Do wild New Caledonian crows (Corvus moneduloides) attend to the functional properties of their tools?
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New Caledonian crows are the most proficient non-hominin tool manufacturers but the cognition behind their remarkable skills remains largely unknown. Here we investigate if they attend to the functional properties of the tools that they routinely use in the wild. Pandanus tools have natural barbs along one edge that enable them to function as hooking implements when the barbs face backwards from the working tip. In experiment 1 we presented eight crows with either a non-functional (‘upside-down’) or a functional pandanus tool in a baited hole. Four of the crows never flipped the tools. The behaviour of the four flipping birds suggested that they had a strategy of flipping a tool when it was not working. Observations of two of the eight crows picking up pandanus tools at feeding tables in the wild supported the lack of attention to barb direction. In experiment 2 we gave six of the eight crows a choice of either a barbed or a barbless pandanus tool. Five of the crows chose tools at random, which further supported the findings in experiment 1 that the crows paid little or no attention to the barbs. In contrast, a third experiment found that seven out of eight crows flipped non-functional stick tools significantly more than functional ones. Our findings indicate that the crows do not consistently attend to the presence or orientation of barbs on pandanus tools. Successful pandanus tool use in the wild seems to rely on behavioural strategies formed through associative learning, including procedural knowledge about the sequence of operations required to make a successful pandanus tool.
KeywordsNew Caledonian crows Tool use Hooks Associative learning Folk physics
We thank William Wadrobert for kindly allowing us to work on his family’s land in Wabao District, Maré. Daniel Houmbouy (Province des Iles Loyauté) gave us permission to work on Maré. Mick Sibley prepared DVD versions of the footage and constructed the aviary. Michael Anderson and Mick Sibley assisted with the data collection. We thank Alex Taylor and Roland Rehm for comments on earlier drafts and Alex Weir and three anonymous referees for detailed comments on the submitted manuscript. Felipe Medina helped to improve the figures. We thank Gilles Dagostini (I.R.D., Nouméa) for identifying Olea paniculata. This research was funded by a grant from the New Zealand Marsden Fund (R.D.G. and G.R.H.). The research reported in this paper was approved by the University of Auckland Animal Ethics committee (approval # R375) and complies with the laws of New Caledonia.
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