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Last updated on April 18, 2014 at 21:21 EDT

Pygmy Hippopotamus, Choeropsis liberiensis or Hexaprotodon liberiensis

The pygmy hippopotamus (Choeropsis liberiensis or Hexaprotodon liberiensis), also known as the pygmy hippo, is native to western areas of Africa. Its range includes Liberia, with smaller populations occurring in Ivory Coast, Sierra Leone, and Guinea. It prefers a habitat in swamps and forests, where a body of water is available to keep its skin moisturized. It is a semi-aquatic creature, and can perform tasks such as breeding or giving birth in the water or on land.

The pygmy hippo is classified in the genus Choeropsis that means, “Resembling a hog”. It is thought that the Malagasy pygmy hippopotamus, which is now among the three extinct species that inhabited Madagascar, was a sister species to the pygmy hippo, deriving from the same ancestor. Samuel G. Morton once classified the pygmy hippo as Hippopotamus minor, but studies showed that it was unique enough to hold its own genus, Choeropsis. Coryndon suggested that the pygmy hippo was a close relative of prehistoric hippos that were native to Asia, called Hexaprotodon. After Coryndon made this assumption in 1977, it was majorly accepted until 2005, when Boisserie claimed that it was too distinct from Hexaprotodon, and so the pygmy hippo was re-classified into its genus Choeropsis.

Although it has not been completely proven, the pygmy hippo held a distinct subspecies known as the Nigerian pygmy hippopotamus. This possibly extinct subspecies held a range that included the Niger River Delta, with large numbers occurring near Port Harcourt, although records existing today do not support this. It was named after I. R. P. Heslop, who shot one individual and gave a few skulls to the British Museum of Natural History. Heslop estimated that there were only about thirty individuals left of this subspecies at that time. The skulls were not studied until 1969, when G. B. Corbet found that they represented a distinct subspecies.

It was thought that both the pygmy hippopotamus and its larger relative, the common hippopotamus, were most closely related to hogs or pigs in the Suidae family, or peccaries. Due to research done in the past ten years, it is now commonly thought that hippos are more closely related to dolphins or whales. It is thought that hippos originated from Africa, and although they moved through Europe and Asia, no native specimens have been found in the Americas.

There were many species of smaller hippos that once inhabited the Mediterranean, but these are now extinct. Among these species are the Sicilian hippopotamus, the Maltese hippopotamus, the Cretan dwarf hippopotamus, and the Cyprus dwarf hippopotamus. These species are considered to be dwarf hippos, because they were larger than pygmy hippos but smaller than hippopotamuses. It is thought that their small size occurred due to living on islands, a frequent occurrence among island dwelling animals.

The pygmy hippopotamus resembles its large relative closely, with short legs and a stout body, however, this species is about half as small as its cousin is. The pygmy hippo reaches an average body length of 5.8 feet, a height of 2.6 feet at the shoulders, and an average weight between four hundred and six hundred pounds. Its skin can be green-black in color, or brown, with a light creamy colored underbelly. Like the large hippopotamus, the pygmy hippo secretes a pinkish colored substance, known as “blood-sweat”, although it is neither sweat nor blood. It is thought that this secretion holds a mixture of sun screening and antiseptic properties. This aids the hippos in keeping their dry skin moist.

Because the pygmy hippo is smaller than the common hippopotamus, its bones are thinner, which give it a better level of gracefulness. The pygmy hippo’s spine differs from that of the hippopotamus, curving forward at a sloping angel, and it is thought that this aids its movement through dense vegetation. The pygmy hippo spends less time in the water than its larger relative, and so its nostrils and eye sockets are less adapted to keeping water out. The toes are also adapted for moving through forest vegetation, bearing toes that are more spread out and with less webbing than the toes of the common hippopotamus. Despite these adaptations that aid on land, the pygmy hippo is the most aquatic of all even-toed ungulates.

The pygmy hippo is reclusive, but it will live in small groups containing one male, one female, and a calf or just a mother and a calf. Instead of aggressively attacking each other, when pygmy hippos have an encounter, they tend to ignore each other. Studies have shown that males of this species can hold a home range of over 460 acres, while females hold smaller ranges between 99 and 150 acres. These hippos can be seen resting in the same area of water for most of their day, choosing a new spot every few days. These hippos may use burrows and dens created in riverbanks, but it is not known whether the hippos help create these homes.

There have been no studies on the reproductive habits of wild pygmy hippos, so results from studies conducted with these hippos in captivity may not represent wild individuals. In captivity, males and females will join as one monogamous pair, and can mate in the water or on land, however, the length of the relationship between the male and female is unknown. The pair can breed year-round. Young are born after 190 to 210 days, with litters typically containing one baby, although twins do occur.

Baby pygmy hippos weigh between 9.9–13.7 pounds at birth, and are able to swim almost immediately after birth. Instead of following the mother out of the water, the baby pygmy hippo will remain hidden in the water for safety as she forages for food. The baby will nurse up to three times a day and is weaned at six to eight months of age. The average age at which the pygmy hippo reaches sexual maturity is between three and five years of age.

The diet of the pygmy hippo consists of fallen fruits, ferns, and broad-leaves. It rarely eats grasses or aquatic vegetation. It will eat a large variety of plants, giving it a higher quality of food in its diet. Like its larger relative, the pygmy hippo comes out of the water at dusk to forage for food, using trails to move through the forest. These trails are created when the hippo uses its feces to scent mark the area.

Unlike the common hippopotamus, the pygmy hippo was not known outside of its range until the 19th century. In Liberia, it was known as the water cow. Early reports of this species described it as a wild hog. The first captured individual, from Sierra Leone, was taken to Europe by a British Colonial Service member, but it did not live long after its arrival. It was not until 1911 that the pygmy hippo was successfully introduced into Europe. Some of these European individuals were shipped to Germany and to the Bronx Zoo in New York after that.

There are a large number of pygmy hippos in U.S. zoos today, and it is know that many of these individuals share the same ancestor, called Billy the pygmy hippo. This hippo was given to President Calvin Coolidge as a gift from Harvey Firestone of Firestone Tires. These hippos have been the focus of a few folk tales, including one that says they carry a bright diamond in their mouths in order to help them travel through the forest at night. The tale suggested that hunters could take the diamond only at night. It was also said that baby pygmy hippos did not nurse, but rather licked the secretions of “blood-sweat” off their mothers for food.

The pygmy hippo is threatened by habitat loss due to logging, farming practices, and human settlement. These factors cause fragmentation in viable habitat, which leads to a decrease in genetic diversity. It is not threatened by game hunters, but bush meat hunters do find it to have a superb quality of meat. It is not known how civil war in Africa has affected the pygmy hippo, but it is thought to have had a negative impact on its population numbers. Its natural predators include pythons, crocodiles, and leopards, although there are no records that state how often these animals hunt the pygmy hippo.

In captivity, the populations of pygmy hippos are increasing, causing the survival of the species in in zoos to be higher than the chances of wild pygmy hippos surviving. The number of births in zoos doubled between the years of 1970 and 1991, but only nineteen percent of births in captivity since 1919 have been males. The Zoo Basel, located in Switzerland, oversees the breeding of pygmy hippos around the world, holding the international studbook of breeding males. There are some wild populations that can be found in protected areas, and the species was listed as a “focal species” by the Evolutionarily Distinct and Globally Endangered (EDGE) project in 2007. The pygmy hippopotamus appears on the IUCN Red List with a conservation status of “Endangered”.

Image Caption: Pygmy hippo / pygmy Hippopotamus. Credit: Tomasz Sienicki/Wikipedia  (CC BY 2.5)

Pygmy Hippopotamus Choeropsis liberiensis or Hexaprotodon