Berlin Zoo's baby hippopotamus

Berlin, Germany: December 16 2008: A baby hippopotamus swims with her mother on her first day in the public eye at Berlin Zoo. She was born on November 29 Photograph: Michael Kappeler/Getty Images

The calf was kept away from the other hippos in the zoo for the first two weeks of her life, while she bonded with her mother. In the wild hippos are gregarious, and live in groups of up to 40 Photograph: Michael Kappeler/AFP/Getty Images

Female hippos reach sexual maturity at five to six years old and have a gestation period of eight months. Baby hippos are born underwater and must swim to the surface to take their first breath. Calfs rest on their mother's back when in deep water and swim underwater to suckle Photograph: Michael Kappeler/AFP/Getty Images

Hippos have been popular zoo animals since the first captive hippo, called Obaysch, arrived at London Zoo in 1850. Obaysch attracted 10,000 visitors a day and inspired a popular song, the Hippopotamus Polka. The calf is not the first animal to catch the public's attention at Berlin Zoo - in 2006 Knut the polar bear won worldwide attention when the zoo decided to hand rear the cub Photograph: Michael Kappeler/AFP/Getty Images

Hippos were widespread in north Africa and Europe before the last ice age, and can live in colder climates provided the water does not freeze. They were declared a vulnerable species in 2006 when the population was estimated to be between 125,000 to 150,000, a decline of 7% in 10 years. Adult hippos grow to weigh two tonnes Photograph: Sean Gallup/Getty Images