The Mighty Hippopotamus

  • Physical Characteristics

    After the elephant, the common hippo rivals the rhinoceros as the second heaviest land mammal on Earth. Some adult hippos weigh a whopping 7,000 pounds- about the same weight as a large pickup truck!  Hippos have huge heads, short necks and long, barrel-shaped bodies.  They grow up to 15 feet long, but with their short, stumpy legs, common hippos stand only around five feet tall at the shoulders. Their short tails are around 15 inches long.

    The common hippo’s eyes, ears, and nose are high up on its large face.  The position of these features allows it to see hear and breathe while all of its body and most of its head are underwater.  When a hippo goes underwater, its nose and ears close.  It can hold its breath and stay underwater for up to five or six minutes at a time.  As the hippo resurfaces, its nostrils open to exhale and its ears spring back up.  Hippos can sleep in the water because their bodies automatically rise to the surface when they need to breathe.

    Hippos can smell, see, and hear quite well.  Scientists think that hippos are able to communicate with one another both on land and in the water.  They make a variety of sounds that are believed to be different types of messages.

    The common hippo has webbed feet to help it move in the water and broad nails that help it grip the bottoms of rivers and lakes as it walks underwater.  Each foot has four padded toes that support its massive body.  Although the hippo has short legs, it can run faster than a person, make quick turns, and climb steep riverbanks. Hippos don’t even bother stepping over obstacles in their way- they just barrel right through them!

    The common hippo’s skin is smooth and thick.  It is brownish gray to bluish black in color on the top and pinkish on the underside.  The hippo’s skin is well suited for its environment in some ways, but not in others.  Its outer layer of skin absorbs water easily when it’s in the water, which is important in the hot dry African climate. However, the hippo loses much of its moisture through its skin- more, in fact, than any other mammal.  The hippo’s skin is constantly absorbing and losing water.

    Like most other mammals (but unlike humans), hippos don’t sweat to regulate their body temperature.  However, they do produce a sticky pinkish-red fluid, which is thought to moisturize and protect their skin from harmful sun rays.  It was once thought that hippos actually sweated blood!  The liquid is also thought to protect against infection because hippos’ wounds don’t get infected, even in the muddy water of wallows and lakes.

    The common hippo’s mouth is a wonder.  It can open three to four feet wide, nearly 180º!  A hippo has 34 to 36 teeth.  Its tusk-like incisors and canine teeth grow throughout its life but are continually worn down through use.  The lower canine teeth, the largest of its tusk like teeth point upward and can extend 20 inches beyond the gum line!

    The pygmy hippo looks like a young common hippo in size and build, but its legs and neck are proportionately longer.  Its skin is darker than the common hippo’s- greenish-black on top, grey on the sides and even lighter on the underside.  An adult pygmy hippo can weigh up to 604 pounds and reach a height of three feet at the shoulder.  Together, its head and body can reach a length of six feet and its tail is around six inches long.

    The pygmy’s head is smaller than the common hippo’s and its eyes are positioned more to the side of the head.  Like the common hippo, the pygmy’s body is hairless except for the bristles on its mouth, nose, lips, and tail (which is bushier than the common hippo’s).  Like its larger relative, the pygmy produces a sweat like fluid that makes it slick to the touch.  As with the common hippo, the liquid is thought to moisturize and protect its skin from harmful sun rays, as well as prevent infection.


    Only a hippo’s front feet are webbed, and they are not as webbed as the common hippo’s.  Its tusk-like lower canine teeth serve as a weapon and along with its lips, help cut down plants.  Pygmies are also very graceful both on land and in the water.  They, too, have the ability to hold their breath underwater for minutes at a time while walking on the bottom of streams and swamps.

    Foraging and Diet

    At night, common hippos climb out of the water to graze for up to six hours.  They follow paths, called grazing trails, which many of them enter and exit in the same place every night.  These loops, marked by piles of their dung, are usually between two to seven miles long.  The exact purpose of the dung piles isn’t known, but they are thought to help guide the hippo along its nightly grazing path.

    In spite of the hippo’s large mouth and sharp teeth, it mostly eats short land grasses, cropping them with its broad, rough lips.  Sometimes hippos pull out so much grass along the edges of the river that the water erodes the riverbank, and gullies start to form.  Over time these gullies can change the courses of various bodies of water.

    On rare occasions, common hippos eat the duckweed that floats on the water’s surface of dive underwater to reach plants that grow on the river floor.  There have been reports of hippos eating other animals; some tell of hippos killing, and then feeding on a male impala.  But these reports are rare and may be a result of hippos reacting to extreme conditions in their habitat, such as drought.

    During their nightly grazing, common hippos eat anywhere from 88 to 150 pounds of plant matter.  Although this sounds like a lot, it is only about 1% to 1.5% of their body weight.  Many other hoofed animals eat about 2.5 % of their body weight each day.  Hippos don’t need as much food because of their relaxed lifestyle.  Hippos are most active at night during grazing time.  They spend their days sleeping of moving slowly in the water digesting food and getting rid of dung.

    Common hippos stir up their dung while walking along the river bottom.  The dung, because it has the thick consistency of wet hay, provides a good hiding place for insects that don’t want to be seen by their prey.  It is also food for the snails and fish.  These small organisms are then eaten by the larger ones.  Hippos are an important part of the African ecosystem.  When they die in large numbers, the animals that depend on them die, too.

    Pygmy hippos also feed at night along established paths marked by their dung. They eat water plants, fresh leaves from trees, fallen fruits, grasses, herbs, and ferns.  They eat these foods in a variety of ways.  Pygmies graze grasses, strip leaves off branches, and pull swamp plants out of the ground.  To reach high tree branches, they stand on their hind legs and brace themselves on the tree trunk using their forelegs.  Pygmies spend their days hidden in swamps of sometimes in riverbank dens made by other animals that they enlarge for their own use.

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    Vocabulary: characteristics, foraging, grazing,