Abstract

Only a handful of bird species are known to use foraging tools in the wild1. Amongst them, the New Caledonian crow (Corvus moneduloides) stands out with its sophisticated tool-making skills2,3. Despite considerable speculation, the evolutionary origins of this species’ remarkable tool behaviour remain largely unknown, not least because no naturally tool-using congeners have yet been identified that would enable informative comparisons4. Here we show that another tropical corvid, the ‘Alalā (C. hawaiiensis; Hawaiian crow), is a highly dexterous tool user. Although the ‘Alalā became extinct in the wild in the early 2000s, and currently survives only in captivity5, at least two lines of evidence suggest that tool use is part of the species’ natural behavioural repertoire: juveniles develop functional tool use without training, or social input from adults; and proficient tool use is a species-wide capacity. ‘Alalā and New Caledonian crows evolved in similar environments on remote tropical islands, yet are only distantly related6, suggesting that their technical abilities arose convergently. This supports the idea that avian foraging tool use is facilitated by ecological conditions typical of islands, such as reduced competition for embedded prey and low predation risk4,7. Our discovery creates exciting opportunities for comparative research on multiple tool-using and non-tool-using corvid species. Such work will in turn pave the way for replicated cross-taxonomic comparisons with the primate lineage, enabling valuable insights into the evolutionary origins of tool-using behaviour.

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Acknowledgements

We thank: the many people – far too many to name individually – who have prevented the ‘Alalaˉ’s extinction, and who are working tirelessly towards its successful reintroduction into the wild; R. Fleischer for facilitating initial contacts; San Diego Zoo Global’s staff for assistance with experiments; C. Higgott for help with video scoring; D. Parker for constructing the consensus phylogeny; several photographers for providing images for Fig. 1; S. Thompson for help with graphic design; and G. Ruxton for statistical advice. Research was conducted with permission from San Diego Zoo Global’s IACUC animal welfare committee (Project ID#12-017), and with funding from the Biotechnology and Biological Sciences Research Council, UK (BBSRC; grant BB/G023913/2 to C.R., and studentship to B.C.K.), the University of St Andrews (C.R.), JASSO (S.S.), and the Royal Society of London (M.B.M.). Funding for the captive ‘Alala¯ propagation programme was provided by the U.S. Fish and Wildlife Service, Hawai‘i Division of Forestry and Wildlife, Moore Family Foundation, Marisla Foundation, several anonymous donors, and San Diego Zoo Global.

Author information

Affiliations

  1. Centre for Biological Diversity, School of Biology, University of St Andrews, Sir Harold Mitchell Building, St Andrews KY16 9TH, UK

    • Christian Rutz
    • , Barbara C. Klump
    • , Saskia Wischnewski
    • , Shoko Sugasawa
    • , Michael B. Morrissey
    •  & James J. H. St Clair
  2. Institute for Conservation Research, San Diego Zoo Global, PO Box 39, Volcano, Hawai‘i 96785, USA

    • Lisa Komarczyk
    • , Rosanna Leighton
    •  & Bryce M. Masuda
  3. Institute for Conservation Research, San Diego Zoo Global, 2375 Olinda Road, Makawao, Hawai‘i 96768, USA

    • Joshua Kramer
  4. Department of Physics and Centre for Networks and Collective Behaviour, University of Bath, Bath BA2 7AY, UK

    • Richard James
  5. Institute for Conservation Research, San Diego Zoo Global, 15600 San Pasqual Valley Road, Escondido, California 92027, USA

    • Richard A. Switzer

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Contributions

C.R. conceived of, initiated and led the project, and secured funding; R.A.S. and B.M.M. led the captive ‘Alalaˉ propagation programme, with support from R.L., J.K. and L.K.; C.R., J.J.H.S.C. and B.C.K. designed behavioural experiments; B.C.K., J.J.H.S.C. and C.R. conducted the species-wide tool-use assay, and L.K. performed the ontogeny experiment, with help from R.L., C.R., J.J.H.S.C. and B.C.K.; B.C.K. scored videos and extracted behavioural data, except for ontogeny trials, which were scored by S.W. and processed by S.S.; L.K., J.K., B.M.M. and C.R. collated and checked data on the life histories of captive birds; M.B.M. and B.C.K. assessed bird-performance data; R.J. and C.R. conducted social-diffusion simulations; C.R. and B.C.K. coordinated manuscript preparation, analysed data and prepared figures and videos; and C.R. wrote the manuscript, which was edited by B.C.K., J.J.H.S.C., R.J. and B.M.M., and approved by all co-authors.

Competing interests

The authors declare the following competing financial interests: five co-authors were (R.L., J.K., R.A.S.), or still are (L.K., B.M.M.), employees of San Diego Zoo Global, which is a not-for-profit organisation.

Corresponding author

Correspondence to Christian Rutz.

Reviewer Information Nature thanks T. Bugnyar, B. Kenward, S. Tebbich and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Extended data

Supplementary information

Videos

  1. 1.

    Spontaneous tool behaviour by an ‘Alalā

    This unedited scene shows the first presentation of the log set-up to adult male #134 (21 January 2013). Note that the log is a prototype that, compared to the final design later used for the species-wide behavioural assay, contained two additional holes.

  2. 2.

    Tool selectivity, modification and manufacture in ‘Alalā

    During experimental trials, many ‘Alalā were observed: a, to choose tools of appropriate dimensions; b, to replace tools that were not suitable; c, to transport non-supplied sticks to the set-up to be used as tools; to modify tools d, before or e, during deployment; or f, to handle, try and modify several different sticks during an extraction attempt. Tool manufacture behaviour included: g, snipping-off twigs from supplied dead branches; the production of h, bark flakes and i, wood splinters; and j, successive subtraction of material from non-supplied live plant material.

  3. 3.

    Ontogeny of tool-related behaviour in naïve juvenile ‘Alalā

    Functional tool behaviour can result from (a combination of) genetic predispositions, social learning, and individual learning. To investigate the relative importance of different processes, ‘naïve’ juveniles can be reared in captivity without opportunities to observe tool-use behaviour in proficient adult conspecifics, or even in humans. Under such controlled conditions, ‘Alalā chicks develop functional tool use over the first few months of life: a, first handling and carrying objects, including sticks, stones and other items; before b, inserting them into holes and crevices with gradually increasing proficiency (here, during a probe trial with several baited extraction tasks presented on a ‘platform’).

  4. 4.

    Historical recordings of ‘Alalā using tools

    Before the commencement of systematic behavioural experiments, staff at the KBCC and MBCC facilities had regularly observed ‘Alalā using tools. Following these opportunistic observations, on the 28 July 2011, four different birds were filmed using tools to reach for bait placed in a water bath (#114, #118, #135), or behind wire mesh (#146).

  5. 5.

    Eye movements in an ‘Alalā

    Like New Caledonian crows, ‘Alalā have unusually large eye-movement amplitudes. This video was taken when adult male #121 was trapped for a routine pre-breeding health check (19 March 2015) and presented with a neonate mouse to attract its attention.

  6. 6.

    Tool-use behaviour in crows

    Tool use of an adult male a, ‘Alalā and b, New Caledonian crow. ‘Alalā tend to hold stick tools in a frontal grip whereas New Caledonian crows prefer a transverse grip. c, Naturally non-tool-using rooks can be trained to use tools, but compared to most ‘Alalā and New Caledonian crows, they appear to handle sticks less dexterously (but note difference in extraction tasks provided).

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https://doi.org/10.1038/nature19103

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