Tony Wu / Humpback whale (Megaptera novaeangliae australis) female with suckling calf. Vava'u Islands, Tonga.

Mark Raycroft / Woodland Caribou (Rangifer tarandus caribou) mother nursing calf, Newfoundland, Canada

Suzi Eszterhas / Leopard (Panthera pardus) six-week-old cub nursing, Jao Reserve, Botswana

Eric Baccega / Female Uganda kob (Kobus kob thomasi) suckling calf. Murchisson Falls National Park, Uganda. February.

Luke Massey / Wild boar (Sus scrofa) piglets suckling from mother, Forest of Dean, Gloucestershire, England, UK, May.

Philippe Clement / European brown bear (Ursus arctos arctos) cubs suckling from mother in the snow in winter, Bavarian Forest National Park, Germany, January. Captive.

Dave Bevan / Juvenile Herring gull (Larus argentatus) pecking a suckling Grey seal (Halichoerus grypus) pup, Norfolk, England, UK. December.

Brian Bevan / Grey seal (Halichoerus grypus) pup trying to suckle, Norfolk, England, UK, January.

Ingo Arndt / Eastern grey kangaroo with joey suckling (Macropus giganteus) Australia

Ingo Arndt / Dromedary camel suckling {Camelus dromedarius} Rajasthan, India

Sam Hobson / Red fox vixen (Vulpes vulpes) with young cubs. Bristol, UK. April

Cyril Ruoso / Golden monkey (Rhinopithecus roxellana) female with young suckling, Qinling Mountains, China.