Trophic Level II - The Herbivores Hippopotamus Page 41

  Hippopotamus amphibius

Length: 280-350 cm (9-11.5’)

Height: 130-165 cm (51-65")

Tail: 35-50 cm (14-20")

Weight: 510-2500 kg (1124-5500 lb.) female, 650-3200 kg (1433-1260 lb.) male

Status: Common, but greatly reduced in numbers from those seen in the past.

Habitat: Hippos require an environment that offers them opportunity to graze at night and permanent water to rest in during the day. Large groups prefer water locations that have firm, gently sloping beaches and quiet waters. They must also have access to the grassland from their daytime resting places. On the Mara River, where the banks can be quite high, they have eroded deep trails up to the top of the banks. These trails are also used by wildebeest and other animals when they cross the river.

Hippos are found in most rivers of the Serengeti-Mara provided the water meets their needs. Their constant moving about in rivers helps prevent the rivers from becoming clogged with vegetation.

Hippos were once found as far north as Egypt but have been systematically eliminated from many areas. Hippos had a reputation for killing more humans than any other African mammal. Most of these deaths were caused when a hippo turned over a fishing boat and the occupants, unable to swim, drowned. Hippos, being large, were often hunted for food and wounded animals would also attack boats. Even today, there are some lakes where the hippopotamus remains aggressive.

Never get between a hippo and its water refuge. They can run over 30 kilometers per hour (18 mph) and will steam roll over anything in its path if it is frightened and seeking safety.

Hippo populations have been greatly reduced in order to eliminate their potential threat. Even so, there are still about 160,000 hippos in Africa today.

Food: Hippos are night time grazers. They are usually alone while feeding but calves will accompany their mothers. When there is a high density of hippos in an area, they will remove most of the taller grasses and "mow" the grass very low. This inhibits grass fires because it deprives the flames of the dead grass they need to keep burning. This may even help riverine forests prosper by preventing fires from reaching them.

Hippos favor the following species of grass: Cynodon, Panicum, Brachiara, Themeda, Chloris and Setaria. They eat both creeping and tussock grass types.

In a night, a hippo will eat between 40 and 60 kilograms (88-132 lb.) of grass. It usually requires about 5 hours of non-stop feeding to harvest this much. While this seems like an enormous amount of food, it is really well below the ratio of food to body weight that other large herbivores require. A hippo needs to consume approximately 1.5 times its own body weight a year. A rhino or elephant must eat about twice theirs. Why the difference in the ratio?

Hippos have very sensitive skin and must protect it from the sun's rays. To do this, they retreat to the water where the mud and water give them a measure of relief. Water helps the hippo keep a constant body temperature and this reduces the amount of food it needs.

There is a myth that hippos sweat blood. This is not true. They do produce a pinkish oily skin secretion that helps protect them from the sun's rays.

Ecologists sometimes speak of the hippo as an "energy sink". By this, they mean that its dining habits return very little of the nutrients it consumes to the soil that produced them. Hippo feed on the grasslands that surround their habitat. Very little of the processed food (in the form of dung or corpses) is ever left on the land. This, the ecologists say, deprives grass and soil of needed nutrients. In effect, the nutrients are not re-cycled the way a wildebeest re-cycles the nutrients it consumes while feeding. (Wildebeest deposit their dung on the ground and they usually die on land.)

Most of the nutrients a hippo consumes are released into its watery environment. Hippos spend most of their day in the water where they dung frequently, whipping their droppings away with their short stubby tails. This enriches the water's content and provides food for fish that feed on the unprocessed bits of grass in the dung. Crocodiles, other fish and birds all feed on these fish. Hippos usually die in the water too, further enriching it.

Social System: Hippos have a hierarchical society. Each individual knows its place in the pecking order and must acknowledge the presence of a superior. They do this by lying down and by frequently urinating and defecating.

Females, accompanied by up to four of their offspring are the only stable unit. Some individuals will move from location to location while others will be associated with one area for long periods of time. Hippo society is highly variable.

Large adult bulls will defend a territory and breeding rights for some time. They will tolerate subordinate bulls as long as they show no inclination to breed with the territory’s females.

Hippos are generally belligerent animals. Constant yawning is often a threat gesture that displays their teeth. Fights are common and serious fights between rival bulls can turn deadly. Razor sharp, 60 centimeter (24") long teeth can carve up an enemy quickly.

Hippo herds, whether male or female, are quite changeable both in members and in numbers. A herd may consist of between 2 and 150 individuals. Bulls will try to keep cows in their stretch of water.

Herds themselves keep in contact by snorting and bellowing in unison. Herds up the river will then return the calls. Herds are typically at least 100 meters (328 feet) apart in suitable territory.

Behavior: Other then feeding, almost all other hippo behavior occurs in the water. They court and mate there. They fight there. Females give birth to a single calf either on land or in the water. Sleeping hippos rise automatically to breathe. Hippos can stay under water for up to five minutes.

A cow leaves the herd and seeks an isolated place to give birth. Calves are born after an eight month gestation period and weigh between 48 and 121 kilograms (106-267 lb.) at birth. Mother and calf will stay apart from the herd for at least 10 days as long as 44 days. Calves stay close to mom for protection against crocodiles and other predators. If they join the herd too soon however, they face the danger of being trampled by other herd members when they make a dash for the water. Young hippos are excellent swimmers and can even suckle under water.

The constant tail wagging of hippos spreads their droppings and marks their space. Scientists have only recently begun to unlock the secrets of hippo communication. They are one of the most vocal of all the mammals. They use a variety of grunts, snorts and bellows to advertise their presence. One bellow was recorded at a level of 115 decibels. That is the equivalent of having a heavy metal rock band playing 5 meters (16 feet) away.

Sounds of Hippos

Hippo sounds have been well known. Recently, however, scientists have lowered underwater microphones into the hippos’ watery domain. There, they recorded an unknown world of hippo vocalization. Water is 800 times denser than air and carries sounds much better than the thinner, less dense air. However, sounds produced in air do not carry underwater. The sounds that hippos make when they come to the surface would go unheard by hippos underwater.

Hippos do hear sounds underwater not so much by using their ears as with their jaws. Hippo jaws, like those of whales, pick up the vibrations of infrasonic (very low) sound waves produced by another hippo. It is now believed that fat channels or some other as yet unknown mechanism carries the sound to the hippo's brain. Hippos lack the scope of a whale's singing ability but do produce a number of infrasonic noises that seem to convey messages. Low frequency sounds travel further underwater than high frequency (ultrasonic) sounds do. Their sounds have been described as "soft flutters", "plaintive moans", "staccato clicks" and "squeals". Almost 80% of hippo vocalization happens underwater.

Male hippos are bigger than females and have more developed jaw muscles and teeth. They do not defend breeding territories until they are twenty years old. River territories are between 50 and 100 meters (164-328 feet) long. Territories on lakes are almost twice that size and can be up to 500 meters (1,102 feet) in length. Males may hold a territory for a long time. Eight years is not unheard of and four years seems to be a fairly common time to maintain a territory.

A group of mother hippos will mob a bull if he creates too much of a fuss in the herd and endangers the calves.

Predators: Lion and spotted hyena will both take hippos on land. Crocodiles are a threat in the water. There seems to be an uneasy truce between hippos and crocodiles. For the most part, the two species ignore each other. It is rare for a crocodile to attack a young hippo. Hippo mothers are very defensive and will attack the reptile.

Hippo Population Estimates 1990

(Author’s note: In the past, hippos probably killed more people in Africa than any other mammal, except humans. They have been known to turn over fishing boats causing the hapless boaters to drown. Never get between a hippo and its safety refuge, water! They will run over you in their attempt to get to safety.)

Select a Page:
1    2    3    4    5    6    7    8    9    10  11  12  13  14  15  16  17  18  19  20  21  22 
23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42 

CDROM Index | Title Page | Contents | Index | Glossary | Bibliography | Appendices | LifeStories Online

Dave Taylor's African Safari - Book 3: Trophic Level II - The Herbivores (Standard Version)
Copyright © 1999 Dave Taylor & James Cash