When you think of rivers in the savanna areas of Africa, you probably think of the tank-like hippo whose name means river-horse.

They are not related to any land animal, but to ocean mammals like whales and dolphins.

Staying in the water helps to keep them cool during the day.

Hippopotamuses are actually grazing animals. They eat almost exclusively grass. . They slosh about in the water during the day, and gape with huge jaws, making them seem terrifying when close, but they are not hunters, and don't usually eat meat at all.

Hippos are the third largest land animal, can weight one and a half tonnes, and despite their shape, they can run at 20 miles an hour.

Hippos like to be left alone. If anything comes too close they become aggressive, and their speed makes them one of the most dangerous animals in the world if they decide to attack. But that is of no concern to oxpecker and other birds, who happily sit on a hippos back and eat the ticks attached to its skin.