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.