The right tool for the job: what strategies do wild New Caledonian crows use?
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New Caledonian crows Corvus moneduloides (NC crows) display sophisticated tool manufacture in the wild, but the cognitive strategy underlying these skills is poorly understood. Here, we investigate what strategy two free-living NC crows used in response to a tool-length task. The crows manufactured tools to extract food from vertical holes of different depths. The first tools they made in visits were of a similar length regardless of the hole depth. The typical length was usually too short to extract food from the deep holes, which ruled out a strategy of immediate causal inference on the first attempt in a trial. When the first tool failed, the crows made second tools significantly longer than the unsuccessful first tools. There was no evidence that the crows made the lengths of first tools to directly match hole depth. We argue that NC crows may generally use a two-stage heuristic strategy to solve tool problems and that performance on the first attempt in a trial is not necessarily the ‘gold standard’ for assessing folk physics.
KeywordsCognition Folk physics New Caledonian crows Tool manufacture and use
We thank Emile Hautcoeur for access to his land at Sarraméa. Staff in the Political Section of the provincial administration on Maré provided valuable help with access to forest and William Wadrobert kindly allowed us to work on his family's land in Wabao District. Daniel Houmbouy (Province des Iles Loyauté) gave us permission to work on Maré, and Etienne DuTailly provided us with accommodation and assistance in Nouméa. We thank Mick Sibley for preparing DVD versions of the footage and Michael Corballis and Alex Taylor for helpful comments on the manuscript. This research was funded by an Auckland University Emerging Researchers Grant (G.R.H.), the New Zealand Marsden Fund (R.D.G. and G.R.H.) and a Thomas J. Watson Fellowship (R.B.R.). The research reported in this paper was approved by the University of Auckland Animal Ethics committee (approval #R172). We thank Shige Watanabe and Ludwig Huber for inviting us to participate in the Animal Logic symposium in Vienna, and Alex Weir and Alex Kacelnik for an exchange of crow manuscripts submitted to this volume.
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