Hippopotamuses graze on grass during the night and rest in or near the water during the day. In fact, the hippo┐s day revolves around the water. If danger threatens whilst it is grazing it will head back into the water. Adult bulls are extremely territorial and a strong male hippo will control his territory in and out of the water. Hippopotamuses mark their territory with their dung, spraying the faeces over a shrub or rock. In water it is spread with their tail, which is flattened for the purpose. The dung also acts as food for micro-organisms, which form part of the natural food chain in rivers.

Territorial fights amongst hippos are vicious and very often fatal. Fights can go on for hours, with each contender trying to inflict deep gash wounds on its opponent with its razor sharp incisor teeth. Few adult hippo bulls are without the scars from such battles. Lone bulls find refuge in their own pools from where they launch an attack on the herd bull and attempt to take over the harem. Hippos are extremely aggressive and unpredictable animals and will often charge other animals, passing boats and even humans.

The hippo is well adapted to water, with a pinkish oily secretion helping protect its skin. It can remain completely submerged in water for up to 30 minutes, but its normal dive lasts only around 5 minutes. Usually though, it just soaks in the water with only its eyes and slit-like noses above it. Even though it is a large animal, the hippo moves easily through the water, walking on the bottom of rivers with the grace of a swan.

Hippos are gregarious animals, living in small herds of 20 to 40 individuals. These herds consist of one adult bull, a number of cows and their young. Young bulls are evicted from the herd on reaching sexual maturity. The herd travels together and may wander up to 20 miles at night. Their main predators are man and crocodiles, which attack the young.

Diet

Hippopotamuses are grazers feeding on short grass, reeds and other vegetation, including fallen fruits. They feed at night leaving the water to search for feeding grounds, typically following the same route each time, grazing under the moonlight. An adult hippo will consume as much as 68 kilograms of grass a day. They possess a three-chambered non-ruminating stomach.

Adaptations

The eyes and nostrils are raised on small projections on the head so that they remain above the water when the rest of the head is submerged. This allows the hippo to retain sight and hearing while partially submerged. Beneath the skin is a special protective layer of fat, and an oily substance on the skin keeps the hippo moist in the sun.