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Mack C, Uomini N. Modulation of behavioural laterality in wild New Caledonian crows ( Corvus moneduloides): Vocalization, age and function. Laterality 2022; 27:379-405. [PMID: 35833319 DOI: 10.1080/1357650x.2022.2098969] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The New Caledonian crow (Corvus moneduloides) is known for displaying a unique set of tool-related behaviours, with the bird's bill acting as an individually consistently lateralized effector. However, we still fail to understand how such laterality develops, is modulated or even if its expression is consistent across other behavioural categories. Creating the first ethogram for this species allowed us to examine laterality and vocalisations in a population of wild, free-flying New Caledonian crows using detailed analyses of close-up video footage. We revealed the existence of an overall strong left-sided bias during object manipulation only and which was driven by the adult crows of our focal population, the stabilization of individual preferences occurring during the birds' juvenile years. Individually, at least one crow showed consistent side biases to the right and left within different behavioural categories. Our findings highlight previously unknown variability in behavioural laterality in this species, thus advocating for further investigation. Specifically, we argue that a better understanding of the New Caledonian crow's biology and ecology is required if one wishes to pursue the promising comparative road that laterality could be connected to the evolution of tool-making.
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Affiliation(s)
- Cyrielle Mack
- Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
| | - Natalie Uomini
- Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
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2
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Steele MP, Neaves LE, Klump BC, St Clair JJH, Fernandes JRSM, Hequet V, Shaw P, Hollingsworth PM, Rutz C. DNA barcoding identifies cryptic animal tool materials. Proc Natl Acad Sci U S A 2021; 118:e2020699118. [PMID: 34253607 PMCID: PMC8307691 DOI: 10.1073/pnas.2020699118] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Some animals fashion tools or constructions out of plant materials to aid foraging, reproduction, self-maintenance, or protection. Their choice of raw materials can affect the structure and properties of the resulting artifacts, with considerable fitness consequences. Documenting animals' material preferences is challenging, however, as manufacture behavior is often difficult to observe directly, and materials may be processed so heavily that they lack identifying features. Here, we use DNA barcoding to identify, from just a few recovered tool specimens, the plant species New Caledonian crows (Corvus moneduloides) use for crafting elaborate hooked stick tools in one of our long-term study populations. The method succeeded where extensive fieldwork using an array of conventional approaches-including targeted observations, camera traps, radio-tracking, bird-mounted video cameras, and behavioral experiments with wild and temporarily captive subjects-had failed. We believe that DNA barcoding will prove useful for investigating many other tool and construction behaviors, helping to unlock significant research potential across a wide range of study systems.
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Affiliation(s)
- Matthew P Steele
- Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews KY16 9TH, United Kingdom
| | - Linda E Neaves
- Royal Botanic Garden Edinburgh, Edinburgh EH3 5LR, United Kingdom
- The Fenner School of Environment and Society, The Australian National University, Canberra, ACT 2600, Australia
| | - Barbara C Klump
- Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews KY16 9TH, United Kingdom
| | - James J H St Clair
- Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews KY16 9TH, United Kingdom
| | - Joana R S M Fernandes
- Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews KY16 9TH, United Kingdom
| | - Vanessa Hequet
- Institut de Recherche pour le Développement, Centre de Nouméa, 98848 Nouméa, New Caledonia, France
| | - Phil Shaw
- Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews KY16 9TH, United Kingdom
| | | | - Christian Rutz
- Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews KY16 9TH, United Kingdom;
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3
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Camacho-Alpízar A, Eckersley T, Lambert CT, Balasubramanian G, Guillette LM. If it ain't broke don't fix it: Breeding success affects nest-building decisions. Behav Processes 2021; 184:104336. [PMID: 33513432 DOI: 10.1016/j.beproc.2021.104336] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 01/13/2021] [Accepted: 01/19/2021] [Indexed: 11/27/2022]
Abstract
Observational studies in the wild suggest that birds select material to build their nests based on functional aspects of material that promote reproductive success. How birds select material for nest building from the variety of materials available in their environment is unclear. In the current laboratory experiment we manipulated breeding success (i.e. raising fledglings) of zebra finch (Taeniopygia guttata) pairs to test if this affects the subsequent selection of nest material between a familiar versus a novel material, that differ in structural properties. All birds experienced one breeding attempt using coconut fiber as nest material during which their breeding success was manipulated: half of the breeding pairs fledged their nestlings while the remaining pairs had their eggs removed to simulate nest failure. In a second nest-building attempt, all pairs were given access to both familiar nesting material (coconut fiber) and a novel nesting material (white cotton string). Pairs that were successful in their first breeding attempt built their second nest with significantly more familiar material compared to novel material. Pairs that were unsuccessful, however, incorporated similar amounts of familiar and novel material in their second attempt. Our results show that experiencing either a successful or an unsuccessful breeding attempt influences how birds select between familiar and novel material with different structural properties (e.g. flexibility, thickness) to build a second nest. Moreover, our experiment shows that learning from experience plays an important role for decision making in future structure-building endeavors.
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Affiliation(s)
| | - Tristan Eckersley
- Department of Psychology, University of Alberta, Edmonton, AB, Canada
| | - Connor T Lambert
- Department of Psychology, University of Alberta, Edmonton, AB, Canada
| | | | - Lauren M Guillette
- Department of Psychology, University of Alberta, Edmonton, AB, Canada; School of Biology, University of St Andrews, St Andrews, UK.
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4
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Klump BC, St Clair JJH, Rutz C. New Caledonian crows keep 'valuable' hooked tools safer than basic non-hooked tools. eLife 2021; 10:64829. [PMID: 34930523 PMCID: PMC8691834 DOI: 10.7554/elife.64829] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Accepted: 09/20/2021] [Indexed: 01/21/2023] Open
Abstract
The temporary storage and re-use of tools can significantly enhance foraging efficiency. New Caledonian crows in one of our study populations use two types of stick tools - hooked and non-hooked - which differ in raw material, manufacture costs, and foraging performance. Using a large sample of wild-caught, temporarily captive New Caledonian crows, we investigated experimentally whether individuals prefer one tool type over the other when given a choice and whether they take better care of their preferred tools between successive episodes of use, safely storing them underfoot or in nearby holes. Crows strongly preferred hooked stick tools made from Desmanthus virgatus stems over non-hooked stick tools. Importantly, this preference was also reflected in subsequent tool-handling behaviour, with subjects keeping hooked stick tools safe more often than non-hooked stick tools sourced from leaf litter. These results suggest that crows 'value' hooked stick tools, which are both costlier to procure and more efficient to use, more than non-hooked stick tools. Results from a series of control treatments suggested that crows altered their tool 'safekeeping' behaviour in response to a combination of factors, including tool type and raw material. To our knowledge, our study is the first to use safekeeping behaviour as a proxy for assessing how non-human animals value different tool types, establishing a novel paradigm for productive cross-taxonomic comparisons.
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Affiliation(s)
- Barbara C Klump
- Centre for Biological Diversity, School of BiologySt AndrewsUnited Kingdom,Cognitive and Cultural Ecology Group, Max Planck Institute of Animal BehaviorRadolfzell am BodenseeGermany
| | - James JH St Clair
- Centre for Biological Diversity, School of BiologySt AndrewsUnited Kingdom
| | - Christian Rutz
- Centre for Biological Diversity, School of BiologySt AndrewsUnited Kingdom
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Rutz C, Hunt GR. New Caledonian crows afford invaluable comparative insights into human cumulative technological culture. Behav Brain Sci 2020; 43:e177. [PMID: 32772983 DOI: 10.1017/s0140525x20000187] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The New Caledonian crow may be the only non-primate species exhibiting cumulative technological culture. Its foraging tools show clear signs of diversification and progressive refinement, and it seems likely that at least some tool-related information is passed across generations via social learning. Here, we explain how these remarkable birds can help us uncover the basic biological processes driving technological progress.
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Affiliation(s)
- Christian Rutz
- Centre for Biological Diversity, School of Biology, University of St Andrews, St AndrewsKY16 9TH, ://aviantooluse.org
- Radcliffe Institute for Advanced Study, Harvard University, CambridgeMA02138
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Klump BC. Of crows and tools. Science 2019; 366:965. [PMID: 31753993 DOI: 10.1126/science.aaz7775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Tool-using crows, culture, and what it means to be human
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Affiliation(s)
- Barbara C Klump
- Cognitive and Cultural Ecology Laboratory, Max Planck Institute of Animal Behavior, 78315 Radolfzell, Germany, and Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews, UK.
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7
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Klump BC, Cantat M, Rutz C. Raw-material selectivity in hook-tool-crafting New Caledonian crows. Biol Lett 2019; 15:20180836. [PMID: 30958132 DOI: 10.1098/rsbl.2018.0836] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Animals that manufacture foraging tools face the challenge of identifying suitable raw materials among a multitude of options. New Caledonian crows exhibit strong population-specific material preferences for the manufacture of hooked stick tools, but it is unknown how they identify their favourite plants. We investigated experimentally whether crows pay attention to the stems of plants (from which the tools are made) and/or their leaves (which are usually discarded during manufacture but may enable rapid and reliable species identification at a distance). Subjects were highly selective in choice trials with multiple plant species. Two additional treatments with experimental leaf-stem combinations revealed that birds can identify their preferred plant species by its stems alone, and possibly also its leaves. These findings encourage future experiments that investigate whether New Caledonian crows attend to features of the stem that are required for the production of efficient hooked stick tools. Our study provides one of the most detailed assessments to date of how non-human animals identify raw materials for tool manufacture.
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Affiliation(s)
- Barbara C Klump
- Centre for Biological Diversity, School of Biology, University of St Andrews , Sir Harold Mitchell Building, St Andrews KY16 9TH , UK
| | - Mathieu Cantat
- Centre for Biological Diversity, School of Biology, University of St Andrews , Sir Harold Mitchell Building, St Andrews KY16 9TH , UK
| | - Christian Rutz
- Centre for Biological Diversity, School of Biology, University of St Andrews , Sir Harold Mitchell Building, St Andrews KY16 9TH , UK
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Population Genomics and Structure of the Critically Endangered Mariana Crow ( Corvus kubaryi). Genes (Basel) 2019; 10:genes10030187. [PMID: 30832245 PMCID: PMC6471520 DOI: 10.3390/genes10030187] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Revised: 02/16/2019] [Accepted: 02/19/2019] [Indexed: 11/29/2022] Open
Abstract
The Mariana Crow, or Åga (Corvus kubaryi), is a critically endangered species (IUCN -International Union for Conservation of Nature), endemic to the islands of Guam and Rota in the Mariana Archipelago. It is locally extinct on Guam, and numbers have declined dramatically on Rota to a historical low of less than 55 breeding pairs throughout the island in 2013. Because of its extirpation on Guam and population decline on Rota, it is of critical importance to assess the genetic variation among individuals to assist ongoing recovery efforts. We conducted a population genomics analysis comparing the Guam and Rota populations and studied the genetic structure of the Rota population. We used blood samples from five birds from Guam and 78 birds from Rota. We identified 145,552 candidate single nucleotide variants (SNVs) from a genome sequence of an individual from Rota and selected a subset of these to develop an oligonucleotide in-solution capture assay. The Guam and Rota populations were genetically differentiated from each other. Crow populations sampled broadly across their range on Rota showed significant genetic structuring – a surprising result given the small size of this island and the good flight capabilities of the species. Knowledge of its genetic structure will help improve management strategies to help with its recovery.
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Klump BC, Masuda BM, St Clair JJH, Rutz C. Preliminary observations of tool-processing behaviour in Hawaiian crows Corvus hawaiiensis. Commun Integr Biol 2018; 11:e1509637. [PMID: 30534343 PMCID: PMC6284564 DOI: 10.1080/19420889.2018.1509637] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Accepted: 08/06/2018] [Indexed: 11/04/2022] Open
Abstract
Very few animal species habitually make and use foraging tools. We recently discovered that the Hawaiian crow is a highly skilled, natural tool user. Most captive adults in our experiment spontaneously used sticks to access out-of-reach food from a range of extraction tasks, exhibiting a surprising degree of dexterity. Moreover, many birds modified tools before or during deployment, and some even manufactured tools from raw materials. In this invited addendum article, we describe and discuss these observations in more detail. Our preliminary data, and comparisons with the better-studied New Caledonian crow, suggest that the Hawaiian crow has extensive tool-modification and manufacture abilities. To chart the full extent of the species’ natural tool-making repertoire, we have started conducting dedicated experiments where subjects are given access to suitable raw materials for tool manufacture, but not ready-to-use tools.
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Affiliation(s)
- Barbara C Klump
- Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews, UK
| | - Bryce M Masuda
- Institute for Conservation Research, San Diego Zoo Global, Volcano, Hawaii, USA
| | - James J H St Clair
- Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews, UK
| | - Christian Rutz
- Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews, UK
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Harrison RA, Whiten A. Chimpanzees ( Pan troglodytes) display limited behavioural flexibility when faced with a changing foraging task requiring tool use. PeerJ 2018; 6:e4366. [PMID: 29479495 PMCID: PMC5822838 DOI: 10.7717/peerj.4366] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 01/24/2018] [Indexed: 11/20/2022] Open
Abstract
Behavioural flexibility, the ability to alter behaviour in response to environmental feedback, and to relinquish previously successful solutions to problems, is a crucial ability in allowing organisms to adapt to novel environments and environmental change; it is essential to cumulative cultural change. To explore this ability in chimpanzees, 18 individuals (Pan troglodytes) were presented with an artificial foraging task consisting of a tube partially filled with juice that could be reached by hand or retrieved using tool materials to hand. Effective solutions were then restricted in the second phase of the study by narrowing the diameter of the tube, necessitating the abandonment of previously successful solutions. Chimpanzees showed limited behavioural flexibility in comparison to some previous studies, increasing their use of effective techniques, but also continuing to attempt solutions that had been rendered ineffective. This adds to a literature reporting divergent evidence for flexibility (the ability to alter behaviour in response to environmental feedback, and to relinquish previously successful solutions to problems) versus conservatism (a reluctance or inability to explore or adopt novel solutions to problems when a solution is already known) in apes.
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Affiliation(s)
- Rachel A Harrison
- Centre for Social Learning and Cognitive Evolution, School of Psychology & Neuroscience, University of St Andrews, St Andrews, United Kingdom.,School of Psychology, University of Birmingham, Birmingham, United Kingdom
| | - Andrew Whiten
- Centre for Social Learning and Cognitive Evolution, School of Psychology & Neuroscience, University of St Andrews, St Andrews, United Kingdom
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11
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Hook innovation boosts foraging efficiency in tool-using crows. Nat Ecol Evol 2018; 2:441-444. [DOI: 10.1038/s41559-017-0429-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Accepted: 11/27/2017] [Indexed: 11/08/2022]
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12
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Sugasawa S, Klump BC, St Clair JJ, Rutz C. Causes and Consequences of Tool Shape Variation in New Caledonian Crows. Curr Biol 2017; 27:3885-3890.e4. [DOI: 10.1016/j.cub.2017.11.028] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Revised: 11/08/2017] [Accepted: 11/09/2017] [Indexed: 10/18/2022]
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13
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Fujii JA, Ralls K, Tinker MT. Food abundance, prey morphology, and diet specialization influence individual sea otter tool use. Behav Ecol 2017. [DOI: 10.1093/beheco/arx011] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Rutz C, Sugasawa S, van der Wal JEM, Klump BC, St Clair JJH. Tool bending in New Caledonian crows. ROYAL SOCIETY OPEN SCIENCE 2016; 3:160439. [PMID: 27853622 PMCID: PMC5108972 DOI: 10.1098/rsos.160439] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Accepted: 07/08/2016] [Indexed: 06/06/2023]
Abstract
'Betty' the New Caledonian crow astonished the world when she 'spontaneously' bent straight pieces of garden wire into hooked foraging tools. Recent field experiments have revealed that tool bending is part of the species' natural behavioural repertoire, providing important context for interpreting Betty's iconic wire-bending feat. More generally, this discovery provides a compelling illustration of how natural history observations can inform laboratory-based research into the cognitive capacities of non-human animals.
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Adaptive bill morphology for enhanced tool manipulation in New Caledonian crows. Sci Rep 2016; 6:22776. [PMID: 26955788 PMCID: PMC4783770 DOI: 10.1038/srep22776] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 02/19/2016] [Indexed: 11/10/2022] Open
Abstract
Early increased sophistication of human tools is thought to be underpinned by adaptive morphology for efficient tool manipulation. Such adaptive specialisation is unknown in nonhuman primates but may have evolved in the New Caledonian crow, which has sophisticated tool manufacture. The straightness of its bill, for example, may be adaptive for enhanced visually-directed use of tools. Here, we examine in detail the shape and internal structure of the New Caledonian crow’s bill using Principal Components Analysis and Computed Tomography within a comparative framework. We found that the bill has a combination of interrelated shape and structural features unique within Corvus, and possibly birds generally. The upper mandible is relatively deep and short with a straight cutting edge, and the lower mandible is strengthened and upturned. These novel combined attributes would be functional for (i) counteracting the unique loading patterns acting on the bill when manipulating tools, (ii) a strong precision grip to hold tools securely, and (iii) enhanced visually-guided tool use. Our findings indicate that the New Caledonian crow’s innovative bill has been adapted for tool manipulation to at least some degree. Early increased sophistication of tools may require the co-evolution of morphology that provides improved manipulatory skills.
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St Clair JJH, Klump BC, van der Wal JEM, Sugasawa S, Rutz C. Strong between-site variation in New Caledonian crows' use of hook-tool-making materials. Biol J Linn Soc Lond 2016; 118:226-232. [PMID: 27867222 PMCID: PMC5111415 DOI: 10.1111/bij.12757] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Revised: 11/04/2015] [Accepted: 11/06/2015] [Indexed: 11/24/2022]
Abstract
Functional tool use requires the selection of appropriate raw materials. New Caledonian crows Corvus moneduloides are known for their extraordinary tool‐making behaviour, including the crafting of hooked stick tools from branched vegetation. We describe a surprisingly strong between‐site difference in the plant materials used by wild crows to manufacture these tools: crows at one study site use branches of the non‐native shrub Desmanthus virgatus, whereas only approximately 7 km away, birds apparently ignore this material in favour of the terminal twigs of an as‐yet‐unidentified tree species. Although it is likely that differences in local plant communities drive this striking pattern, it remains to be determined how and why crows develop such strong site‐specific preferences for certain raw materials.
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Affiliation(s)
- James J H St Clair
- Centre for Biological Diversity School of Biology University of St Andrews St Andrews KY16 9TH UK
| | - Barbara C Klump
- Centre for Biological Diversity School of Biology University of St Andrews St Andrews KY16 9TH UK
| | - Jessica E M van der Wal
- Centre for Biological Diversity School of Biology University of St Andrews St Andrews KY16 9TH UK
| | - Shoko Sugasawa
- Centre for Biological Diversity School of Biology University of St Andrews St Andrews KY16 9TH UK
| | - Christian Rutz
- Centre for Biological Diversity School of Biology University of St Andrews St Andrews KY16 9TH UK
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Klump BC, Sugasawa S, St Clair JJH, Rutz C. Hook tool manufacture in New Caledonian crows: behavioural variation and the influence of raw materials. BMC Biol 2015; 13:97. [PMID: 26582537 PMCID: PMC4650250 DOI: 10.1186/s12915-015-0204-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2015] [Accepted: 10/21/2015] [Indexed: 11/17/2022] Open
Abstract
Background New Caledonian crows use a range of foraging tools, and are the only non-human species known to craft hooks. Based on a small number of observations, their manufacture of hooked stick tools has previously been described as a complex, multi-stage process. Tool behaviour is shaped by genetic predispositions, individual and social learning, and/or ecological influences, but disentangling the relative contributions of these factors remains a major research challenge. The properties of raw materials are an obvious, but largely overlooked, source of variation in tool-manufacture behaviour. We conducted experiments with wild-caught New Caledonian crows, to assess variation in their hooked stick tool making, and to investigate how raw-material properties affect the manufacture process. Results In Experiment 1, we showed that New Caledonian crows’ manufacture of hooked stick tools can be much more variable than previously thought (85 tools by 18 subjects), and can involve two newly-discovered behaviours: ‘pulling’ for detaching stems and bending of the tool shaft. Crows’ tool manufactures varied significantly: in the number of different action types employed; in the time spent processing the hook and bending the tool shaft; and in the structure of processing sequences. In Experiment 2, we examined the interaction of crows with raw materials of different properties, using a novel paradigm that enabled us to determine subjects’ rank-ordered preferences (42 tools by 7 subjects). Plant properties influenced: the order in which crows selected stems; whether a hooked tool was manufactured; the time required to release a basic tool; and, possibly, the release technique, the number of behavioural actions, and aspects of processing behaviour. Results from Experiment 2 suggested that at least part of the natural behavioural variation observed in Experiment 1 is due to the effect of raw-material properties. Conclusions Our discovery of novel manufacture behaviours indicates a plausible scenario for the evolutionary origins, and gradual refinement, of New Caledonian crows’ hooked stick tool making. Furthermore, our experimental demonstration of a link between raw-material properties and aspects of tool manufacture provides an alternative hypothesis for explaining regional differences in tool behaviours observed in New Caledonian crows, and some primate species. Electronic supplementary material The online version of this article (doi:10.1186/s12915-015-0204-7) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Barbara C Klump
- Centre for Biological Diversity, School of Biology, University of St Andrews, Sir Harold Mitchell Building, St Andrews, KY16 9TH, UK.
| | - Shoko Sugasawa
- Centre for Biological Diversity, School of Biology, University of St Andrews, Sir Harold Mitchell Building, St Andrews, KY16 9TH, UK.
| | - James J H St Clair
- Centre for Biological Diversity, School of Biology, University of St Andrews, Sir Harold Mitchell Building, St Andrews, KY16 9TH, UK.
| | - Christian Rutz
- Centre for Biological Diversity, School of Biology, University of St Andrews, Sir Harold Mitchell Building, St Andrews, KY16 9TH, UK.
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