Young Galapagos sea lion bulls (Zalophus wollebaeki) mock-fighting in the Galapagos Islands, UNESCO World Heritage Site, Ecuador, South America

Young Galapagos sea lions (Zalophus wollebaeki) at play underwater in the Galapagos Island Archipelago, UNESCO World Heritage Site, Ecuador, South America

Chacma Baboons (Papio ursinus), two youngsters playing tug of war with one youngster's tail, Chobe National Park, Botswana

Male southern elephant seal (Mirounga leonina) pups mock fighting on South Georgia Island, Southern Ocean

Male southern elephant seal (Mirounga leonina) pups mock fighting on South Georgia Island, Southern Ocean

Male southern elephant seal (Mirounga leonina) pups mock fighting on South Georgia Island, Southern Ocean

An adult Pacific white-sided dolphin (Lagenorhynchus obliquidens) bow-riding in Johnstone Strait, British Columbia, Canada

Young brown bear (Ursus arctos) scratching its back on the gravel at the Brooks River, Katmai National Park, Alaska, United States of America

A pod of Pacific white-sided dolphins (Lagenorhynchus obliquidens) leaping and surfacing in Johnstone Strait, British Columbia, Canada, North America