy Rouse / Bengal tiger (Panthera tigris) female and cubs. Ranthambhore National Park, India.

Andy Rouse / Bengal tiger (Panthera tigris) female and cubs. Ranthambhore National Park, India

Andy Rouse / Bengal tiger (Panthera tigris) female and cub walking, portrait. Ranthambhore National Park, India.

Andy Rouse / Bengal tiger (Panthera tigris) female and cub, portrait. Ranthambhore National Park, India.

Andy Rouse / Bengal tiger (Panthera tigris) female and cubs walking through forest. Ranthambhore National Park, India.

Andy Rouse / European red fox (Vulpes vulpes) female with three cubs. UK. November.

Steven David Miller / Eastern grey kangaroo (Macropus giganteus) female with joey in pouch. Grampians National Park, Victoria, December.

Steven David Miller / Agile wallaby (Macropus agilis) female and joey foraging in campground. Nitmiluk National Park, Northern Territory, Australia.

Steven David Miller / Agile wallaby (Macropus agilis) female and joey standing side by side. Pouch visible on female. Nitmiluk National Park, Northern Territory, Australia.

Steven David Miller / Agile wallaby (Macropus agilis) female cleaning herself with joey squeezed into pouch. Nitmiluk National Park, Northern Territory, Australia.

Steven David Miller / Agile wallaby (Macropus agilis) female with joey in pouch, foraging in campground. Nitmiluk National Park, Northern Territory, Australia.

Steven David Miller / Agile wallaby (Macropus agilis) female with joey in pouch, joey's limbs no longer fit in pouch. Nitmiluk National Park, Northern Territory, Australia.

Steven David Miller / Eastern grey kangaroo (Macropus giganteus) female with joey in pouch, standing beside tree. Grampians National Park, Victoria, Australia.

Robin Chittenden / Common otter (Lutra lutra) female and kit resting on old jetty. East Anglia, England, UK. April.

Gabriel Rojo / Orca (Orcinus orca) female and calf in coastal waters. Punta Norte, Valdez Peninsula, Argentina. May.

Matthew Maran / Juvenile Red fox (Vulpes vulpes) stalking its mother, playing, London, England, UK, June.

Matthew Maran / Red fox (Vulpes vulpes) vixen grooming her cub in an allotment, London, England, UK, July.

Matthew Maran / Red fox (Vulpes vulpes) vixen grooming her cub at dusk, London, England, UK, June.

Matthew Maran / Red fox (Vulpes vulpes) vixen grooming her cub in an allotment, with cars passing behind, London, England, UK, June.

Matthew Maran / Red fox (Vulpes vulpes) vixen watching her cubs playing in an allotment, chasing each other, London, England, UK, June.

John Chan / Female Downy woodpecker (Picoides pubescens) feeding nestling, Southern California, USA, May.

John Chan / Pair of Downy woodpeckers (Picoides pubescens) feeding their chick, Southern California, USA, May.

John Chan / Female Downy woodpecker nestling (Picoides pubescens) peering out and calling from the entrance of its nest cavity, begging to be fed, Southern California, USA, May.

Doug Gimesy / Grey-headed flying foxes (Pteropus poliocephalus) female carrying her pup whilst in flight, Yarra Bend Park, Kew, Victoria, Australia. December.

John Cancalosi / House sparrow (Passer domesticus) female feeding chicks at nest in Saguaro (Carnegiea gigantea) cactus. Non-native bird species that competes with native species for nesting cavities in cacti. Sonoran...