Pygmy Hippopotamus

About the pygmy hippopotamus

The pygmy hippopotamus is a small hippopotamid native to the forests and swamps of West Africa, found mostly in Liberia, with smaller numbers in Sierra Leone, Guinea, and Ivory Coast. It has been extirpated from Nigeria and possibly from Guinea-Bissau. It belongs to the family Hippopotamidae, in the genus Choeropsis, and is one of only two living species in that family — the other being its much larger relative, the common hippopotamus. The genus name comes from Ancient Greek words for "pig" and "resemblance."

Pygmy hippos share the general body plan of a hippopotamus: a graviportal skeleton, four stubby legs, and four toes on each foot supporting a portly frame. But the pygmy hippo stands only about half as tall as the common hippo and weighs less than a quarter as much. Its skin is greenish-black or brown, shading to a creamy gray underneath, and produces the same reddish "blood sweat" secretion as the common hippo — hipposudoric acid, which is believed to have antiseptic and sunscreening properties. Because hippo skin dries and cracks quickly, both species depend heavily on water.

The pygmy hippo's skeleton is more gracile than the common hippo's, with proportionally longer legs and neck and a smaller head. Its back slopes forward rather than running parallel to the ground, likely an adaptation for moving through dense forest vegetation. Its eyes and nostrils are less pronounced than the common hippo's, reflecting less time spent in deep water, and its feet are narrower with less webbing between the toes, suited to walking on the forest floor. Pygmy hippos were unknown outside West Africa until the 19th century; they were introduced to zoos in the early 20th century and breed well in captivity, so most research on the species comes from zoo animals rather than wild studies.

Behavior and diet

The pygmy hippopotamus is reclusive and nocturnal, and much of its behavior resembles that of a tapir more than that of its own larger relative — a case of convergent evolution. While common hippos are gregarious, pygmy hippos live alone or in small groups, typically a mated pair or a mother and calf, and tend to ignore each other rather than fight when they meet. Field studies have found that a male's range covers about 1.85 km2 (460 acres), while a female's covers 0.4 to 0.6 km2 (100–150 acres). They spend most of the day hidden in rivers, often resting in the same spot for several days before moving on, and at least some make use of dens or burrows along river banks.

At dusk, the pygmy hippo emerges from the water to forage, following game trails through dense vegetation and marking them by waving its tail while defecating. It spends about six hours a day feeding. As an herbivore, it rarely eats grass, which is uncommon in the thick forest it inhabits; instead, the bulk of its diet is herbs, ferns, broad-leaved plants, herbaceous shoots, forbs, sedges, and fallen fruit. The wide range of plants it has been observed eating suggests it will take whatever is available, and its diet is considered higher quality than the common hippo's.

Sexual maturity arrives between three and five years of age. The female's oestrus cycle averages 35.5 days, with the fertile period lasting 24 to 48 hours, and pairs may mate one to four times during that window. Gestation runs 190 to 210 days and usually produces a single calf, though twins are known. Unlike the common hippo, which mates and gives birth only in water, pygmy hippos do both on land or in water, and calves can swim almost immediately. Newborns weigh 4.5–6.2 kg (9.9–13.7 lb) and are weaned between six and eight months old; before weaning, a calf hides alone in the water while its mother forages, and she returns about three times a day to nurse it. Although generally docile and not considered dangerous to humans, pygmy hippos can be highly aggressive at times, and several attacks have been recorded — most provoked by human behavior, though a few had no apparent cause — though no human deaths.

Range and habitat

The pygmy hippopotamus is native to the forests and swamps of West Africa, primarily in Liberia, with smaller populations in Sierra Leone, Guinea, and Ivory Coast. It has been extirpated from Nigeria, where a distinct subspecies once ranged in the Niger River Delta near Port Harcourt until at least the 1940s, and possibly from Guinea-Bissau as well.

As a difficult, rare, nocturnal forest animal, the pygmy hippo is hard to study in the wild, which is part of why so much of what is known about it comes from zoo populations rather than field research. It relies on water to keep its skin moist and its body temperature cool, and while it shows more terrestrial adaptation than the common hippo, it remains more aquatic than any other land-dwelling even-toed ungulate — its ears and nostrils have strong muscular valves that let it submerge.

Conservation status

The pygmy hippopotamus is listed as Endangered on the IUCN Red List. The 2015 assessment estimated that fewer than 2,500 pygmy hippos remain in the wild, and the species' survival is considered more assured in captivity than in its native range.

The greatest threat is habitat loss. The forests where pygmy hippos live are being logged, settled, and converted to farmland, with little effort toward sustainable practices. As forests shrink, populations fragment, reducing genetic diversity in the remaining mating pool. Pygmy hippos are also hunted illegally for food in Liberia, where their meat is said to be of good quality, and the effects of regional civil conflict are unlikely to have helped.

In 2007 the EDGE of Existence project named the pygmy hippo one of its top 10 focal species, and some populations live in protected areas such as the Gola Forest Reserve in Sierra Leone.