Further Observations on the Use of Ladders in a Group of Young Chimpanzees

Abstract

Although no comparable behaviors have as yet been reported in wild chimpanzees, most captive chimpanzees easily learn to stand a loose branch or other elongated object vertically, and use it for vaulting or climbing. The present animals went beyond this: they also learned to brace the top of the branch against a vertical structure (wall, tree, etc.), and thus create a ‘ladder’ which would remain standing indefinitely and which could be used simultanously by several animals. An earlier paper described the origin and first varieties of ladder using; the present paper describes a new variety, namely escape over the 5.5 m high fence. No deliberate training was involved at any stage of our research.

Tool Use in a Group of Captive Chimpanzees I. Escape

“…A chimpanzee in Munich Zoo placed two automobile tyres upright, one atop the other, against the wall of a dry moat and climbed out of the enclosure (LORENZ, personal communication). The present report, taken with MENZEL'S (1972MENZEL'S ( , 1973 earlier accounts, provides the most complete description yet published of the development of a variety of tool using activities leading to persistent escape attempts and some successes.…”

“…H e was fortunate enough to observe this process from its beginnings and reported individual differences and the diffusion of the skills through social learning. Near the end of MENZEL'S observations in June, 1971, the chimpanzees began to use pole-ladders to escape from the field enclosure (MENZEL 1973). Our observations below are intended to supplement and update his report, describing developments from July, 1971, to September, 1972 From the beginning the chimpanzees made ladders from natural tree branches which they obtained from the 25 pine trees growing in the field enclosure.…”

“…While living in the enclosure the chimpanzees had been tested daily in experiments on group organization and communication (MENZEL 1971(MENZEL , 1974. However, beginning six months before the observation period and continuing through its seven months, the chimpanzee group was left to its own devices in what was by captive standards a spacious, semi-naturalistic environment.…”

Standing and climbing a pole by members of a captive group of Japanese monkeys

“…It is well known that juvenile members are more reactive to novel objects than adult members (MENZEL, 1966) and perform various manipulation patterns with novel objects (TORIGOE, 1987). "Standing and climbing a pole" by the three monkeys was frequently performed soon after the presentation of novel elongated objects.…”

“…MENZEL (1972MENZEL ( , 1973 reported one member in a captive group of chimpanzees which learned to create a "ladder" by standing a pole against a vertical structure, and thereby to gain access to windows, trees, and other high places. This "ladder" would remain standing indefinitely and be used simultaneously by several animals.…”