Hippopotamus: Facts, Size, Diet and Why Hippos Are Dangerous

What does a hippo look like?

A hippo has a barrel-shaped body, short thick legs, a huge head and a broad muzzle. The skin is gray to purplish brown above and pinkish on the belly and around the eyes and ears. It is almost hairless, apart from stiff bristles on the muzzle and the tip of the tail, and is about 5–6 cm (2 in) thick over much of the body.

The eyes, ears and nostrils sit high on top of the head, so a hippo can see, hear and breathe while almost completely underwater. When it submerges, its slit-shaped nostrils and small ears close tightly. Each foot has four toes joined by a little webbing.

The mouth is the hippo’s most famous feature. The hinge of the jaw sits far back, letting a hippo open its mouth to well over 90 degrees, one of the widest gapes of any land mammal. The lower canines grow throughout life and can reach about 50 cm (20 in) along the curve, and the lower incisors up to 40 cm (16 in). These teeth are weapons, not tools for eating; grass is gathered with the broad, hard lips.

How big is a hippopotamus?

Hippos are big and heavy for their height. Adults usually stand 1.3–1.65 m (4.3–5.4 ft) at the shoulder and measure roughly 2.9–5 m (9.5–16.5 ft) from nose to tail tip, with most adults about 3.3–3.5 m (11 ft) in head and body length.

Bulls and cows look alike, but bulls are on average heavier, with thicker necks and longer tusks. Females stop growing in their mid-20s, while males seem to keep putting on weight for most of their lives, so the heaviest hippos are old bulls. Read more in How much does a hippo weigh?

Habitat and range

Common hippos live in sub-Saharan Africa, in permanent rivers, lakes, swamps and sometimes estuaries. They need water deep enough to cover their bodies during the day, ideally with gently sloping banks, and good grassland within a few kilometers for night grazing. Strongholds include East and southern Africa, especially Tanzania, Zambia, Mozambique and Uganda.

Hippos once ranged far more widely. During warm periods of the Ice Age they lived in Europe, reaching as far north as Britain and the Rhine valley in Germany, and in more recent times they lived along the whole Egyptian Nile. Hunting and persecution wiped them out of Egypt and North Africa, and today the range is broken into many separate populations.

There is also one population outside Africa. In the 1980s the drug lord Pablo Escobar brought a few hippos to his private estate in Colombia. After his death they were left behind, began to breed, and spread along the Magdalena River. They now number well over 100 animals, and Colombia has declared them an invasive species because they compete with native wildlife, foul rivers and create risks for local people.

What do hippos eat?

Hippos are herbivores that feed almost entirely on short grasses. They leave the water around dusk and graze alone for about five or six hours, usually walking 3–5 km (2–3 mi) from the water and sometimes much farther in the dry season. An adult eats roughly 35–40 kg (75–90 lb) of grass a night, which is modest for its size, because it spends the day resting in cool water and digests its food slowly in a long, multi-chambered stomach.

Instead of biting grass with its teeth, a hippo crops it with its wide, horny lips. Constant grazing produces short “hippo lawns” around rivers and lakes. Hippos have also been seen eating carcasses now and then, but this is rare and probably happens when the animals are stressed or short of nutrients.

Life in the water: behavior and social life

By day hippos rest in the water, packed closely together in groups called pods or bloats. A typical group holds 10–30 animals, but more than 100 may gather in a shrinking pool during a drought. Despite living so close together, adults form few lasting bonds, and when they go out to feed, each grazes on its own.

Hippos cannot really swim. Their bodies are too dense to float easily, so they walk or bounce along the bottom and push off to reach the surface. An adult usually comes up to breathe every 3–5 minutes, and a resting hippo can rise and breathe without waking. See Can hippos swim? for details.

Dominant bulls defend stretches of river or lakeshore, typically 50–100 m (160–330 ft) of riverbank or 250–500 m (820–1,640 ft) of lakeshore. Inside his territory the bull mates with the cows and tolerates younger males as long as they behave submissively. Rivals face off with open-mouthed threat displays, and serious fights with the tusks can cause deep wounds.

Hippos are noisy. Their best-known call is the “wheeze honk”, a loud series of grunts that can carry more than a kilometer. They can also call with the head half in the water, so the sound travels through air and water at once. Hippos spread their dung by flicking their tails as they defecate, which may help them mark paths and communicate.

Red “blood sweat”

Hippos lack true sweat glands, but their skin produces a thick fluid that is clear at first and turns red and then brown within minutes. It contains two pigments, red hipposudoric acid and orange norhipposudoric acid, that absorb sunlight like a sunscreen and slow the growth of some bacteria. Because of its color, the fluid was long mistaken for blood. Learn more in Do hippos sweat blood?

Reproduction, life cycle and lifespan

Hippos breed at any time of year, but in many areas most calves are conceived in the dry season and born in the rainy season, when grass is plentiful. Mating takes place in the water. Pregnancy lasts about eight months, and a cow gives birth to a single calf, usually in shallow water or on land, after leaving the group for one to two weeks.

A newborn calf weighs about 25–55 kg (55–120 lb) and can suckle underwater, closing its ears and nostrils as it feeds. Young calves often rest on their mother’s back in deeper water. Mothers are fiercely protective. Calves are weaned at around one year, females reach maturity at about 5–6 years (sometimes earlier) and males at roughly 7 years. Most cows have a calf only every two years or so.

Wild hippos are thought to live about 40–50 years. Zoo hippos often live longer, and two individuals share the record of about 65 years: Bertha at the Manila Zoo in the Philippines and a male called Lu in Florida.

Predators and threats

Adult hippos have very few natural predators. Lions, spotted hyenas and Nile crocodiles kill calves, and large lion prides occasionally bring down an adult, but such kills are rare. Hippos often chase off or attack crocodiles that come too close, and the two share rivers across Africa. Read more about their neighbors in our Nile crocodile profile.

The main threats come from people. Hippos lose access to water and grazing as rivers are dammed, wetlands are drained and farms spread. They are hunted illegally for meat and for their canine teeth, which are sold as a substitute for elephant ivory. Conflict with farmers whose crops they raid also leads to killings.

Conservation status

The IUCN Red List classifies the common hippo as Vulnerable, with an estimated 115,000–130,000 animals and a stable overall trend in its most recent full assessment. Numbers have held up in well-protected areas, but some national populations have collapsed. In Virunga National Park in the Democratic Republic of the Congo, hippos fell from around 29,000 in the 1970s to fewer than 1,000 by 2005 during years of war, before beginning to recover.

International trade in hippo products is controlled under CITES Appendix II, so exports of teeth and other parts need permits. Its smaller cousin, the pygmy hippopotamus of West Africa, is rarer still and listed as Endangered.

Why are hippos dangerous to people?

Hippos are often described as one of the most dangerous large animals in Africa. Bulls defend their stretch of water, mothers guard their calves, and any hippo may charge if it feels cut off from the water. They can overturn small boats and run surprisingly fast on land over short distances. Popular claims that hippos kill around 500 people a year are widely repeated but not based on a reliable continent-wide count. Find out more in Why are hippos so dangerous?

Myths and facts

Myth: hippos are related to pigs. For a long time hippos were grouped with pigs because of their teeth. DNA and fossil studies now show that hippos are the closest living relatives of whales and dolphins; the two lines split roughly 55 million years ago. Read more in Are hippos related to whales?

Myth: hippo milk is pink. This popular claim is false. Hippo milk is white like that of other mammals; the story probably grew from the red skin secretion.

Fact: hippos are fast on land. Despite their bulk, hippos can trot and run at speeds reported up to about 30 km/h (19 mph) over short distances, although this figure has rarely been measured carefully.

Relationship with people

People have lived alongside hippos for a very long time. Ancient Egyptians feared and admired them; the goddess Taweret, a protector of mothers and childbirth, was shown with a hippo’s head. Today hippos are a major draw on safaris and boat trips, and they have long been popular in zoos, where several have become famous. At the same time, farmers and fishers who share rivers with hippos face real risks to their crops, boats and lives, and protecting both people and hippos is a key challenge for conservation in Africa.