Hippopotamus
Hippopotamus
The hippo’s teeth and its diet
The common or river hippopotamus (Hippopotamus amphibius) is a huge, even-toed hoofed herbivore that lives in bodies of freshwater in central and southern Africa. A second species, the pygmy hippopotamus (Hexaprotodon liberiensis ), lives in water bodies in West African rainforests. Both species are included in the family Hippopotamidae.
The name hippopotamus means “river horse” but hippos are only distantly related to horses. Horses are odd-toed hoofed animals, while hippos are even-toed in the class Artiodactyla. Hippos have four hoofed toes on each foot. The common hippo has webbing between its toes, while the pygmy hippo has less webbing.
Fossil finds indicate that hippos were formerly found throughout much of Eurasia, but today hippos are found only in the tropical regions of Africa. The common hippo is abundant in the rivers, lakes, and swamps of most of sub-Saharan Africa, while the pygmy hippo is limited to forested areas in West Africa.
The common hippo
The common hippo is barrel-shaped, measuring 14 ft (4 m) long, 4.5 ft (1.5 m) high and weighing about 2 tons (1,800 kg). Large males have been known to reach 4.5 tons (3,800 kg). The common hippo is slate brown in color, shading to either a lighter or darker color on the underside.
Common hippos have relatively short legs for their vast girth, but hippos spend most of the day under water, with only the top of their head visible. Their eyes are sited on top of their head, and sometimes only the eyes, the flicking ears, and a small mound of back are all that is visible.
The hippo’s teeth and its diet
Hippos have a huge mouth, measuring up to 4 ft (1.2 m) across, and a pair of huge incisors in each jaw. Only a few teeth are immediately visible, mainly the curved lower canine teeth (which are a source of ivory) on the outer part of the jaw. Like tusks, these teeth continue to grow and can reach a length of 3 ft (1 m). Hippos are herbivores, grinding up vegetation with their big, flat molars at the back and the mouth. Hippos die when their molars have worn down too much to grind food.
After sunset, hippos come onto land in search of succulent grasses and fruits. The path to an individual bull’s foraging ground may be marked by a spray of excrement that warns other hippos away. The cows do not mark their paths. Individual animals may wander as far as 20 mi (32 km) during the night to find food. It takes almost 150 lb (68 kg) of food each night to satisfy a hippo’s appetite.
Hippo in water
A hippo’s eyes, ears, and nostrils are all positioned in a single plane that can stay above water when the rest of the animal is submerged. Both the ears and the nostrils can close, at least partially, when in water. Hippos do not see well either on land or in the water; instead, they depend on their acute hearing to warn them of danger and their good sense of smell to find food. When alarmed, a hippo may quietly submerge or it may attack, especially if it is threatened by people in boats. Several hundred people are killed by hippos each year in Africa.
Hippos spend most of the day in groups in the water. They prefer water about 5 ft (1.5 m) deep, just deep enough to swim if they want to or to walk on the bottom. Hippos can stay completely submerged for about six minutes, but they generally rise to breathe again after only two or three minutes. They can control the rate of their rising and sinking in the water by changing the volume of air in their lungs by movements of the diaphragm. Hippos can walk on the bottom of the river or lake at a rate of about 8 mi (13 km) per hour. On land, they can run at up to 20 mi (32 km) an hour.
Reproduction
A single herd of hippos may include up to 100 animals. The herd’s location, foraging, and movement are controlled by a group of mature females. The females and their young inhabit the center of a herd’s territory, called the crèche. The male’s individual territories, called refuges, are spaced around the crèche. A bull will defend his territory against another bull. If roars and open mouths do not scare off the challenger, they attack each other with open mouths, trying to stab their canine teeth into each other’s head or heart.
The animals breed as the dry season is ending, with the females selecting their mates. Hippos mate in water. Gestation lasts about eight months, and the calves are occasionally born in the water at the height of the rainy season when the most grass is available. A new calf is about 3 ft (1 m) long and weighs about 60 lb (27 kg) when born. On land, it can stand very quickly. It will be several weeks, however, before the mother and her infant rejoin the group.
Once taken into the crèche, the young hippos are tended by all the females. Although adult hippos have few enemies, the calves are small enough to be taken by lions and crocodiles. Until young hippos start to swim by themselves, the young may ride on their mothers’ backs when in the water. Once they can swim, the calves may nurse, eat, and even nap under water. They automatically come up to the surface to breathe every few minutes.
Young females are sexually mature at three to four years old, but usually do not mate until they are seven or eight years old. Male hippos are mature at about five years old, but do not successfully challenge the dominant males for the right to mate until they are much older. A cow with a young calf will usually have another calf when the first one is two or three years old. Because an adolescent hippo is not ready to go out on its own until about four years of age, a cow may be taking care of two calves at once. In the wild, hippos live for about 30 years, while in captivity they can live past 40 years old.
KEY TERMS
Crèche —The central group in a herd of hippos, including mature females and calves.
The pygmy hippo
Pygmy hippos were discovered relatively recently in 1913, when an agent for a German animal collector caught several specimens and sent them back to Europe. The smaller pygmy hippo is proportioned more like a pig than the common hippo. Pygmy hippos reach a height of only about 3 ft (1 m), a length of 5 ft (1.5 m), and weigh only about 500 lb (227 kg). The oily black skin has a greenish tinge, with lighter colors, even yellow-green, on its underparts.
Unlike the common hippo, the pygmy hippo’s eyes do not bulge out and it has only one set of incisors. The skin contains glands that secrete an oil that looks reddish in sunlight, a characteristic which prompted sideshow claims that the pygmy hippo sweated blood. The oil probably acts as a sunscreen and is also thought to have antiseptic properties. Pygmy hippos’ skin dries out very easily, so they live within an easy stride of water. Pygmy hippo calves are born after a seven month gestation, weigh less than 10 lb (4.5 kg), and have to be taught to swim.
Hippos and people
Hippos herds greatly benefit the rivers and lakes where they live, their excrement fertilizing the vegetation of the habitat. As a result, all animals in the food chain benefit, and fishing is usually very good in hippo areas. When the supply of nearby vegetation in areas near hippo pools became scarce, however, these huge animals sometimes feed in farm fields, where many have been shot. Also, hippos are hunted for their meat, hide, and ivory tusks.
The numbers of pygmy hippos left in the wild is uncertain because they are so rarely seen, but it is likely that they are an endangered species due to habitat degradation and hunting pressure. Luckily, pygmy hippos breed well in zoos, and it may one day be possible to restock the wild habitats.
Resources
BOOKS
Arnold, Caroline. Hippo. New York: Morrow Junior Books, 1989.
Green, Carl R., and Sanford, William R. The Hippopotamus. Wildlife Habits & Habitats Series. New York: Crestwood House, 1988.
Knight, Linsay. The Sierra Club Book of Great Mammals. San Francisco: Sierra Club Books for Children, 1992.
Nowak, Ronald M. Walker’s Mammals of the World. 6th ed. Baltimore: The Johns Hopkins University Press, 1999.
Stidworthy, John. Mammals: The Large Plant-Eaters. Encyclopedia of the Animal World. New York: Facts On File, 1988.
Jean F. Blashfield
Hippopotamus
Hippopotamus
The common or river hippopotamus (Hippopotamus amphibius) is a huge, even-toed hoofed herbivore that lives in bodies of freshwater in central and southern Africa . A second species , the pygmy hippopotamus (Choeropsis liberiensis), lives in water bodies in Western African rainforests. Both species are included in the family Hippopotamidae.
The name hippopotamus means "river horse" but hippos are only distantly related to horses . Horses are odd-toed hoofed animals, while hippos are even-toed in the class Artiodactyla. Hippos have four hoofed toes on each foot. The common hippo has webbing between its toes, while the pygmy hippo has less webbing.
Fossil finds indicate that hippos are formerly found throughout much of Eurasia, but today hippos are found only in the tropical regions of Africa. The common hippo is abundant in the rivers , lakes, and swamps of most of sub-Saharan Africa, while the pygmy hippo is limited to forested areas in West Africa.
The common hippo
The common hippo is barrel-shaped, measuring 14 ft (4 m) long, 4.5 ft (1.5 m) high and weighing about 2 tons (1,800 kg). Large males have been known to reach 4.5 tons (3,800 kg). The common hippo is slate brown in color , shading to either a lighter or darker color on the underside.
Common hippos have relatively short legs for their vast girth, but hippos spend most of the day under water, with only the top of their head visible. Their eyes are sited on top of their head, and sometimes only the eyes, the flicking ears, and a small mound of back are all that is visible.
The hippo's teeth and its diet
Hippos have a huge mouth, measuring up to 4 ft (1.2 m) across, and a pair of huge incisors in each jaw. Only a few teeth are immediately visible, mainly the curved lower canine teeth (which are a source of ivory) on the outer part of the jaw. Like tusks, these teeth continue to grow and can reach a length of 3 ft (1 m). Hippos are herbivores, grinding up vegetation with their big, flat molars at the back and the mouth. Hippos die when their molars have worn down too much to grind food.
After sunset, hippos come onto land in search of succulent grasses and fruits . The path to an individual bull's foraging ground may be marked by a spray of excrement that warns other hippos away. The cows do not mark their paths. Individual animals may wander as far as 20 mi (32 km) during the night to find food. It takes almost 150 lb (68 kg) of food each night to satisfy a hippo's appetite.
Hippo in water
A hippo's eyes, ears, and nostrils are all positioned in a single plane that can stay above water when the rest of the animal is submerged. Both the ears and the nostrils can close, at least partially, when in water. Hippos do not see well either on land or in the water; instead, they depend on their acute hearing to warn them of danger and their good sense of smell to find food. When alarmed, a hippo may quietly submerge or it may attack, especially if it is threatened by people in boats. Several hundred people are killed by hippos each year in Africa.
Hippos spend most of the day in groups in the water. They prefer water about 5 ft (1.5 m) deep, just deep enough to swim if they want to or to walk on the bottom. Hippos can stay completely submerged for about six minutes, but they generally rise to breathe again after only two or three minutes. They can control the rate of their rising and sinking in the water by changing the volume of air in their lungs by movements of the diaphragm. Hippos can walk on the bottom of the river or lake at a rate of about 8 mi (13 km) per hour. On land, they can run at up to 20 mi (32 km) an hour.
Reproduction
A single herd of hippos may include up to 100 animals. The herd's location, foraging, and movement are controlled by a group of mature females. The females and their young inhabit the center of a herd's territory, called the crèche. The male's individual territories, called refuges, are spaced around the crèche. A bull will defend his territory against another bull. If roars and open mouths do not scare off the challenger, they attack each other with open mouths, trying to stab their canine teeth into each other's head or heart .
The animals breed as the dry season is ending, with the females selecting their mates. Hippos mate in water. Gestation lasts about eight months, and the calves are occasionally born in the water at the height of the rainy season when the most grass is available. A new calf is about 3 ft (1 m) long and weighs about 60 lb (27 kg) when born. On land, it can stand very quickly. It will be several weeks, however, before the mother and her infant rejoin the group.
Once taken into the crèche, the young hippos are tended by all the females. Although adult hippos have few enemies, the calves are small enough to be taken by lions and crocodiles . Until young hippos start to swim by themselves, the young may ride on their mothers' backs when in the water. Once they can swim, the calves may nurse, eat, and even nap under water. They automatically come up to the surface to breathe every few minutes.
Young females are sexually mature at three to four years old, but usually do not mate until they are seven or eight years old. Male hippos are mature at about five years old, but do not successfully challenge the dominant males for the right to mate until they are much older. A cow with a young calf will usually have another calf when the first one is two or three years old. Because an adolescent hippo is not ready to go out on its own until about four years of age, a cow may be taking care of two calves at once. In the wild, hippos live for about 30 years, while in captivity they can live past 40 years old.
The pygmy hippo
Pygmy hippos were discovered relatively recently in 1913, when an agent for a German animal collector caught several specimens and sent them back to Europe .
The smaller pygmy hippo is proportioned more like a pig than the common hippo. Pygmy hippos reach a height of only about 3 ft (1 m), a length of 5 ft (1.5 m), and weigh only about 500 lb (227 kg). The oily black skin has a greenish tinge, with lighter colors, even yellow-green, on its underparts.
Unlike the common hippo, the pygmy hippo's eyes do not bulge out and it has only one set of incisors. The skin contains glands that give off an oil that looks reddish in sunlight, a characteristic which prompted sideshow claims that the pygmy hippo sweated blood . The oil keeps the animal's skin from drying out. Pygmy hippos' skin dries out very easily, so they live within an easy stride of water. Pygmy hippo calves are born after a seven month gestation, weigh less than 10 lb (4.5 kg), and have to be taught to swim.
Hippos and people
Hippos herds greatly benefit the rivers and lakes where they live, their excrement fertilizing the vegetation of the habitat . As a result, all animals in the food chain benefit, and fishing is usually very good in hippo areas. When the supply of nearby vegetation in areas near hippo pools became scarce, however, these huge animals sometimes feed in farm fields, where many have been shot. Also, hippos are hunted for their meat, hide, and ivory tusks.
The numbers of pygmy hippos left in the wild is uncertain because they are so rarely seen, but it is likely that they are an endangered species . Luckily, pygmy hippos breed well in zoos, and it may one day be possible to restock the wild habitats.
Resources
books
Arnold, Caroline. Hippo. New York: Morrow Junior Books, 1989.
Green, Carl R., and William R. Sanford. The Hippopotamus. Wildlife Habits & Habitats Series. New York: Crestwood House, 1988.
Hippos. Zoobooks Series. San Diego: Wildlife Education, 1988.
Knight, Linsay. The Sierra Club Book of Great Mammals. San Francisco: Sierra Club Books for Children, 1992.
Lavine, Sigmund A. Wonders of Hippos. New York: Dodd, Mead & Company, 1983.
Stidworthy, John. Mammals: The Large Plant-Eaters. Encyclopedia of the Animal World. New York: Facts On File, 1988.
Jean F. Blashfield
KEY TERMS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- Crèche
—The central group in a herd of hippos, including mature females and calves.
hippopotamus
hip·po·pot·a·mus / ˌhipəˈpätəməs/ • n. (pl. hippopotamuses or hippopotami / -mī; -mē/ ) a large thick-skinned semiaquatic African mammal (family Hippopotamidae), with massive jaws and large tusks. Two species: the very large Hippopotamus amphibius and the smaller pygmy hippopotamus (Choeropsis liberiensis).