Hippopotamuses (Hippopotamus amphibius) are large, round, water-loving animals that are native to Africa. The word "hippopotamus" comes from the Greek word for "water horse" or "river horse," although hippos and horses aren't closely related. The closest living relatives to hippos are pigs, whales and dolphins, according to the San Diego Zoo.

Size

Common hippos, also known as river hippos, are very rotund animals and are the third largest living land mammals, after elephants and white rhinos, according to the African Wildlife Foundation. They grow to between 10.8 and 16.5 feet (3.3 and 5 meters) long and up to 5.2 feet (1.6 m) tall at the shoulder. The average female weighs around 3,000 lbs. (1,400 kilograms), while males weigh 3,500 to 9,920 lbs. (1,600 to 4,500 kg), according to the San Diego Zoo.

These enormous animals are related to the much smaller and rarer pygmy hippo (Choeropsis liberiensis), which only grows to be 2.5 to 3.2 feet (0.75 to 1 m) tall and about 5 to 6 feet (1.5 to 1.75 m) long, according to the San Diego Zoo. Pygmy hippos can weigh between 350 and 600 lbs. (160 and 270 kg).

Habitat and behavior

Common hippos live in sub-Saharan Africa. They live in areas with abundant water, as they spend most of their time submerged to keep their skin cool and moist. Considered amphibious animals, hippos spend up to 16 hours per day in the water, according to National Geographic.

Hippos are social beasts, hanging out in groups called schools, bloats, pods or sieges. Schools of hippos usually consist of 10 to 30 members, including both females and males, although some groups have as many as 200 individuals. No matter the size, the school is usually led by a dominant male, according to the San Diego Zoo.

Hippos are loud animals. Their snorts, grumbles and wheezes have been measured at 115 decibels, according to the San Diego Zoo — about the same volume you'd hear when 15 feet (4.6 m) from the speakers at a rock concert. The animals' signature noise, called the "wheeze honk," can be heard from more than half a mile (1 kilometer) away, Live Science previously reported. These booming creatures also use subsonic vocalizations to communicate.

Hippos are aggressive and are considered very dangerous. They have large teeth and tusks that they use for fighting off threats, including humans. Sometimes, their young fall victim to adult hippos' tempers. During a fight between two adults, a young hippo caught in the middle can be seriously hurt or even crushed, according to PBS.

Though hippos move easily through the water, they can't actually swim. According to the San Diego Zoo, these animals glide through the water by pushing themselves off other objects. And they can stay underwater for up to 5 minutes without coming up for air, according to National Geographic.

(Image credit: Andreas Lippenberger/Shutterstock)

Hungry, hungry hippos

Hippos have a healthy and mostly herbivorous appetite. Adults eat about 80 lbs. (35 kg) of grass each night, traveling up to 6 miles (10 km) in a night to get their fill. They also eat fruit that they find during their nightly scavenging, according to National Geographic. If food is scarce, hippos can store food in their stomachs and go up to three weeks without eating.

Although hippos were long believed to be exclusively herbivorous, in a 2015 study published in the journal Mammal Review, scientists reported that hippos occasionally feed on the carcasses of animals, including other hippos.

Baby hippos

Female hippos have a gestation period of eight months and have only one baby at a time, according to the San Diego Zoo. At birth, the calf weighs between 50 and 110 lbs. (23 and 50 kg). For its first eight months, the calf nurses while its mother is on land, or it swims underwater to suckle. When it dives, the calf closes its nose and ears to block out water. All hippos have this ability. Hippos also have membranes that cover and protect their eyes while they are underwater.

At 5 to 7 years old, a hippo calf is fully mature, according to the San Diego Zoo. The average life span of a hippo in the wild or in captivity can range from about 40 to 61, according to the University of Michigan's Animal Diversity Web.

Related: What animal has the longest pregnancy?

Attacks on humans

The hippopotamus is considered the world's deadliest large land mammal. These semiaquatic giants kill an estimated 500 people per year in Africa, according to the BBC. Hippos are highly aggressive and are well-equipped to deliver considerable damage to anything that wanders into their territory.

For example, in 2014, a hippo attacked a small, unsuspecting boat filled with Nigerian school children, killing 12 students and one teacher on board, ABC News reported. Conflicts between humans and hippos also occur when hippos wander onto land in search of food.

Hippos have big teeth. Don't mess with them. (Image credit: Shutterstock)

Conservation status

According to the International Union for Conservation of Nature (IUCN), the common hippo isn't endangered, but it is vulnerable to extinction. The IUCN estimates that between 115,000 and 130,000 common hippos remain in the wild. Poaching and habitat loss reduced the hippo's global numbers during the late 1990s and early 2000s, but the population has since plateaued thanks to stricter law enforcement, according to the IUCN.

Invasive hippos

Notorious drug lord Pablo Escobar famously kept hippos, giraffes, elephants and other exotic animals on his estate in northwestern Colombia. When Escobar was killed in 1993, the Colombian government seized all of his assets, including his menagerie. Most of his animals were transferred to zoos and aquariums, but his four hippos were left to fend for themselves. Those four animals made their way into Colombia's waterways, where they multiplied.

An estimated 80 hippos now inhabit the river networks near Medellín, Colombia, where Escobar's Hacienda Nápoles estate was located, Live Science reported in October 2021. Wildlife officials in Colombia began sterilizing the hippos in 2021, because this invasive population poses a threat to the community, in that the massive beasts occasionally trample crops and charge at humans. The hippos also threaten native wildlife populations and their presence degrades the local ecosystem, as each individual hippo gobbles down dozens of pounds of vegetation a night and generates formidable quantities of poop.

However, many Colombians have grown fond of the uninvited ungulates and vehemently oppose their removal. Some scientists, though, fear that the animals' continued presence could have unintended consequences. "The risk to native species — such as manatees, turtles and fish — is high, and the environmental effect is unpredictable," Nelson Aranguren-Riaño, biologist at Pedagogical and Technological University of Colombia, said in a statement.

Additional resources and readings

Did you know hippos are covered in mucus? Learn more with SciShow Kids. Learn about the "The 'Beauty' Regime of Hippos" with BBC Earth. Check out the book Saving Fiona: The Story of the World's Most Famous Baby Hippo.

Bibliography

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African Wildlife Foundation. (n.d.). Hippopotamus. African Wildlife Foundation. Retrieved February 4, 2022, from https://www.awf.org/wildlife-conservation/hippopotamus

BBC. (2016, June 15). What are the world's deadliest animals? BBC News. Retrieved February 4, 2022, from https://www.bbc.com/news/world-36320744

Dudley, J. P., Hang'Ombe, B. M., Leendertz, F. H., Dorward, L. J., Castro, J., Subalusky, A. L., & Clauss, M. (2015). Carnivory in the common hippopotamus Hippopotamus amphibius: implications for the ecology and epidemiology of anthrax in African landscapes. Mammal Review, 46(3), 191–203. https://doi.org/10.1111/mam.12056

IUCN. (n.d.). Hippopotamus. IUCN Red List of Threatened Species. Retrieved February 4, 2022, from http://www.iucnredlist.org/details/10103/0

National Geographic. (n.d.). Hippopotamus: National Geographic. National Geographic. Retrieved February 4, 2022, from https://www.nationalgeographic.com/animals/mammals/facts/hippopotamus

Public Broadcasting Service. (2020, July 9). Hippo fact sheet. PBS. Retrieved February 11, 2022, from https://www.pbs.org/wnet/nature/blog/hippo-fact-sheet/

San Diego Zoo. (n.d.). Hippo. San Diego Zoo Wildlife Alliance Animals and Plants. Retrieved February 4, 2022, from https://animals.sandiegozoo.org/animals/hippo

San Diego Zoo. (n.d.). Pygmy hippopotamus. San Diego Zoo Wildlife Alliance Animals and Plants. Retrieved February 4, 2022, from https://animals.sandiegozoo.org/animals/pygmy-hippopotamus

UC San Diego. (2018, April 26). A drug lord and the world's largest invasive animal. UC San Diego News Center. Retrieved February 4, 2022, from https://ucsdnews.ucsd.edu/feature/a-drug-lord-and-the-worlds-largest-invasive-animal

This article was last updated on Feb. 14, 2022 by Live Science staff writer Nicoletta Lanese. Live Science contributor Annie Roth also contributed reporting.

Originally published on Live Science.