Male lion cub and male Puli dog

Zimba, a male lion cub and Bogi, a male Puli dog, are seen at Gyoengyoes zoo in Hungary. Zimba was donated to the zoo by a private donor in Italy, and will be raised by Bogi.

Polar bear cub

Polar bear cub Wilbaer swims with his mother Corinna in their enclosure at the Wilhelma zoo in Stuttgart during his first appearance April 16.

A panda cub

A panda cub walks at the Chengdu Research Base of Giant Panda Breeding in Chengdu, Sichuan province. The giant panda is one of the world's most endangered species and is found only in China. An estimated 1,600 wild pandas live in nature reserves in Sichuan, Gansu and Shaanxi provinces, and 217 are kept in captivity.

Rocky the grizzly bear

Rocky the grizzly bear is seen at the Forever Wild animal sanctuary in Phelan, California.

Canada's polar bears

A polar bear cub eats a fish as he just woke up after winter sleeping at a zoo. Some of Canada's polar bear populations risk being wiped out within four decades because of climate change and human activity including hunting, the World Wide Fund For Nature warned.

Austria's brown bears

A brown bear shakes the water from his fur while exiting a stream. Austria's brown bear population is facing extinction as only two of the animals -- both males -- are still alive out of a population that had numbered at least 35, the World Wildlife Fund said.