Why the hippopotamus is called the river horse

One Earth’s “Species of the Week” series highlights an iconic species that represents the unique biogeography of each of the 185 bioregions of the Earth.

The name Hippopotamus (Hippopotamus amphibius) derives from the Greek term for “river horse.” Indeed, hippos enjoy freshwater habitats like no other land mammal because of their semi-aquatic nature. They can be found in lakes, swamps, and slow-flowing rivers throughout savannas and grasslands in West, Central, East, and South Africa.

Hippos benefit from spending the day in waterways for a number of reasons: their delicate, hairless skin stays hydrated –which adds to the viscous effect of a reddish secretion that gives their skin a pink to purple hue. Also, their permanence in the water and mud helps release the stress of the body weight from their legs, which, though short, impulse the bulky bodies forward when the webbed feet push off the riverbed. Another feature related to their semi-aquatic condition is their eyes, ears, and nostrils, which are high on the roof of the skull, so they are able to be near-to-fully submerged while in the water in the daytime.

To avoid the heat and risk of dehydration, they walk out of the water only when the Sun is down and graze pastures throughout the night. When walking on land, their short legs can stand the weight thanks to their four evenly spread toes. They will cover large extensions of land, walking some 3 km away from the river banks, climbing up steep river banks if necessary, and getting to consume between 60kg and 100 kg of grass in a single night.

Huge features

While female hippos weigh no more than 1500 kilograms, male hippos can reach more than double that. They average 3.5 meters (11 feet) in length and 1.5 meters (5 feet) tall at the shoulder. Their size is approximately the same as the White Rhinoceros, considered the second largest megafauna after Elephants. Male hippos appear to continue growing throughout their lives, whereas female hippos reach a maximum weight at around the age of 25 years.

There are five subspecies of Hippopotamus amphibious, each of which has adapted to a particular bioregion within the African continent. The distinctive features of the Hippo in Zambia, Hippopotamus amphibius capensis, is its very flattened skull.

Their huge mouths have 2 feet-wide lips that can open 150 degrees or 4 feet wide, and their large tusk-like canine teeth are fearsome, and have such force that they can crush a 10-foot crocodile in half.

Hippos in the Creation Story

When God was giving each animal a place in the world, the pair of hippos begged to be allowed to live in the cool water that they so dearly loved. God looked at them, and was doubtful about letting them live in the water: their mouths were so large, their teeth so long and sharp, and their size and appetites were so big, He was afraid that they would eat up all the fish. Besides, He had already granted the place to another predator – the crocodile. He couldn’t have two kinds of large, hungry animals living in the rivers. So God refused the hippos’ request and told them that they could live out on the open plains. At this news, the two hippos began to weep and wail, making the most awful noise. They pleaded and pleaded with God, who finally gave in. But He made the hippos promise that if they lived in the rivers, they must never harm a single fish. They were to eat grass instead. God said that they were to show Him every night, that they were only eating grass. The Hippos promised solemnly, and rushed to the river, grunting with delight.

And to this day, hippos always scatter their dung on the river bank, so God can see that it contains no fish bones. And you can still hear them laughing with joy that they were allowed to live in the rivers after all. (From When the Hippos were Hairy and Other Tales from Africa by Nick Greaves).

Social Behavior

Hippos are typically calm at night, while becoming considerably aggressive at day, especially when intruders show up in the stretch of water that they are occupying. Hippos have a very distinctive performance around potential offenders. Dominant males mark their territory by showering their dung around with their tails, warning other bulls to keep away. Vigilant female hippos will ‘yawn’ to show that are ready to defend their young.

Hippos enjoy living in herds, and the number of individuals can range anywhere between 10 and over 100. The dominant male is the single one expected to mate with females of the herd, although sometimes a subordinate male will be allowed to mate as well.

Coexisting with Hippos

Hippos are plentiful in Zambia’s many waterways, and often groups of over 60 can be seen in one spot, especially along the Luangwa River where the official count is 48 per km².

Above the Luangwa Valley on the plateau watersheds, land is being cleared for people to plant crops like cotton and tobacco, resulting in runoff that silts up in the Luangwa River and waterholes, reducing the habitat for the hippo population. The Wildlife Conservation Society has targeted the conservation of hippos and other wildlife in Zambia through a program where former poachers, who were diminishing animal populations, including hippos and elephants, receive training in organic farming, carpentry, bee-keeping, and ecotourism. The implementation of cooperative methods by local people reduces conflicts with wildlife, thus building a more hopeful future for Africa’s wild animals.