Common hippopotamus

Hippos eat grass.

They come out of the water when it gets dark. They walk to the grass and eat for many hours. They go back to the water in the morning.

Hippos are grazers. After sunset they leave the water and follow the same paths, sometimes as far as 10 kilometers, to grassy areas. They spend five or six hours eating, pulling up grass with their wide, tough lips rather than biting it with their teeth.

A hippo eats about 35 to 40 kilograms of grass a night. That sounds like a lot, but it is a small meal for such a big animal. Floating in warm water all day saves a lot of energy.

Hippos graze at night on short grass near water, gripping it with broad, muscular lips and jerking the head; the long canines and incisors play no part in feeding. They eat about 35 to 40 kilograms a night, only around 1 to 1.5 percent of body weight, because resting in warm water keeps their energy needs low.

Hippos do not chew the cud, but food stays a long time in the stomach, where it ferments and protein is extracted. Feeding on land and resting in water makes hippos a nutrient pump: they carry large amounts of plant matter, as dung, from grasslands into rivers and lakes. That input feeds fish, which in turn are an important food for many people living nearby.

Hippos live in groups.

They rest together in the water. They are very noisy! They grunt and honk to talk to each other. A big yawn means 'give me space'.

Hippos live in groups of about 10 to 30, resting close together in the water. A big male guards a stretch of river. He shows other males it is his by spraying dung with his flicking tail.

Hippos are noisy. They grunt, snort and make loud 'wheeze-honks', and some calls carry both through the air and under the water. A wide yawn is not sleepiness: it is a warning that says 'stay back'. Hippos need lots of space, so people always watch them from a safe distance.

Groups of about 10 to 30 animals, occasionally many more, share pools. A dominant bull holds a stretch of river as a mating territory, sometimes for 12 years or more, tolerating subordinate males that do not try to breed. Neighboring bulls advertise their territories by spraying dung with a rapidly wagging tail, and dung piles along land paths probably act as scent signposts at night.

Hippos are vocal on land and in water; San Diego Zoo describes them as the only mammals known to make amphibious calls, with some measured at 115 decibels. Gaping, splashing and bluff charges are threat displays. Hippos are territorial and can be dangerous to people who come too close, especially in boats, so in the wild they are watched only from a distance.

Hippos need clean rivers and lakes.

People are protecting the places where hippos live. Parks help keep hippos safe.

Hippos are listed as Vulnerable. Farms and towns are spreading onto the grasslands they graze, and dams and canals change the rivers they need. Some hippos are hunted illegally for their meat and for their large teeth, which are carved like ivory.

National parks give hippos the best protection. Keeping rivers flowing and helping farmers protect their crops lets people and hippos share the land more safely.

The IUCN lists the common hippo as Vulnerable (2016 assessment), with a stable overall trend but declines in many places. A 2008 assessment, cited by Britannica, estimated 126,000 to 149,000 animals. The main threats are loss of riverside grazing, dams and water diversion for farming, conflict over crops, and illegal hunting for meat and canine teeth. Demand for hippo 'ivory' rose after the 1989 ban on the international elephant ivory trade.

Because hippos depend on a narrow strip of water and nearby grass, they are vulnerable when rivers are altered. Losing them would also affect river ecosystems that rely on the nutrients they bring from land. Protected areas, controls on the teeth trade and work with farming communities are the main conservation tools.