Physical Characteristics of Chimpanzees
Although wild chimpanzees are only found in Africa, most people are aware of what they look like from zoos, photos and films.
Chimpanzees have black hair and pinkish to black bare skin on their faces (except for hairs on the chin), ears, palms of their hands, and soles of their feet. Infants have very pale skin in these areas and a white tail tuft, which disappears by early adulthood.
Chimpanzees walk on all fours, or "quadrupedally," on the ground and in the trees. As they use their knuckles for support they are sometimes referred to as "knuckle-walkers." This form of locomotion means chimpanzees have evolved to have longer arms than legs. They use these long arms to reach out for fruits growing on thin branches that would not usually support their weight and "brachiate" (swing from branch to branch by their arms).
Chimps have opposable thumbs (although these are much shorter than human thumbs) and their opposable big toes enable a precision grip. Male Chimpanzees are slightly larger and heavier than females. At Gombe in East Africa, adult males weigh between 90 and 115 pounds and measure approximately 4 feet when standing upright. Females are slightly smaller. In contrast, Chimpanzees in West Africa, and in captivity, can be larger. In the wild, Chimpanzees rarely live longer than 50 years, although captive individuals can live for over 60 years.
When Dr. Goodall started her study of chimpanzees in 1960, very little was known about their behaviour in the wild. Since then, studies analysing almost every aspect of chimpanzees’ multifaceted behaviour have sprung up across Africa. In the years since Dr. Goodall began, scientists have reaped a bounty of data from chimpanzee study sites, yielding new insights not only into chimpanzee culture, but into our own culture as well.
Chimpanzees culture is much like human culture: groups in different areas share different cultures. Tool-making is a good example of this variation. Chimpanzees in Gombe use long twigs and alter them for better termite fishing while chimpanzees of the Tai Forest in Cote d'Ivoire are more often seen nut-cracking with rocks and planed surfaces. Even chimpanzees living in separated areas in the same countries will exhibit different cultures and behaviours.
But what kind of behaviors do most sub-species and groups of chimpanzees share? General behaviours like group structuring, communication, and hunting practices are often common from chimpanzee group to chimpanzee group, and even these factors are never constant!
Posture & Gestures
Posture, gesture, and facial expression communicate many messages and emotions within a Chimpanzee community. When greeting a dominant individual after an absence or in response to an aggressive gesture, nervous subordinates may approach with submissive signals - crouching, presenting the rump, holding the hand out - accompanied by pant-grunts or squeaks. In response, the dominant individual is likely to make gestures of reassurance, such as touching, kissing, or embracing the subordinate.
Friendly physical contact is crucial in maintaining good relationships among chimpanzees. For this reason, social grooming is probably the most important social behavior, serving to sustain or improve friendships within the community and to calm nervous or tense individuals. The grin of fear seen in frightened chimpanzees may be similar to the nervous smile given by humans when tense or in stressful situations. When angry, chimpanzees may stand upright, swagger, wave their arms, throw branches or rocks - all with bristling hair and often while screaming or with lips bunched in ferocious scowls. Male chimpanzees proclaim their dominance with spectacular charging displays during which they slap their hands, stamp with their feet, drag branches as they run, or hurl rocks. In doing so, they make themselves look as big and dangerous as they possibly can, and indeed may eventually intimidate a higher-ranking individual without having to fight.
Chimpanzees communicate using a wide variety of calls, postures and gestures. The food calls -- a mixture of grunts, barks, and pant hoots -- alert other chimpanzees to the location of a food source. A special excited intensity of these calls indicates that there has been a successful kill after a hunt. Each individual has his or her own distinctive pant-hoot, so that the caller can be identified. A loud, long, savage-sounding ‘wraaaa’ call is made when a chimpanzee comes across something unusual or dangerous. When young chimpanzees play, they emit breathy laughter. Soft grunts uttered by foraging or resting chimpanzees maintains communication within the group.
Chimpanzees live in social groups called communities or unit groups. At Gombe, there have been between 40 and 60 individuals in the main study community (Kasakela) since 1960. Communities may be larger in other areas, or may be reduced to very small remnant groups. Chimpanzees' social structure can be categorized as "fusion-fission", meaning they travel around in groups of up to six individuals. The organisational structure of these groups is constantly changing as individuals wander off on their own for period of time, or join other groups. At times, many of a community's members come together in large excited gatherings, usually when fruit is available in one part of the range, or when a sexually popular female comes into estrus. Mothers and dependent young up to the age of seven are always together. Some individuals travel together more often than others - such as siblings and pairs of male friends. Contact is maintained between members of scattered groups by means of the distance call: the pant hoot.
Within the community, a male hierarchy establishes social standing, with one dominant male as the alpha. Females have their own, somewhat confused, hierarchy. All adult males dominate all females. Consequently most disputes within a community can be resolved by threats rather than actual attacks. However, the males within a community regularly patrol their boundaries, and if they encounter individuals of a neighboring community they may attack with extreme brutality. The only individuals who can move freely between communities are adolescent females who have not yet given birth. They may transfer to a new community permanently or, having become pregnant, move back to their own natal group.
When a female is in estrus and sexually attractive and receptive to the males, the skin around her rump swells considerably and is clear pink. Females show their first very small sexual swellings at age eight or nine, but are not sexually attractive to the older males until they reach age 10 or 11. There is usually a two-year period of adolescent sterility before the female finally conceives. Spacing between births, provided the previous infant lives, is about five years.
Some females in estrus are more attractive to the males than others. A popular female may be accompanied by many or even all of the adult males in her community. Alternatively the dominant male may become possessive of her and prevent the other males from attempted mating. Another interesting mating pattern is the consortship, during which a male persuades a female to accompany him to some peripheral part of the community range. If he is able to keep her there, away from other males until the time of ovulation, he has a good chance of siring her child. Even low-ranking males can become fathers if they have the skill to lead a female away at a time in her reproductive cycle when she is not interesting to the high-ranking males. At Gombe, chimpanzee males may be capable of reproduction at age 12 or 13, but are not socially mature until a few years later.