Territory: common hippos live in groups, sometimes known as schools (except for the pygmy hippo which is usually found singly or in pairs). There are 20 - 100 in each group. In the centre of each group's territory there is a creche occupied by females and youngsters; the adult males each have a separate area, known as a refuge, around the creche. The creche is on a sandbar in midstream or on a raised bank of the river or lake. Special paths lead from the males' refuges to the feeding grounds.
The female hippos are the leaders of the schools. When the young males leave the creche, they have to take up a refuge beyond the ring of adult males' refuges lying around the edge of the creche. Each then has to try and win his way to an inner refuge by fighting - and this entitles him to mate with one of the females.
Fights can be very fierce. The hippo's familiar yawn is actually an aggressive gesture, a challenge to fight. The two contestants rear up out of the water, huge mouths wide open, trying to slash each other with their long tusks. Terrible gashes are inflicted but they quickly heal. The aim of a fight is to break a foreleg of an opponent - this is fatal because the animal can no longer walk on land to feed. There are strict rules concerning the behaviour of the males. Outside the breeding season a female may pay a social call on a male and he may visit her - but he must enter the creche with no sign of aggression. If a female gets up on her feet, the male must lie down - and he may only get up when she lies down again! A male who does not keep to these rules is driven out by attacking females.
Daily Life: a hippo spends most of its day basking on a sandbar, or lazing in the water with just its ears, eyes and nostrils, and perhaps its back and top of the head, exposed. It feeds mostly at night, coming on land to eat mainly grass. During one night an individual may wander up to 20 miles but usually does not venture far from water. The areas of grass, kept short by the hippos, are known as hippo lawns.
If frightened, common hippos rush into the water but pygmy hippos prefer to head for the undergrowth. Pygmy hippos are very shy and hard to find. They are usually found singly or in pairs. They are not usually aggressive unless disturbed.
Read More: Threats to the Hippopotamus