Gombe Stream National Park
Some of the most interesting social behavior happens when chimpanzees meet and greet each other after being separated for a while, and have to reestablish their relationships. This happens every day in chimpanzee society, as small groups of community members merge and split.
Often when adult males join a group, they arrive with hair erect, a sign of tension and readiness to fight. They may break into a charging display, swaying bushes or dragging branches, hurling rocks, stamping on the ground, even hitting anyone who does not get away in time.
Meanwhile, lower-ranking chimps such as females and young males pant-grunt ("uh-uh-uh-uh", a sign of submission) or may even scream with bared teeth, a sign of fear. Usually the males then settle down, still bristling, and other chimps cautiously approach them. A female typically greets a male by pant-grunting and presenting her rear to him. He then inspects her anogenital area to determine her hormonal condition, or may just give her a reassuring touch. Sometimes, chimps may kiss or embrace one another in greeting or for reassurance.
After such preliminaries, chimps often settle down to a grooming session, which may be as short as a minute or as long as several hours. Many people think that the purpose of grooming is to catch parasites or to clean the coat, which it certainly does. However, it also has a very important social function, that of calming or relaxing the one who is groomed. It is an excellent way to soothe the tension that accompanies an encounter. In our own society, polite conversation has replaced physical grooming, but both may serve similar functions.
Females groom mainly with their immediate family, and with certain males. Males groom mostly with other males; elderly and high-ranking males receive the most grooming. Males whose relationship is tense may spend long sessions grooming, but those whose relationship is hostile or unresolved do not groom together.
In relaxed situations, young chimps spend much time playing. Infants at first play largely with objects, or with their mothers and older siblings who gently tickle and wrestle with them. Juveniles play more vigorously with wrestling and chasing. When playing, chimps show a play face, with the lower teeth bared, and they give hoarse panting laughter. Even adult chimps play together on rare occasions.
An oestrous female often attracts a group of males. She may mate with any of them, even infants and juveniles, or a high-ranking male may monopolize her. A male initiates mating by showing unmistakable signs of his readiness, and beckoning to the female or shaking a branch. Then the female crouches and presents to him. (Or, she herself may initiate mating by crouching and presenting to the male). Copulation lasts only a few seconds; the female squeaks or squeals and the male may pant softly. The female's child, or any other infant or juvenile, sometimes"interferes" by trying to get between the pair and pushing or pulling at the male's face. This is generally ignored. During extreme excitement, you may see males mounting males, or females on females, but this has nothing to do with mating; it is more a way of seeking reassurance.
At the end of the day, and occasionally for a daytime"siesta", each chimp prepares a nest in which to sleep. Normally, a nest is used only once, but sometimes old nests are improved and re-used. Standing on a branch, the chimp bends leafy branches and twigs towards itself, breaking them or pressing them down to form a springy platform of leaves and twigs. A mother shares her nest with her infant, but weaned juveniles sleep alone. Members of a group may nest in the same tree if there is room, or in adjacent trees. Usually chimps sleep all night, sometimes waking to give a chorus of hoots, but on moonlit nights they may feed close to the nest.
Special Thanks to Thomson Safaris and Tanzania National Parks for contributing Tanzanian information.
Details mentioned in this article were accurate at the time of publication