Spontaneous sponge-making in captive chimpanzees

Abstract

An attempt was made at reduplicating in captivity the conditions under which sponge-making behavior is known to occur among chimpanzees in the wild. A bottle filled with fruit juice to a depth of 3 cm was fastened outside the cage of two young female chimpanzees and leafy branches were provided in the cage. Over 21 experimental sessions of one hour each, the most proficient animal was observed to use the branches in a number of ways for absorbing and drinking the juice. Most commonly, a branch was broken, its leaves removed, the extremity inserted repeatedly into a bottle and withdrawn to lick the adhering juice. At the moset developed stage, the extremity of the branch was chewed over a length of 2 cm and reduced to a frayed condition that was found to increase four times its absorbing capacity. Similarities and differences in Gombe Stream and in this experimental situation are indicated. The sponging behavior as practised by zoo chimpanzees indicates that the example of the mother is by no means necessary for the habit to appear inyoung animals. This observation raises the question wheather the acquisition of so-called protocultural habits does not rely as much, at least, on independent reinvention as on transmission through imitation learning. It is concluded that the sponge-making behavior observed in Gomobe can most parisimioniously be interpreted as an incidental corollary of a highly variable and potentially meaningul expression of the chimpanzee's behavioral resourcefullness.