Hippopotamus

Hippopotamus amphibius (Linnaeus, 1758)

Photo: Marius Saunders

IUCN Conservation Status:

River hippopotamus = Lower Risk, least concern (LR/lc). The extant global population is estimated as being between 125 000-150 000.
Pygmy hippopotamus = Critically Endangered (CR)

Hippo are the most unpredictable and moody of all African animals. Zee-paarden, the Dutch for “horse of the water” was the first citation on the wildlife of the Cape in Jan van Riebeeck’s journal in 1652. Van Riebeeck associated the animal with the sea, as hippo was abundant in nearby marshy lagoons, especially those of Muizenberg and Zeekoeivlei. There were also large numbers to be seen in the Berg River. Several other names followed; “zeekoe”, sea-horse, sea-cow and, in the 1700’s, those in the Nile River were called “Nylperd” or Nile-horse. Eventually the name hippopotamus or hippo was given to the animal. The name hippopotamus is derived from the Greek for horse “hippo” and from river “potamus”. The “Behemoth” animal referred to in the Bible was an extinct hippo species.

Taxonomy 

Classification

The oldest known true hippopotamid is the genus Kenyapotamus found in Africa 20-8 million years BP. Fossils dating back 20 million years BP were found in Kenya. Hippopotamidae are believed to have evolved in Africa and then spread across Europe, through Asia to Indonesia. They did not cross into the Americas. From 7.5–1.8 million years BP Archaeopotamus, an ancestor of the modern hippopotamus Hippopotamus and Hexaprotodon (also referred to as Choeropsis), lived in Africa and the Middle East. Scientists disagree as to whether the modern pygmy hippopotamus is a member of Hexaprotodon the Asian hippos from the Pliocene, or of Choeropsis from the older Pleistocene. As many as three species of the dwarf Malagasy hippo became extinct on Madagascar during the Holocene. Two species ranged in Europe and the British Isles Hippopotamus antiquus and H. gorgops, but were extinct before the last Ice age. Only three species survived of which two are found in Africa, the first being the hippopotamus or river hippo. 

Hippopotamus amphibius with five subspecies:

• H. a. amphibius found in the Nile River from Sudan to the north of Tanzania, and down the Rift Valley to Mozambique. It was recently eradicated in Egypt. Book a holiday to Sharm el Sheikh
• H. a. kiboko found in the Horn of Africa, Kenya and Somalia
• H. a. capensis distributed from Zambia to South Africa
• H. a. tschadensis found throughout western Africa to Chad
• H. a. constrictus of Angola, the southern Democratic Republic of Congo and Namibia, The second species is the pygmy hippopotamus Hexaprotodon liberiensis, formerly Choeropsis liberiensis with two subspecies
• H.l. liberiensis the Liberian pygmy hippopotamus
• H.l. nigeriensis the Nigerian pygmy hippopotamus

The last surviving species is the Madagascan pygmy hippopotamus Hexaprotodon madagascariensis.

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Description

A large amphibious mega-herbivore, with a large, barrel shaped body and short, stout legs like an enormous pig. The head is broad and well developed and supports a massive mouth with jaws that open up to 50 cm wide. The river hippopotamus has four incisors and the pygmy hippopotamus six. Other extinct hippos had only two incisors. Other than some sparse, brush-like hair on the chest, lips, neck, ears and the tail end, the skin is virtually naked, smooth and moist, a dark greyish-brown with a pink tinge. It appears pinker when the hippo is out of the water due to a red, slimy, viscous fluid secreted by glands in the inner skin layer, giving rise to the myth that hippos sweat blood. The nostrils contract and close when a hippo is submerged for up to 6 minutes. Hippo can charge at speeds of up to 35 km/hr on land, and in water they cannot swim but walk or gallop on the bottom at speeds of up to 22 km/hr. Adult bulls are much larger than cows, weighing up to 2 500 kg. After the elephant the hippo and white rhino is currently the second largest living terrestrial animals. A body mass of 770-950 kg is reached at 7-8 years, of 1 400 kg at 11 years and >2 000 kg after 20 years age.

The pygmy or dwarf hippopotamus is much smaller with a mean adult body mass of 160-190 kg for cows and 200-280 kg for bulls and a mean shoulder height of 82 cm. The snout is smaller and narrower than the river hippo and the hide is bluish-black, sometimes with a dark green tinge.

Comparison To Man

Trophy

Hippopos do not possess horns but have ivory tusks similar to those of the elephant and warthog. The canines of both jaws and the incisors of the lower jaw grow continuously. They are popular in the ivory trade as, unlike elephant ivory, hippo ivory does not change colour with age. The lower incisors grow forward horizontally while the lower canines grow vertically upwards in a half circle. The upper canines grow vertically downwards and are rudimentary compared to the lower canines. The largest trophy is not necessarily found in the oldest hippo as tusks are inclined to wear after reaching 20 years.

Habitat requirement

Permanent river systems or water rich environments such as dams or wetlands. These must have deep pools with gradually sloping bottoms, dry sandbanks and at least a 5 km radius supply of suitable grazing. It can be found from the rivers of the equatorial tropics to desert environments such as the Nile River in the Sahara, the Orange River in the Richtersveld and the Fish River in the Namib. Hippos rapidly change the structure of tall grass stands to their preferred short grass grazing. Hippos readily move up and down watercourses between temporary pools. They climb the steep slopes of mountains and ridges to an altitude of 2 400 m in search for food and suitable habitat and may remain there for many years if left undisturbed. In contrast, the pygmy hippopotamus prefers forest-like habitats.

Distribution

Feeding & Nutrition

The activities are restricted mostly to the night hours between 20:00-4:00 and 7-8 hours of feeding per day. They move distances of up to 30 km with a mean of 5-8 km per night on land. Hippo roam an average distance of 3-5 km from water to a maximum of 10 km. Most daylight hours are spent lying either in the water or on dry sandbanks. Adult bulls sometimes sleep under thick bushes on land. Hippopotami are monogastric, non-ruminant herbivores. The diet consists 90% of palatable, short sweet grasses and 10% reeds and dicot herbs. A partly selective roughage feeder consuming plant matter with high crude-fibre content, but rich in carbohydrates and protein. Short grasses less than 12 cm is preferred, although taller grass may be consumed until the habitat has been transformed into a lawn-like stand. A mean of 40 kg fresh grass material, approximately 10% of its body mass, is consumed per adult hippo per night. In captivity they can be maintained on 1-1.5% of their body mass per day. When environmental conditions deteriorate and food and water are not available, they often survive in muddy wallows for weeks by lowering their metabolic rates and relying on the stored body fats in the skin. The large 3 m long stomach has four chambers divided into two blind sacs by a septum, contributing to a slower digestive process than that of ruminants. This slow rate, enhanced by calm resting after rapid feeding on land at night, results in an improved digestion and absorption of ingested dietary nutrients. The hippo lacks the caecum found in hindgut digesters such as the elephant.

Social structure

Hippo are semi-gregarious living in small family groups in the water during daylight hours. At night the groups split up and roam and graze as individuals or couples that are mainly mothers and calves.

The social structure are:

• family groups of 5-30 individuals, including 2 bulls >20 years (one is dominant), 5-10 cows >11 years, several sub-adult females 4-8 years, 4-8 sub-adult males 4-10 years and calves <4 years. The sub-dominant bull and the sub-adult males avoid conflict with the dominant bull by keeping to the perimeter of the family. They are not tolerated by the cows. At the first sign of a challenge to its leadership the dominant bull immediately attacks aggressively
• bachelor herds of 4-8 individuals, of young bulls >10 years, not associated with family groups, that inhabit their own water pool
• post mature solitary nomad bulls occupying smaller bodies of water.

Photo: Doug Lee

Territorial behaviour of dominant bulls, associated with a family herd, is restricted to the water and immediate shoreline. Social or hierarchical behaviour does not exist inland. Hippopotami are non-static and move regularly in search of alternative habitats during annual environmental changes. Nightly movements of up to 30 km can occur between dams. When water sources are depleted, families form temporary mass herds of up to 150 individuals and share the remaining pools. During this time the social order is disrupted, creating enormous confusion among the bulls that attack and kill the young. These aggregations break up when the last of the water has evaporated and individuals become single nomads that often die if alternative resources are not quickly found. Single groups consisting of one adult bull and 1-3 family members are often kept in small remote dams on ranches. This is a recipe for disaster as there is no alternative habitat or space to support the social structure of the additional male offspring in the system. This can result in fights to the death or to the escape of hippo bulls into neighbouring grounds.

Information Table

Bibliography