Hook tool manufacture in New Caledonian crows: behavioural variation and the influence of raw materials

• DOI: 10.1186/s12915-015-0204-7
• Publication Date: 2015-11-18T09:21:54Z
• Authors: Barbara C. Klump; Shoko Sugasawa; James J. H. St Clair; Christian Rutz
• Keywords: Hook; Variation (astronomy)

New Caledonian crows use a range of foraging tools, and are the only non-human species known to craft hooks. Based on small number observations, their manufacture hooked stick tools has previously been described as complex, multi-stage process. Tool behaviour is shaped by genetic predispositions, individual social learning, and/or ecological influences, but disentangling relative contributions these factors remains major research challenge. The properties raw materials an obvious, largely overlooked, source variation in tool-manufacture behaviour. We conducted experiments with wild-caught crows, assess tool making, investigate how raw-material affect In Experiment 1, we showed that crows' can be much more variable than thought (85 18 subjects), involve two newly-discovered behaviours: 'pulling' for detaching stems bending shaft. Crows' manufactures varied significantly: different action types employed; time spent processing hook shaft; structure sequences. 2, examined interaction properties, using novel paradigm enabled us determine subjects' rank-ordered preferences (42 7 subjects). Plant influenced: order which selected stems; whether was manufactured; required release basic tool; and, possibly, technique, behavioural actions, aspects Results from 2 suggested at least part natural observed 1 due effect properties. Our discovery behaviours indicates plausible scenario evolutionary origins, gradual refinement, making. Furthermore, our experimental demonstration link between provides alternative hypothesis explaining regional differences some primate species.