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  ScienceZoologyMammalsOrder ArtiodactylaFamily Hippopotamidae


hippopotamusHippopotamus

Hippopotamus amphibius; aka "horse of the river"

Description

The second largest living land animal after the elepants, the hippopotamus is 9-14 feet long, is about 5 feet at the shoulders, and weighs 3,800-9,900 pounds; males are significantly larger than females. It has a huge barrel-shaped body, short legs, and a big, broad head. The body is purple gray or slate above and pale pink beneath, with brownish pink areas around the eyes and ears. The thick skin (which can be up to 1-1/2 inches thick) is covered with very thin hair, except for thick bristle-like hairs on the head and short tail.

Hippos lack scent or sweat glands, but do have mucous glands that secrete a thick oily layer of red pigmented fluid that acts as a sunscreen and may prevent the growth of disease-causing bacteria; the oil is excreted clear, but turns orange-red after a few minutes of to exposure to the sun.

hippo mouthA hippo's jaws can open up to 150 degrees, exposing enormous, sharp incisors and canine tusks that can be up to 20 inches long. The teeth sharpen themselves as they grind together during grazing.

The positions of the eyes, ears, and nostrils allow the hippopotamus to remain mostly submerged but still able to breathe and stay aware of its surroundings. When the animal is completely submerged, the nostrils close and the ears fold to prevent water from entering them. A hippopotamus can easily hold its breath for 5 minutes, and, if necessary, for as long as 15 minutes.

Despite its clumsy appearance, the hippopotamus is actually quite nimble both in the water and on land. The four webbed toes on each hugh foot provide a stable base that allows it to reach speeds of up to 20 miles per hour on land. They also allow it to easily walk along the bottom of the rivers, lakes, and ponds they inhabit. Incredibly buoyant for its size, the hippopotamus can even swim with relative ease.

Hippopotamuses have excellent hearing, sight, and smell.

Distribution and Habitat

Hippopotamuses live in shallow rivers, lakes, and swamps throughout the savanna main river systems of Central Africa. Almost any body of water will do, as long as it is deep enough for the animal to submerge completely and is within 3-5 miles of suitable grazing areas.

Habits and Behaviors

Hippos spend the majority of their day in the water, and emerge at dusk to feed ashore. They will always exit from the water in the same area and travel the same well-trodden paths between water and grazing areas. In fact, the paths they use to get to their grazing grounds often become so worn down over time that they become water-borne gullies during the rainy season.

Hippopotamuses are very social animals, living in herds of 10-20 individuals (up to 100 or more when limited water resources force them to come together in greater numbers). Each herd is comprised of several females and their calves and, typically, one dominant and a few subordinate males. The herd's movements are directed by a dominant female, while the dominant and juvenile males are the chief guards and protectors. While social hierarchies exist in both sexes, they are more important among males than females. Dominant males are very intolerant of young challengers, and may even harm or kill those who don't back down. Males compete for dominance with yawning, roaring, dung showering, and jaw clashing. Each herd will have its own designated water and grazing territory, which is marked with dung and "protected" by wheezing, honking, and dung showering.

Hippos are usually so docile that birds can be seen fishing off their backs while the hippos are submerged, but can become explosively and dangerously aggressive when challenged for dominance or a calf is threatened. The animal's huge jaws can easily snap a canoe in half, and many an unsuspecting person has found that they can inflict a very nasty bite as well.

Hippos are very vocal, both on land and in water. Some vocalizations have been measured at 115 decibels, the equivalent of being 15 feet away from the speakers at a rock concert.

Reproduction

Although breeding can occur any time of the year, it is most common during the dry season, which runs from October through April (depending on specific geographic region). The dominant male of any given herd will attempt to mate with every female in heat, but it is the female that decides whether he will be successful or not. One calf, weighing 50-100 pounds, is born after a gestation period of about 324 days. When ready to give birth, the mother will move away from her herd, and will stay away until her calf is about two weeks old. The calf may be born on land or underwater, and is nursed for about a year. Mother-calf pairs are very affectionate toward each other until the calf reaches sexual maturity, at about 3-1/2 years.

Although hippo calves are small enough to be taken down by lions and other predators, the fact that an entire herd will come to the defense of a single calf makes it very difficult for those predators to succeed. Calf mortality is, therefore, quite low, and a hippopotamus can live up to 55 years in the wild.

Diet

Hippopotamuses feed on small shoots, grasses, reeds, and the occasional fallen fruit. They typically graze four to five hours a night, covering 1-5 miles in the process. Although they travel to grazing areas in groups they feed singly or in mother-calf pairs. The hippo's sedentary lifestyle means it needs far less food relative to body weight than other grazers. Although it may eat up to 100 pounds of vegetation in one night, that is only about 1 to 1-1/2 percent of its total body weight; by comparison, a large cattle typically consumes 2-1/2 percent of its body weight per day. In addition, a hippopotamus can store enough food in its stomach to go as long as three weeks without eating if necessary.

Conservation Status

The hippopotamus is listed as vulnerable due to general habitat loss, hunting, and, in some parts of its range, drought.

Scientific Classification

phylum Chordata
subphylum Vertebrata
class Mammalia
order Artiodactyla
family Hippopotamidae
genus & species Hippopotamus amphibius


African Wildlife Foundation http://www.awf.org/wildlife-conservation/hippopotamus
Animal Diversity Web http://animaldiversity.org/accounts/Hippopotamus_amphibius/
ARKive http://www.arkive.org/hippopotamus/hippopotamus_amphibius/
San Diego Zoo http://animals.sandiegozoo.org/animals/hippo

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  The Robinson Library > Science > Zoology > Mammals > Order Artiodactyla > Family Hippopotamidae

This page was last updated on September 07, 2016.

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