The Book of Job describes a monster, a behemoth, which is probably a hippopotamus. These beasts are huge, with adults weighing over 1.5 tonnes. The males don’t stop growing until they die, but the weights of females start levelling off at age 25 years. I was astonished when I looked down on a hippo from the Luangwa River Bridge and saw how broad in the beam it was. Hippos are barrel-shaped. Only elephants and rhinos are more massive land animals. 55 million years ago, they diverged from their nearest relatives, the whales.
On land, they can run fast for short periods, up to 20 mph. Normally, they trot briskly when getting away from a threat. When there is no danger, they walk slowly, often using the same route, leaving a set of parallel ruts, too narrow for a vehicle to use.
They have thick skins (5 centimetres) but surprisingly not much subcutaneous fat. If they stay out of the water for too long during the day, their skin gets damaged and cracks. Hippos secrete a substance which turns pink in sunlight and protects them from UV radiation. It also has an antibiotic action.
They spend most of their time in pools or shallow rivers. They can’t float and cannot swim well, even though they have webbed toes. In deep water they move by bouncing off the riverbed. They avoid fast flowing rivers or keep to the edge where the current is less strong.
Oxpeckers remove parasites from the hippo skin, but they can irritate by keeping a wound open so they have access to nutritious blood.
All the important bits of a hippo are situated on the top of its head: eyes, ears and nostrils. It can shut its nostrils when it submerges, and can stay underwater for over five minutes before surfacing to breathe. Baby hippos are born underwater and have to learn to swim immediately.
Hippos usually live in large groups, called pods, with up to a hundred members. They are territorial, occupying 100-200 metres stretches of river. A big male tolerates younger males if they are submissive and stay away from the females. If they challenge and get defeated, they may be forced to leave the pod and become solitary.
Sex occurs in the water, with the female being submerged for most of the time while the male mounts her. Pregnancy lasts eight months and the young hippo suckles from its mother until it is weaned at about a year.
Hippos have a reputation for being aggressive if a boat transgresses on their territory or if they feel threatened on land (don’t get between them and the water or between a mother and her calf). They probably kill more people than crocodiles and elephants. They forage at night on land, eating mainly grass and vegetation.
People do like to eat hippo flesh, which apparently tastes like muddy, fishy pork. I have never knowingly eaten it.