The Sunday News
Know Your Wildlife
Ndebele — Imvubu, Shona — Mvuu
THE hippopotamus is a large mostly herbivorous mammal in sub-Saharan Africa.
It is one of the two species in the family Hippopotamidae that are still alive, the other is the pygmy hippo. The hippopotamus is the third largest land mammal after the elephant and the white rhino. It is also the heaviest artiodactyls weighing about 1 500 kilogrammes. Although it has short legs it can easily outrun a human, running as fast as 30 kilometres per hour for short distances. It is one of the most aggressive and unpredictable creatures in the world and as such ranks among the most dangerous animals in Africa.
Description
Hippopotamuses are characterised by their great size. They have short barrel shaped bodies and short stout legs. Unlike most semi-aquatic animals, the hippopotamus has very little hair. Their mouths are wide and very large and the jaws are armed with tusk like incisor and canine teeth. Both the incisor and canine are unusual in that they grow continuously. The eyes, nose, and ears are positioned in a way that they protrude from the water when the Hippo is submerged. This is an adaptation for their semi- aquatic life.
Distribution/Habitat
Hippos require sufficient open water in which they can submerge themselves. They may be found in swampy areas, lakes, rivers and streams. They prefer shallow standing water near sandy banks on which they can bask in the sun. They use these pools over a period of many years provided food supplies remain available to them. Seasonal flooding may cause them to move temporarily from their established resting pools.
Habits
Among the ungulates only hippos are truly amphibious. They feed nocturnally on dry land and spend much of the daytime in water where mating and calving take place. Adult hippopotamuses can remain underwater for five to six minutes. Hippos live in schools which may number up to 15 individuals. The schools consist of the territorial male, adult females and juveniles of both sexes. The schools break up in the evening when the hippos depart to graze. While hippos rest near each other in the water, grazing is a solitary activity. They do not spend the whole night feeding and may rest lying down under bushes or even return to water. On dry land they tend to use established routes, the ground eventually becoming bare. The paths have a central ridge where the grass is still intact.
Bulls are territorial and they maintain these territories for long periods of time. The bulls establish territories in water and they are not territorial on land. Territorial bulls may be challenged and this is dependent on density and also climatic changes affecting territory size.
Territories are advertised through dominant behaviour and ritualised defecation combined with urination. Defecation in the same place and flapping their tails from one side to another result in the accumulation of dung piles measuring several square metres. Dung piles do not function as markers and are not produced only by the territorial bull but by all males passing the site. Dung piles are also found where the hippopotamus graze, outside the territories, as well as along footpaths. Moreover, hippos wag their tails when defecating thus scattering the dung over a wide area.
The habit arose in water where smaller pieces of dung would drift away in the current rather than sink as a big mass and accumulate on the river bed. Serious fights occur among territorial bulls and they can result in serious injury leading to death. Relationships between territorial bulls and other bulls are very friendly provided the latter are subordinate. Apart from the territorial bull, recognisable by the larger size of his head and neck, few dominance relationships seem to exist in hippopotamus groups. The only stable associations are those of a cow and her young until they are fully grown at six to eight years.
Food
Hippopotamuses are selective nocturnal grazers, consuming about 40 kilogrammes of grass per night. The grass is plucked with an upward movement of the head. Grass is digested and fermented in the stomach with the aid of micro organisms. They prefer to feed on open areas of short green grass. Hippos are notorious crop raiders and can become a problem where crops are grown near rivers in which hippos live.
Reproduction
Hippos are polygynous, that is, one bull mates with several females in the pond. Hippos mate in water, where the female remain submerged except for brief intervals to breath. The gestation period is about eight months. Females have their first calves at about four years old and males reach puberty when they are about seven years old. When they are about to calve the female leaves the group and finds a secluded site in shallow water to give birth to the single young which weighs about 50 kilogrammes. The calves rest on their mother’s backs when the water is too deep for them and they swim under water to suckle. Weaning starts between six and eight months after birth and most calves are fully weaned after a year. Calves are prone to predation by crocodiles but adult hippos are extremely hostile towards crocodiles and are very dangerous when in the presence of humans. On land calves fall prey to lions and hyaenas, against which the female will put up a spirited and often successful defence.