Nile Hippopotamus

Order: Artiodactyla
Family: Hippopotamidae
Genus and Species: Hippopotamus amphibius

A land animal adapted for an amphibious life, this bulky animal wallows by day and grazes on land by night.

Physical Description: Bulky and barrel-shaped, Nile hippos may look clumsy, but they are supremely adapted to their mixed terrestrial/aquatic lifestyle. Their eyes, ears, and nostrils (which close when the animals submerge) sit atop their heads. They have wide snouts and thick lips for grazing terrestrial grasses. Hippos vary from brown to grayish purple, with pink underparts and skin creases. Their skin consists of a thick dermis (up to 1-3/4 inches thick) covered by thin epidermis that is protected by a red excretion that serves as sunscreen and probably as a disinfectant. Hippos are virtually hairless, with bristles only on their noses, ears, and tails.

Size: Nile hippopotamuses grow up to 15 feet long. Males are heavier than females, weighing up to 8,000 pounds. Nile hippos stand from four and a half to five and a half feet tall.

Geographic Distribution: Nile hippos live only in sub-Saharan Africa. They inhabit rivers, lakes, and wetlands from western African countries like Guinea east to Ethiopia and south to northeastern South Africa.

Status: What had been Africa's second largest population of Nile hippopotamuses—30,000 in the Democractic Republic of the Congo—declined in recent years by 95 percent, due to unregulated hunting for food and ivory. In 2006, the World Conservation Union's (IUCN) Red List of Threatened Species listed Nile hippos as vulnerable.

Habitat: Nile hippopotamuses graze in short grasslands by night and wallow in lakes, rivers, and wetlands by day.

Natural Diet: Several species of grass provide Nile hippopotamuses with virtually all of their food. While they consume up to 88 pounds of grass per night, this amount (about one to one and a half percent of their body weight) is about half that required by other hoofed mammals. Hippos' habit of resting in water during the day reduces energy and food demands.

Reproduction: Female Nile hippopotamuses start breeding at seven to nine years of age, and usually have a single calf every two years. Their gestation period is eight months. Many hippopotamuses are born during the rainy season, following mating that occurs when adults are concentrated in smaller areas during dry months. Males search for females in heat, but must be careful not to be attacked (see Fun Facts). They do not have involved courtship displays. Instead, when a female in heat is found, the male chases her and mates with her.

Life Span: Nile hippopotamuses live up to 45 years in the wild, and often a few years longer in zoos.

Behavior: These animals lead two very different lives. During the day, they congregate in watery areas, resting and sometimes cavorting. Males often face-off (see Fun Facts) and squabble. Sometimes they injure each other, or young hippos, with their long canine teeth. They sometimes also trample young. By night, hippos graze on land alone, except for mothers with attendant young, which feed together. While Nile hippos are usually sluggish on land, they can gallop at up to 30 miles per hour. Underwater, they are graceful, "galloping" and walking on river or lake bottoms.

Past/Present/Future: Nile hippopotamuses were once common throughout sub-Saharan Africa, wherever there was enough water for wallowing and grass for grazing. Hunting (for meat as well as teeth) and habitat loss have combined to reduce many populations.
In some areas, hippos confined to certain parks have overpopulated these areas, causing erosion and the disappearance of certain grasses. Wetland protection, pollution control, and hunting restrictions can ensure a bright future for these large animals.

A Few Nile Hippopotamus Neighbors:

Red-billed oxpecker (Buphagus erythrorhynchus): A starling relative specialized at picking ticks and other parasites off of hippos and other large African animals.

Nile crocodile (Crocodylus niloticus): Growing ten feet or longer, this stealthy reptile ambushes large animals while they drink at the river's edge.

African buffalo (Syncerus caffer): Massive wild cattle that travel the savanna in herds, never far from water.

Fun Facts:
Male Nile hippopotamuses square off at territory boundaries and perform a messy ritual: They turn backside to backside and shower each other in urine and feces—broadcasted with the help of their paddling tails—before walking away from each other.

Because males pose a threat to youngsters, female hippopotamuses attack males that wander too close. If a female begins to attack a male, he lies down and acts submissively to show that he means no harm.

Adult hippos can stay underwater for up to five minutes. Sleeping hippopotamuses can rise to the water's surface to breathe.

Further Reading:

Hippopotamus, by Lynn M. Stone; The Rourke Book Co., Inc., 1990.

The Behavior Guide to African Mammals, by Richard Despard Estes; University of California Press, 1991, pages 222 to 226.

Copyright 1999, Friends of the National Zoo.