Abstract
Betty the crow astonished the scientific world as she spontaneously crafted hook-tools from straight wire in order to lift a basket out of vertical tubes. Recently it was suggested that this species’ solution was strongly influenced by predispositions from behavioural routines from habitual hook-tool manufacture. Nevertheless, the task became a paradigm to investigate tool innovation. Considering that young humans had surprising difficulties with the task, it was yet unclear whether the innovation of a hooked tool would be feasible to primates that lacked habitual hook making. We thus tested five captive orangutans in a hook bending and unbending task. Orangutans are habitually tool-using primates that have been reported to use but not craft hooked tools for locomotion in the wild. Two orangutans spontaneously innovated hook tools and four unbent the wire from their first trial on. Pre-experience with ready-made hooks had some effect but did not lead to continuous success. Further subjects improved the hook-design feature when the task required the subjects to bent the hook at a steeper angle. Our results indicate that the ability to represent and manufacture tools according to a current need does not require stereotyped behavioural routines, but can indeed arise innovatively. Furthermore, the present study shows that the capacity for hook tool innovation is not limited to large brained birds within non-human animals.
Highlights
Tool-manufacture can be found in distantly related species but its occurrence is extremely rare[1]
Betty’s behaviour was for a long time considered a prime example of innovative tool manufacture in animals, a recent study showed that wild-caught New Caledonian crows employ the same motor action sequence that Betty used during hook bending to adjust the shaft of their tools during habitual tool making, thereby calling the innovative strength required to achieve her original solution to the original hook bending task into question[10,11]
The hook bending paradigm represents one of the rare cases in which comparative cognition was turned upside down[14]: a test that was originally developed from an accidental observation of a bird, that was later tested on other avian species was employed to test the development of tool innovation in human infants[15,16,17,18,19]
Summary
Tool-manufacture can be found in distantly related species but its occurrence is extremely rare[1]. Note that Betty’s behaviour still qualifies as innovative tool manufacture within our original definition since she applied an existing object modification to solve a novel problem and used a novel material while doing so. Another corvid, the rook and a parrot, the Goffin’s cockatoo were capable of finding a solution to the hook-bending task[12,13]. The fact that we humans take this long to develop the capacity for this type of tool innovation, coupled with us being the only habitually hook-tool using and hook-manufacturing primates[1], suggests that the ability to innovate hooks from pliant material may very well be limited to humans within primates
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