Hippopotamus may spend part of the day dozing on sandbanks; their hairless skin protected from the blazing sun by the glandular secretion of a reddish fluid. When a hippo submerges it closes its slitlike nostrils and disappears: adult hippos can remain under water for five to six minutes at a time. Extremely nimble for their size, hippos move easily on their webbed toes as they walk underwater along clearly defined paths on the river bed.
They are nocturnal grazers, and on land, may travel as far as 30 km in a night in search of food. Adult hippopotamus consume about 40 kg of grass per night. They live in social groups, of variable size and composition, during the day: these social groups break up in the evenings and the animals come ashore to graze singly, or as a female with young (a number of young of different ages could accompany the female, with the youngest keeping the closest to the dam/ river). A small percentage of bulls may be territorial, and these territories vary with the size of the dam or water body.
Relationships between territorial bulls and other bulls are extremely friendly, as long as the other bulls are subordinate. A single young is born, in shallow water, and is capable of going into deep water within a few minutes of being born. Calves may be preyed upon by crocodiles, which do not take adult hippos; young hippos are also vulnerable to predation by lions and hyaenas.
The Hippopotamus is characterised by its huge size, short, barrel-shaped body, smooth, naked skin and short, stout legs. Their heads are broad and heavy, with their eyes and nostrils mounted on top: when the head is partially submerged, in the resting position, their eyes and ears are above the water. Their mouths are wide and very large, the jaws armed with curved, tusk-like canines and incisor teeth: despite their comical shape and benign look their jaws and teeth have been known to snap a man in half. Enraged bulls and cows with calves sometimes storm boats, so it is best to stay well clear of them at all times.
Their name is derived from the Greek for ‘water or river horse’. As they are amphibious (they require both land and water), they are confined to adequate aquatic habitats, and so have a patchy distribution, although they are great wanderers, and have been known to cross fairly large expanses of land. They spend much of the daytime in water, where mating and calving take place. Hippos spread their dung out by rotating their tails.