Animals Wildlife 12 Fun Hippo Facts Why do they spend so much time in the water? Can they swim? By Amy Y. Conry Davis Amy Y. Conry Davis Writer University of San Diego Center for Documentary Studies at Duke University Amy Y. Conry Davis is a writer who specializes in green living, sustainability, and travel. She holds a B.A. in English from the University of San Diego. Learn about our editorial process Updated August 13, 2021 Fact checked by Elizabeth MacLennan Fact checked by Elizabeth MacLennan University of Tennessee Elizabeth MacLennan is a fact checker and expert on climate change. Learn about our fact checking process Share Twitter Pinterest Email GomezDavid / Getty Images Animals Wildlife Pets Animal Rights Endangered Species The hippo (Hippopotamus amphibius) is a semiaquatic mammal found in Africa. It is one of only two species in the family Hippopotamidae: the common or river hippo and the pygmy hippo. The river hippo is the largest of the two and its populations are concentrated in sub-Saharan Africa. The pygmy hippo, native of West Africa, is a solitary, nocturnal creature that lives in forested areas and survives on an herbivorous diet of grasses and leaves. Both species require the cooling, restorative powers of muddy waters and rivers and spend a large portion of their time with their bodies almost fully submerged. Though their skin appears to be rough and rugged, it's actually very sensitive to the intense sun and needs nearly constant hydration. Whereas the common hippo lives in large groups led by the most dominant male, pygmies prefer to stay on their own or in much smaller groups. 1. Hippos Are One of the Largest Animals on the Planet Winfried Wisniewski / Getty Images Alongside the elephant and rhinoceros, the common hippo is one of the biggest animals on our planet. An average, full-grown male can reach up to 7,000 pounds; that's roughly the weight of a UPS truck! A female will generally weigh in at about 3,000 pounds. A full-grown pygmy hippo, on the other hand, only gets to about 600 pounds. At birth, baby hippos start out at around 60 pounds, but it doesn't take them long to gain weight. In less than 3.5 years, a hippo is considered mature. 2. They Can't Swim Though the Greeks called them "river horses" and you will almost always see hippos in the water, they can't actually swim or float. They will spend hours in rivers and lakes, sometimes with only their eyes showing, but they remain in shallow waters. They find sandy river bottoms and banks to stand on. Most of their foraging activity is done at night, since they're nocturnal animals, but during the heat of the day they have to find a way to protect themselves from the sun of midday. The mud and water act as a barrier to soothe their skin and regulate their temperature. 3. Calves Can Suckle Underwater Manoj Shah / Getty Images Hippos are vegetarians, but during the first year of life hippo calves nurse on milk from their mothers. Once they're born, they stay close to their mothers, relying on them for food until they can survive on their own in the wild. They are even known to ride on their mothers' backs at times. Interestingly, the hippo's body has adapted to allow the calves to nurse both on land and underwater. The eyes and nostrils close to prevent the calf from ingesting water and they can maintain this position for several minutes. Despite internet rumors, hippo milk is not pink. Like most other mammals, their milk is whitish-yellow in color. 4. They Can Hold Their Breath for Up to Five Minutes What hippos lack in swimming skills they more than make up with their ability to hold their breath for long periods of time. A thick membrane covers their eyes and their nostrils close, creating a protective water-tight seal. Hippos will do this when they sense danger or feel threatened by something in their environment. They may move to another area or just stay still until they feel it's safe to come back up to the surface. Strangely enough, hippos are even able to sleep underwater using this same reflexive instinct. 5. Hippos Are Very Vocal Creatures Hippos are very loud and use a series of noises to communicate with one another in their groups. These sounds are quite distinct and have been described as honks, growls, whines, and squeaks. At times, it also resembles the sound of human laughter. On land, it's said their calls can be heard up to a mile away, but hippos have also been known to vocalize underwater. Not much is understood about what each call means or why they do it, but like other animals, it's their way of spreading messages. They could be alerting other hippos to danger, signaling a time to move or stay still, or calling after their young. 6. A Group of Hippos Is Called a Bloat Vittorio Ricci - Italy / Getty Images Pygmy hippos will spend most of their lives in solitary routines, but common hippos are often found in large groups or bloats. At times, these groups can include up to 100 hippos in total. This allows for safety and security and gives males control over their territory and families. The main predators of hippos are large cats, crocodiles, and hyenas. They will often go after the smallest offspring, especially if they've wandered away from the protection of the group. They also look for old and injured hippos that are vulnerable to an attack and unable to defend themselves. 7. Pygmy Populations Are Decreasing MikhailSemenov / Getty Images According to the IUCN Red List, the pygmy hippo is endangered. As of the last assessment in 2015, their populations in Sierra Leone, Liberia, and Cote D'Ivoire were in decline likely due to "human intrusions and disturbance." It's believed that less than 3,000 pygmies are left. This species tends to concentrate in swampy forests, so destruction of habitat or poaching could be contributing to the decrease in their numbers. Common hippo populations are stable, yet they have a vulnerable status on the IUCN list. 8. They Get Sunburnt Sensitive skin is the primary reason hippos spend so much time in the water and away from land. But interestingly, their bodies have been designed to create their own sunscreen of sorts. They have evolved over time to be able to secrete a certain kind of pinkish sweat that covers the length of their bodies. They don't actually have sweat glands, but this oily substance comes from pores in their skin and acts to protect them from sun damage and prevent infection. 9. Female Hippos Are Pregnant for 8 Months Much like a human, female hippos have quite a long gestational period. River hippos are pregnant for about 237 days, which equates to roughly 8 months. For a comparison, the mammal with the longest time is the elephant which is pregnant for over 600 days. Sperm whales come in second at nearly 500 days. Hippos will only have one baby at a time. The calve will remain by its mother's side for nearly a year, suckling milk as it grows and gains strength. After that time, it will quit nursing and feed on vegetation. 10. Hippos Mate in the Water Hippos mate every two years and most of the mating rituals take place in the water. Both males and females use vocalizations, body language, and even their own urine and feces to show their interest (or lack thereof). A male will travel, compete, and fight other males in order to get the mate he wants, so typically only dominant, powerful hippos are allowed to mate successfully. 11. Hippos Are Polygamous Hippos are not known to mate for life and a male may have up to 10 mates in one lifetime. Because it's the dominant male hippo or bull that rules the rest of the group, it's often quite a challenge for younger males to secure a female to breed with. In one season, a male will usually mate with more than one female to ensure offspring. After the calves are born they will all stay together in his territory, where he can protect and shelter them from other competing males and predators. 12. Male Hippos Fling Their Dung to Mark Their Territory One of the reasons why hippos are considered dangerous and unpredictable animals is because of their need to defend their territory. Females will fiercely protect their young, but it's the males who are most vicious and threatening. They will go after any hippo (even family), animal, or human that dares enter their personal space. On land, they may use their tails to fling their feces around the area to show their territory to others. Wide open mouths, loud noises, or charging may also signal that they are defending their land. 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