There are two kinds of hippos.
Hippos live on land and in the water.
They can stay under the water for a long time.
A baby hippo is a calf.
Hippos are fierce.
The word 'hippopotamus' means 'river horse' because they walk or run along the bottom of the river, even though they are good swimmers.
There are two species, or kinds, of hippopotamus: the common or river hippopotamus and the pygmy hippopotamus. Both are herbivores.
A young hippopotamus is called a calf. Its father is a bull and its mother is a cow.
Common hippos live in groups, and a group is called a bloat of hippos. Pygmy hippos are solitary, which means they live alone. Sometimes they are in pairs.
The habitat of the common hippopotamus is grassland areas where there is permanent still water, not too deep and without many rocks at the bottom of the pool.
The habitat of the pygmy hippopotamus is in forests in western Africa, near swampy areas.
The pygmy hippopotamus is much smaller than the common hippo, standing at less than 1 metre high at the shoulder and weighing about 250kg. Its neck is longer, its head is rounder and narrower, and its eyes are not at the top of its head. They spend less time in the water than the common hippopotamus, but have the same adaptations to being in water.
The common hippopotamus weighs about 3 tonnes (male) and 1.5 tonnes (female). It is the third largest land animal (after the elephant and rhinoceros). Its feet have four webbed toes. Hippos have very thick skin and almost no hair. The hippopotamus does not sweat, so they need water or mud in order to keep cool. When out of water for a while, its skin sometimes oozes a pinkish, oily liquid. Some people think this is blood but it is not. This liquid prevents the skin from drying out and acts as a sunscreen. Under the skin a hippo has a thick layer of fat, which helps keep it warm in the water.
Eyes, ears and nostrils are on the top part of the head so that when floating in the water they can see, hear and breathe easily. Hippos have short, flattened tails. The tail acts like a bat to spread the animal's poo to mark its territory.
Underwater, hippos run or walk along the bottom, with their ears pressed down flat and their nostrils clamped shut by tiny muscles. Their heart rate slows down so they can stay underwater longer. They generally come up for air every 6 or 7 minutes, but they can stay under for about 30 minutes.
Hippopotamus live both on land and in the water, which means they are amphibious. The common hippopotamus comes out of water at night to feed on grass, often walking up steep banks and always following the same paths. They generally return to the water at sunrise to spend the morning dozing. They may lie on the banks to sunbake if it is not too hot or windy. On land they can run at about 30 kilometres an hour if they have to, but only for a short distance.
Common hippopotamus groups vary in size. In a large pool, a group could be as large as 60. Males are very territorial. Hippopotamus are very aggressive animals and easily enraged. They 'yawn' more and more as they get angrier, showing their big teeth as part of their threat display.
Pygmy hippos live alone or in pairs. They also feed at night. They eat grass, leaves and fruit. Not a great deal is known about these rare animals.
A female common hippopotamus gives birth to a single calf, very rarely twins, about 8 months after mating with a male. Hippopotamus calves are small, about 25kg, born on land or in shallow water. Hippos are mammals, so the young drink milk, and hippo calves generally suckle milk from their mothers while underwater. The calves of the herd play together. In the water, young ones are often seen resting their heads, or standing, on an adult's back, usually their mother's, because the effort to keep afloat tires them too much. Until a calf is strong enough to walk far, the mother leaves it with other females to babysit when she goes to feed.