Wild Hippos

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Biological Classification

General Description

As hippo expert Hans Klingel once noted, "Few animals are as recognizable as the hippopotamus." Indeed, it is almost impossible to mistake a hippopotamus for anything else. The body is long, barrel-shaped, and very deep. [I always thought they were more potato-shaped.] The limbs are short and pillar-like, with four toes on each foot. The hippo's neck is short and quite thick in order to support the weight of the massive head. The ears are small and round, the eyes are bulbous and protruding, and the muzzle is broad and rounded. The hippo's mouth is especially large; in fact, the hippo can open its mouth wider than any other living animal except the whales. The upper and lower canine teeth--often referred to as tusks--are long, thick, and very sharp. The animal has no hair except for a few stiff bristles on its muzzle, ears, and stubby tail. The skin color ranges from slate gray to copper brown on the back to pinkish purple on the belly and around the ears and eyes.

There is no doubt that the common hippopotamus is one of the world's largest land mammals, but exactly how large appears to be a matter of debate, even among the experts. For example, Encyclopædia Britannica lists the hippo's mature weight as a hefty 3.3 to 5 tons, The Encyclopedia of Animals: Mammals reports it as a respectable 5300 pounds, and Zoo Animals: A Smithsonian Guide states that it is a mere 2500 pounds. According to the London Zoo, the highest recorded weight for a mature hippo is 8,920 pounds. Depending on which source you consult, an adult hippo can stand anywhere from four to five and a half feet tall at the shoulder and be from eleven to fifteen feet long. Understandably, there is some disagreement as to whether the hippopotamus is the second- or third-largest living land mammal. For more on this matter, see The Hippo/Rhino Question.

Special Adaptations

Technically, the hippopotamus is a terrestrial, or land-dwelling, mammal. Because it spends so much of its life in the water, however, it has evolved many adaptations to an aquatic environment. The thick layer of blubber beneath its skin, for example, helps the hippo conserve body heat that would otherwise be lost underwater and also makes the animal more buoyant. The hippo's ears, eyes, and nostrils are placed in a line along the top of its head; this arrangement allows the animal to breathe and to see and hear things above the water while almost entirely submerged. (This head plan can be seen in other amphibious creatures, such as frogs and crocodiles.) The feet are webbed between the toes to help the animal move through the water, and the nostrils can be shut tight when it submerges.

The hippo's present-day range is confined to sub-Saharan Africa. In ancient times, the hippo could be found as far north as the Nile delta. (Indeed, images of the hippopotamus are fairly common in ancient Egyptian art.) Today it is most commonly found in the lakes, rivers, and swamps of East and Central Africa.

Daily Activities

Feeding

Hippos are strictly herbivorous. Each night the herd comes ashore and travels up to five miles inland to graze on short grasses. The paths to the feeding grounds become well-worn with use, and the animals mark the paths with their dung and urine to help them find their way home just before dawn. An adult hippo will consume about 100 pounds of grass each night, which is actually a fairly modest amount for such a large creature. Hippos cut the grass off not with their teeth, like most grazers, but with their broad, tough lips. Where human settlements border the hippos' territory, the hippos will often wander out of their usual grazing grounds and raid the nearby farmlands, where they do much damage.

Structure of the Herd

A hippo herd usually contains ten to fifteen animals, although herds as large as 150 have been observed. A herd typically consists of a dominant male, a few subordinate males, and several females and their young. Young males often form separate but loosely-defined "bachelor" groups along the outskirts of the main herd, and solitary males are not unheard of.

Only the dominant male has the right to mate with the females. Subordinate males are tolerated provided they behave in a suitably submissive manner. From time to time a subordinate male will challenge the dominant male for control of the herd and the right to mate. Such challenges usually lead to violent physical confrontations. (For an exciting description of such a confrontation, see the excerpt from Gerald Durrell's book Encounters With Animals.) The dominant male also establishes the boundaries of his herd's territory along the shores of the lake or river in which it dwells. These boundaries are marked by huge dung piles, deposited by the dominant male, which serve as markers to hippos from outside herds. Territorial disputes are resolved by an odd ritual in which the intruder and the defender first face each other, then present their rear ends and scatter their dung at each other with their tails. Usually, the intruder then retreats.

Temperament

Courtship and Mating

Hippos have a courting ritual of sorts, but it is nowhere near as eleborate as those of most other mammals. As noted above, the vast majority of the mating is performed by the herd's dominant male. Mating most often occurs during the dry season, when the herds are densely crowded together. The ritual begins when the male senses that one of the females in his harem is receptive. The male and female circle each other underwater, occasionally stopping and changing directions, in a sort of slow-motion ballet. From time to time each animal will gently clack its tusks against the other's. (Scientists who studied the hippo's vocalizations using underwater microphones puzzled for years over the source of these clacking noises. The mystery wasn't solved until zoos began building special enclosures which allowed clear underwater viewing of the animals.) After a few minutes of circling, the animals copulate, partly submerged, with the male mounting the female from the rear. Once the act is complete, the female returns to the rest of the herd, and the male resumes his guard duties. There is no further contact between the two.

Still from video taken at Toledo Zoo

Giving Birth

Raising the Young