National Geographic : 1963 Aug
The chimpanzees during much of the year move about in small groups of three to six animals. Such a group, I discovered from observation, may consist of adult males and females, of females and juveniles, of males only, or of a mixture of sexes and ages. During the day two or three small groups may join and move about together for a few hours or a few days. In certain seasons, main ly when some kind of favorite fruit is plentiful, I have often seen as many as 25 chimpanzees together. What makes the social pattern so compli cated is that the small groups are not stable. When two groups which have joined tempo rarily separate again, there has frequently been an exchange of individuals. Males often leave the group they are with to move about alone, subsequently joining another group or another lone male. This casual, free-and-easy grouping makes it harder to recognize individuals, yet it is essential to do so before one can even begin to understand the social pattern. From my mountaintop perch, I observed 282 how chimpanzees go to bed. Every night each one makes its own sleeping platform, or nest -except for the small infants, which sleep with their mothers until they are about three years old. Treetops Provide Springy Mattresses The construction of a nest, I found, is sim ple and takes only a couple of minutes. After choosing a suitable foundation, such as a hor izontal fork with several branches growing out, the chimpanzee stands on this and bends down a number of branches from each side so that the leafy ends rest across the foun dation. He holds them in place with his feet. Finally he bends in all the little leafy twigs that project around the nest, and the bed is ready. But the chimpanzee likes his comfort, and often, after lying down for a moment, he sits up and reaches out for a handful of leafy twigs which he pops under his head or some other part of his body. Then he settles down again with obvious satisfaction. One evening I sat quietly below a group of five chimpanzees that were feeding in a tree.