Hippopota­muses: Mighty herbi­vores

What you need to know about hippos

When thinking about the most dangerous animal in Africa, the hippo is probably not the first animal that comes to your mind. But this fascinating and impressive animal is the number one reason for incidents between humans and animals – despite the fact that hippos are vegetarians.

The hippo is one of the biggest herbivorous mammals living in Africa. It is assigned to the family of Hippopotamoids and is related to our domesticated pigs. They are even-toed ungulates and the first description of a hippo originates from the Nile River.

Hippos and their physical characteristics

Adult animals can reach a height of 1,50 meters and a body length of 4,50 meters – of which 50 cm are the short and flattened tail. They weight between 2700 and 4500 kg, their big and relatively flat head alone weighs about 450 kg. All together the hippo is the second largest land-living mammal after the elephant.

Hippos can run up to 48 km per hour. During the day they can be found in the water. Sometimes only their ears, eyes and nostrils are visible while the rest of their head/body is underwater.

The ears are very small in comparison to the rest of their body. Hippos are equipped with 44 teeth: Both jaws show three incisors, one canine tooth, four premolars and three molars. The lower incisors are in an upright position and form gigantic tusks. They work against the upper canine teeth which sharpens them and turns the canine teeth and incisors into a dangerous weapon.

Short pillar-like legs carry a clumsy-looking, barrel-shaped body which is almost naked. The skin has a grey-brownish colour but changes to a yellow-pinkish shade in the area of the ears and eyes.

Hippos and their habitat

In the past, the hippo occupied the whole African continent. Today it can only be found in Sub-Sahara Africa and became extinct in the lower Nile region and Capeland as well as in most parts of western Africa.

Hippos prefer rivers with a slow velocity and a water temperature between 18 and 35°C. They are also often found in rivers with sandy beaches or river banks. The water must be deep enough to cover the whole body of the hippo. For feeding the hippo needs grassland which is close to the river to graze.

Hippos are perfectly adapted to life in water: On land they loss so much water by sweating and get sunburned really fast. Their skin is equipped with a pinkish colored slime, excreted by cutaneous glands, especially when the hippos are aroused.

The are also able to close their nostrils, which enables the hippo to dive under water for round 10 minutes. Hippos spent almost their whole life in the water but are not good swimmers. They either run on the ground of the waterbody or float around.

Hippos and their social behaviour

Usually hippos live in groups of up to 20 animals, so-called “hippo schools”. These groups are led by females and have territories in water and on land. The bulls mark their territory by rotating their tail and spreading excrements on grass, bushes and in the water.

Older bulls are sometimes seen living solitary, but usually they also live in groups with females and their youngsters. Younger bulls are chased away by older bulls when they become sexually mature.

Hippos are very territorial and start aggressive fights with other bulls which can end deadly. When they open their mouth, it seems as if the hippo is yawning but in fact this is threatening gesture.

Hippos and their diet

At night they leave the water and graze on nearby fields. Hippos need up to 50 kg of food every day. Areas which are situated next to a river with a slow current and appear like perfectly mowed lawn are usually an indicator for hippos being in the area.

To reach their grazing field hippos sometimes also walk for long distances, like five to ten kilometres. In that case they form so-called Hippo trails which are used by the entire hippo school.

Hippos and their reproductive behaviour

Hippos give birth after a 340-day pregnancy. Often many cows calve at the same day. Male hippos usually stay with their mothers for about two years before they have to leave the hippo school. In general, females stay with the herd for their whole life. Between the age of four and five the reach pubescence. Their life expectancy in the wild is around 35 years, while in zoos they can become even older.

Hippos mate under water during the beginning of the dry season and give birth also under water to a single calf after 8 months in the rain season. While mating the cow is constantly under water and only gets up to the surface for fresh air.

The newborn calf weighs between 30 and 50 kg and can walk and move underwater straight after birth. This is important because the mothers nurse their newborns under water and they must be able to follow their mother on land when she goes out grazing during the night.

To create a strong bond between her and the calf, the mother does not let any other hippo get close to her calf during the first days. Then, after a couple of days, they both join the rest of the group. The calf feeds only on its mothers’ milk during the first week, before it slowly starts to add plants to the daily meals. The young one stays close to its mother for around seven years.

After six years the females become sexually mature. Depending on the stand density there can be great differences, which can lead to a natural regulation of the population. Cows give birth approximately every 2 years.

The bulls reach sexual maturity when they are between six and eight years old but often do not have their own territory by then. Therefore, the bulls often start mating when they are already 20 years old or even later.

Hippos as an endangered species

Because of their flavourful meat, their durable skin which is used to make the famous Sjambok and the ivory of their teeth or just for pleasure, hippos have been hunted by humans for decades. A population of 125000 to 148000 is the estimation of the IUCN. Due to the decreasing population the Hippopotamus is listed as endangered.

Sources

Natur-Lexikon
Transafrika
Ronald M. Nowak: Walker’s Mammals of the World. Johns Hopkins University Press, Baltimore 1999