Species: Hippopotamus amphibius
Basic hippopotamus facts:
Hippos are the third largest land mammal species on Earth, after elephants and white rhinos. Weighing in at around 7,900 pounds (3,600 kilograms), adult hippos measure about 15 feet (4.6 meters) long and 5 feet (1.5 m) tall. [Video: Hippo Weighed on Giant Scale]
Their skin color varies from brown to grayish purple, and they're almost completely hairless. To protect their bare skin, hippos produce a special kind of sweat that's red and acts as sunscreen, insect repellent and antibiotic salve, all in one.
This hulk of an animal wallows by day and grazes by night. During the day, they rest, play and sometimes fight in lakes, rivers and swamps. They get down to business at night, grazing on land for hours at a time. They're usually sluggish out of the water — though they can run at speeds up to 30 mph (48 kph) — but underwater, they gracefully gallop and walk along river and lake bottoms.
Hippos are well adapted to their amphibious lifestyle. They have wide snouts and thick lips that help them graze on tough African grasses. Their eyes, ears and nostrils are located on top of their heads, and they close up when the hippo goes underwater.
A hippo's entire diet consists of several species of grass, and they eat up to 88 pounds (40 kg) of it each night. That's about half as much as other hoofed mammals eat, when you take their body sizes into account, but a hippo's sedentary lifestyle doesn’t require much energy, so it can get by on less food.
Hippos usually gather in groups of about 15 — called bloats, pods or sieges — with a territorial bull that's in charge of the group. During the dry season, though, bigger groups will gather around watering holes. This is actually when most of their breeding takes place, and many baby hippos will be born about eight months later, during the rainy season.
Mothers give birth to a single baby hippo, or calf, either on land or in shallow water. A newborn hippo is relatively small — around 55 to 120 pounds (25 to 54 kg) — and it needs its mom's protection from lions, crocodiles and adult male hippos, which sometimes attack calves in the water.
Hippos usually live to be about 45 years old in the wild.
Where hippos live:
Hippos used to live throughout much of Africa, but now they're mostly confined to protected areas in sub-Saharan Africa. They can be found near rivers, lakes and swamps from Guinea, in western Africa, to Ethiopia, on the eastern side of the continent, and down to South Africa.
Conservation status: Vulnerable
Over the past 10 years there's been a seven to 20 percent decline in the hippo population. Their main threats are illegal poaching for their meat and canine teeth, which are made of ivory, and the loss of freshwater habitats throughout Africa. Experts think there are between 125,000 and 148,000 hippos remaining in the wild.
Odd facts about hippos:
A hippo's hide alone can weigh half a ton.
A recent DNA study found that hippos are closely related to dolphins and whales.
"Hippopotamus" comes from a Greek word meaning "water or river horse."
Hippos have a complex form of communication that relies on grunts and bellows, and some experts think they may even use echolocation. Hippos have an amphibious call that can travel through air and water, and they have good hearing both above and below water.
A hippo's call can reach 115 decibels — about as loud as being near the speakers at a rock concert.
Their ivory canine teeth grow continuously, and reach 20 inches (51 centimeters) in length.
Hippos have adapted to be good swimmers. Membranes between their toes turn their feet into flippers, and fat beneath their skin helps them float in rivers and lakes.
Adult hippos can hold their breath and stay underwater for up to six minutes. Sleeping hippos float up to the surface to breathe.
Hippos can go three weeks without eating, and they can store two days' worth of grass in their stomachs.