Hook innovation boosts foraging efficiency in tool-using crows

Abstract

The New Caledonian crow is the only non-human animal known to craft hooked tools in the wild, but the ecological benefit of these relatively complex tools remains unknown. Here, we show that crows acquire food several times faster when using hooked rather than non-hooked tools, regardless of tool material, prey type and extraction context. This implies that small changes to tool shape can strongly affect energy-intake rates, highlighting a powerful driver for technological advancement.

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Fig. 1: Ecological benefit of hook innovation in New Caledonian crows.

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Acknowledgements

We thank the Province Sud and SEM Mwe Ara, New Caledonia, for research permits and access to our study site and facilities, T. Mennesson and C. Lambert for invaluable support, S. Wischnewski, J. van der Wal, Z. Burns and several field assistants for help with bird trapping and husbandry and/or running trials, and A. Péter for technical advice on Solomon Coder software. We are grateful to J. Call, L. Dean, K. Laland, A. Magurran and L. Rendell for providing insightful and constructive comments on earlier drafts. Experiments were approved by Oxford University’s local ethical review committee before the group’s transfer to the University of St Andrews. The study was funded through a Biotechnology and Biological Sciences Research Council David Phillips Fellowship (grant BB/G023913/2 to C.R.) and PhD studentships from the Biotechnology and Biological Sciences Research Council (B.C.K.) and the Japan Student Services Organization (S.S.).

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Contributions

J.J.H.S.C. and C.R. conceived, designed and planned the experiments. B.C.K., S.S., J.J.H.S.C. and C.R. conducted fieldwork and ran experimental trials. C.G.H. and J.J.H.S.C. scored videos, and S.S. and J.J.H.S.C. extracted data. J.J.H.S.C. and N.C. performed the statistical analyses. J.J.H.S.C. and C.R. wrote the manuscript, which was approved by all authors. C.R. secured funding and supervised the project.

Corresponding authors

Correspondence to James J. H. St Clair or Christian Rutz.

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The authors declare no competing financial interests.

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Supplementary information

Videos

Supplementary Video 1

Hooked stick tool manufacture by a captive New Caledonian crow (sub-adult female subject HA7).

Supplementary Video 2

Probing behaviour expressed by captive New Caledonian crows (video screen), and the method of scoring using Solomon Coder software. Probing state (first column) is opened for a given hole when the tip of the tool is inserted and closed when the tool is removed. Extraction data are scored in subsequent columns. The total duration of probing required to secure the food is later summed for each hole.

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St Clair, J.J.H., Klump, B.C., Sugasawa, S. et al. Hook innovation boosts foraging efficiency in tool-using crows. Nat Ecol Evol 2, 441–444 (2018). https://doi.org/10.1038/s41559-017-0429-7

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