Chimpanzees
 
Physical Characters and Distribution
Chimpanzee, ape of equatorial Africa that, physically and genetically, is the animal most closely related to humans. Two species of chimpanzee, or chimp, exist: the common chimpanzee and the bonobo, also known as the pygmy chimpanzee. The common chimp is found in dense jungle and more open wooded savanna from Sierra Leone and Guinea on the Atlantic Ocean to the lakes Tanganyika and Victoria in east central Africa. The bonobo is found only in a small region of thick jungle in the Democratic Republic of the Congo (DRC, formerly Zaire) in central Africa. Both species of chimpanzee are listed as endangered species.
The male common chimp is up to 1.7 m (up to 5.6 ft) high when standing, and weighs as much as 70 kg (154 lb); the female is somewhat smaller. The common chimp’s long arms, when extended, have a span half again as long as the body’s height. The bonobo is a little shorter and thinner than the common chimpanzee but has longer limbs. Chimpanzee feet are better suited for walking than are those of the orangutan because the chimp’s soles are broader and the toes shorter. The coat is dark; the face, fingers, palms of the hands, and soles of the feet are hairless; and the chimp has no tail. A bony shelf over the eyes gives the forehead a receding appearance, and the nose is flat. Although the jaws protrude, the lips are thrust out only when a chimp pouts. The brain of a chimpanzee is about half the size of the human brain.
The chimpanzee is diurnal and omnivorous, eating about 200 kinds of leaves and fruit; termites, ants, honey, and birds’ eggs; and birds and small mammals. It lives in or near trees, avoiding direct sunlight. An adult builds a sleeping nest each night in a tree. The female has a 35-day menstrual cycle, is receptive to mating for 6.5 days out of each cycle, and can breed at any time of the year. The female may mate with different partners. The gestation period is more than seven months long, and a single offspring or rarely, twins, is produced. Immediately after birth the helpless young clutches its mother's hair, riding on the mother’s back when she travels. Common chimps are weaned at about four years, and bonobos are weaned at about five years. In both species, the young may continue to travel with the mother until the age of ten. Offspring sometimes maintain a bond with the mother throughout life. Chimps in the wild live about 40 years and many in captivity live over 50 years.
Scientific classification: Chimpanzees belong to the family Pongidae in the order Primates. They make up the genus Pan. The common chimpanzee is classified as Pan troglodytes. The bonobo is classified as Pan paniscus.
Just one hundred years ago, chimpanzees populations in Africa were estimated to be in the hundreds of thousands. Currently, however, estimates describe approximately 180,000 chimpanzees living within equatorial Africa. At one time, twenty five African nations hosted chimpanzee troops. As of 1990, communities had disappeared from four of these countries and were depleted in seven others to the extent that regional extinction was imminent. The map below illustrates current chimpanzee distribution in Africa. Notice that chimpanzees predominantly inhabit regions of forest just south of the equator. When comparing distribution with the vegetation map, the correlation becomes obvious. Chimpanzee range is restricted to the regions within Africa dominated by tropical vegetation. Chimpanzees rely on the tropical forests of Africa for both food and shelter and are well adapted for a sylvan lifestyle as will be further discussed.
Social behavior
Chimpanzees form loosely organized bands of 2 to 80 individuals on fairly large home ranges, where the animals remain for years. Within a community, smaller groups may form, break up, and reform; sometimes a female migrates to another community. Males never migrate. Except between mother and young, little permanency exists in individual relationships. Members of a community cooperate in hunting and sharing food. On finding a food source, they hoot, scream, and slap logs to attract others. A constant interplay occurs between adults, and all members of the group groom one another.
Chimpanzees communicate through vocalizations, facial expressions, posture, touch, and movement. Studies show that a young chimp is able to make as many as 34 different calls, and the facial musculature can express a wide range of emotions. The animals show great intelligence in problem solving and the use of simple tools, such as a stripped twig used to draw termites from their nests. A number of experiments have shown that chimps can even learn to use sign language or other languages based on pictures or symbols. However, critics maintain that this does not constitute an understanding or use of words.
The greatest threats to chimpanzees are the continued loss of habitat to logging and agricultural development, and the hunting of chimps for export to zoos, for scientific research, and food. Conservation efforts that prohibit the hunting and sale of chimpanzees provide some protection; however, these bans are difficult to enforce. Sanctuaries for orphaned and recaptured animals provide the common chimp with additional protection in Zambia and Gambia, as does Salonga National Park for bonobos in the Democratic Republic of the Congo.
Range and habitat
The gorilla, the common chimpanzee, and the bonobo live in dense tropical forests on the African continent. Chimpanzees also inhabit wooded savanna, where there are more opportunities for foraging out in the open. Most gorillas live in the hot, lowland forests of west and central Africa, but a subspecies called the mountain gorilla lives in a very different habitat. Its range extends as high as 3400 m (11,200 ft) on the cool, mist-covered slopes of the Virunga Mountains.
The gibbons and orangutans inhabit Southeast Asia. Gibbons live in rain forests and seasonal forests of India, Indochina, and the Malay Archipelago. The orangutan is purely a rain forest animal. Today its range is restricted to two large islands—Sumatra and Borneo—but fossils show that it once had a far greater range, reaching as far north as China.
Food
Chimpanzees are omnivores, for they eat a combination of meat and plant material. Much of a chimpanzee’s day is spent eating or finding food. It is estimated that during a typical chimpanzee day, 47% of its waking hours are spent eating, while 13% are spent traveling between food sources. Although feeding occurs all day, consumption peaks occur around daybreak until about 9:00am and also from late afternoon to sundown .
Despite the incredible amount of time spent eating and foraging for food, chimpanzee feeding is not random. Rather, specific feeding locations are visited according to seasonal availability and preference. Although the overall abundance of food is greatest during the wet season, as would be expected, the dry season does not usually deplete food supplies to such an extent as to result in starvation. As an adaptation to the seasonal availability of food, chimpanzees entertain a diet that responds accordingly.
The time spent at any one feeding site seems to be proportional to the amount of time necessary to prepare and eat the food. Chimpanzees are very selective in the quality of the food that they eat. Many will poke and massage food in order to test ripeness before eating. Additionally, certain foods are associated with unique consumption rituals. For instance, the leaves from Ficus urceolaris, a species of fig, are individually picked and folded over before being chewed, whereas the leaves from Aspilia sp. are pressed against the palate in the mouth and in fact never chewed. Many of the seeds eaten by chimpanzees are encased in hard shells and must be broken before the individual is able to access the seed . Therefore, certain feeding sites require greater food preparation than others and are thus associated with visitations of longer duration by feeding chimpanzees.
Long-term observation studies have noted an incredible variety in chimpanzee diet. It is clear that this variety results from the desire for alternative foods, rather than the lack of a food supply large enough to satiate an individual, for a chimpanzee will almost always leave a food supply before its total depletion in search of a different food source . Vegetative mass comprises the bulk of chimpanzee diet. Scientists have recorded 158 plant varieties eaten regularly by chimpanzees. According to meticulous observations, the average chimpanzee diet is composed of 25% leaves and leaf buds, 27% of other plant mass such as pith, seeds, blossoms, bark, and stems, and supplemented by the consumption of small prey. Within the category of small prey fall the prized red colobus monkey, bush pig, and birds eggs, as well as the dietary staple of insects. Chimpanzees have also been noted to eat small amounts of soil, which is hypothesized to provide necessary minerals and vitamins, such as halite and sodium chloride.
Scientists have observed two important trends related to chimpanzee consumption of insects. One is tool-making and tool-use. In order to acquire enough tiny ants or termites to satiate a chimpanzee, an effective method of obtaining large numbers of prey is necessary. Clearly, eating ants individually would expend a costly amount of time and energy. Instead, chimpanzees have been observed to strip the leaves off of young sapling branches and poke them into the borrows of ant or termite nests. Infuriated, the insects rush out of their homes via the sapling which is then drug across the lips of the chimpanzee, dumping hundreds of insects into its hungry mouth . The second observation of importance is that females tend to consume larger amounts of insects than males. Researchers hypothesize this to be a result of different dietary needs between male and female chimpanzees.
Differences in male and female diets have been noted in relation to meat eating as well. Small packs of chimpanzees, almost always entirely male, occasionally work together in order to hunt small monkeys or other bush meat. Often, an individual will move towards the prey, encouraging it to flee in the direction of a nearby tree in which the remaining members of the hunting pack anxiously wait. If numbers permit, a chimpanzee may also wait below his comrades on the ground, in order to prevent escape. Since it is mostly males that participate in this hunting ritual, it is also mostly males that benefit from it. A captured monkey is a highly prized possession, one hoarded away from other community members. The only way for a female to acquire meat is through begging. Although this does not provide a great amount of food, a mere taste at most, most males will share a small portion of their prize with the outstretched fingers that surround him .
Water
Most of a chimpanzee’s water supply is acquired through food, namely juicy fruits and the moist leaves of plants. During the wet season, when fresh streams run through a community’s territory and rain is frequent, a chimpanzee may drink up to three times a day by either sucking water from a stream or using spongy leaves to soak up water from small pools within roots or tree trunks .
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