Hippopotamus (Hippopotamus amphibius)
Weighing between 1,300 and 3,200 kg, Hippopotamus (Hippopotamus amphibius) inhabits the lower reaches of rivers and spends the day in water emerging at night to feed on short grass swards. They seldom move more than 3 km from water and visit previously-grazed floodplain sites where their feeding activities maintain ‘hippo lawns’.
Hippos have stumpy legs, splayed toes and no protective hooves reflecting the amount of time spent in water where their movement is facilitated by long supple back and kicking movements of the hind limbs. Water is used as a daytime refuge, and the ears and nostrils have muscular valves allowing submergence.
Hippos have a marked preference for deep backwaters rather than for fast-flowing reaches. They are gregarious during the day, and form unstable groups of females and bachelors; mating takes place in water, and males fight fiercely over access to females. The massive aquatic mammals have thick skin devoid of sweat glands, and thus they depend on water to cool their bodies. They appear physiologically adapted to minimise energy expenditure and accumulate large amounts of fat.
This large, lumbering aquatic animal occurs naturally on most African lakes and waterways, where it spends most of the day submerged, but emerges from the water to graze at night. Hippos are strongly territorial, with herds of ten or more animals being presided over by a dominant male.
In Uganda, the best places to see the hippopotamus are in Murchison Falls, Queen Elizabeth and Lake Mburo national parks, where they are abundant in suitable habitats. Hippos are still quite common outside of reserves, and they are responsible for killing more people than any other African mammal.
Hippopotamus essentially translates to the Greek for “river horse“.
Bulky and barrel-shaped, it would seem hippos would be clumsy on both land and water. However, adaptations to their semi-aquatic environments have allowed them to move swiftly on both water and land.
On land, they are able to move at speeds up to 30 km per hour and can maintain these speeds for several hundred meters. In shallow waters their short legs provide powerful propulsion through water, while their webbed feet allow them to navigate on shallow river bottoms.
Placement of eyes, ears, and nostrils high on their head allows them to remain mostly submerged while still being able to breathe and stay aware of their surroundings. When completely submerging, the nostrils close and ears fold to prevent water from entering them.
The jaws of hippopotamus are capable of opening up to 150 degrees, showing enormous, sharp, incisors and canine tusks. Canines grow to 50 cm and incisors grow to 40 cm, sharpening themselves as they grind their mouths together during grazing.
Hippopotami are a very social species, living in groups of about 20 to 100 individuals. They lead very sedentary lives, resting most of the day and leaving their resting pools at dusk to feed. Most of their activity is nocturnal.
Females are the leaders of the herd, controlling the centers of the resting pools. Males rest along the outer banks of the pools, protecting the females and calves. By age 7, males compete for dominance. Dominance is usually displayed with yawning, roaring, dung showering, and jaw clashing. Dominant males are usually very intolerant of juveniles attempting to challenge them. Larger males have a tendency to harm or kill the young males during these displays.
Territorial behavior consists of wheezing, honking, and dung showering. When approaching new territory they stop and turn their backside towards the area, lift their rear in the air and release dung and urine. Their tails swing back and forth scattering the excreta around the unfamiliar boundary. Male hippos often emerge from the water to spread dung along the shoreline and their grazing paths.
Juvenile hippos can often be found following dominant males around smelling and licking their rears. Fighting and defensive displays are usually most intense during the dry season, when living conditions are more crowded and resources are scarce. Defensive displays such as yawning, jaw and tusk clashing, biting, and retreating to resting ponds are common in fighting between males as well as protection of the herd against predators.
Hippopotamus leaves their resting waters at dusk, moving down familiar paths, “hippo paths“, to grassy areas surrounding their waterbeds.
Hippos prefer to remain close to water beds, however they will travel,between four and five hours each night, in circular patterns for several kilometers covering between 3 and 4 km when food is scarce.
Their mainly frivolous diet consists of small shoots, grasses, and reeds. They do not dig for roots or fruits. However, they will consume many other types of plants if they are present. Muscular lips, 50 cm wide, are ideal to pull up grasses.
Hippos do not use their teeth to chew their meals, and instead they tear and soften the grasses to prevent any nutritive loss. While their sedentary lifestyle allows for a simple diet, they are known to consume an enormous amount of food each night, 1-1.5% of their body weight (usually around 40 kg of food).
Hippopotamus enter and exit their water pools at the same spot, returning from grazing before dawn. Occasionally, if the hippo has traveled too far it will seek a nearby pool to rest in until the following nightfall.
Hippopotami are monogastric, non-ruminant herbivores. There is no evidence to show that hippo actually feed on carcass matter although they may sniff at a carcass, pick it up and let it fall again, near their resting pools. Their diet consists 90% of palatable, sweet grasses and 10% reeds and dicot herbs.