New Caledonian crows keep ‘valuable’ hooked tools safer than basic non-hooked tools
- Centre for Biological Diversity, School of Biology, United Kingdom
- Cognitive and Cultural Ecology Group, Max Planck Institute of Animal Behavior, Germany
Figures
Figure 1
Tool types used by New Caledonian crows and experimental treatments of Experiment 2.
(a) Crows in our study population are known to use two tool types – non-hooked stick tools (top) and hooked stick tools (bottom). (b) Treatments in Experiment 2. To assess crows’ tool-placement behaviour following successful food extractions, we presented them with different materials: 100 sticks and leaf petioles (Treatment 2.A), 10 stems of Desmanthus virgatus (the preferred raw material for hooked stick tool manufacture in this population) with multiple forks suitable for tool manufacture (Treatment 2.B), 3 non-hooked stick tools researcher-made from D. virgatus (Treatment 2.C), and 3 hooked stick tools researcher-made from D. virgatus (Treatment 2.D). Arrows indicate differences between treatments, and the layout of treatments is the same as in Figure 3, to facilitate comparison. Figure adapted from St Clair et al., 2018, but note different labelling of treatments (2.A in the present study → 1b in earlier study; 2.B → 1a; 2.C → 2b; 2.D → 2a).
© 2018, St Clair et al. Image credit panel (a): these photos are reproduced from Figure 1A from St Clair et al., 2018; they are not covered by the CC-BY 4.0 licence, and further reproduction of this panel would require permission from the copyright holder.
Figure 2 with 1 supplement
New Caledonian crows’ choice of different tool types in Experiment 1.
In each of the two treatments, 21 tools were presented simultaneously; Treatment 1.A: 2 stick tools researcher-made from Desmanthus virgatus (one hooked, one non-hooked), 19 non-hooked stick tools sourced from leaf litter (sticks and leaf petioles); Treatment 1.B: 20 stick tools researcher-made from D. virgatus (1 hooked, 19 non-hooked), 1 leaf petiole (for an example set of tools, see Figure 2—figure supplement 1). Values above bars indicate the number of crows contributing valid data; each subject contributed one datum per column. Adjusted p-values (Bonferroni correction for multiple testing) indicate the probabilities that the hooked stick tool was picked up, transported to the food log, deployed, and successfully used (extraction of bait) at the observed frequency by chance alone. The dashed line (4.76%) represents the random expectation of choosing any given one of the 21 presented tools.
Figure 2—figure supplement 1
Tools presented in Experiment 1 to New Caledonian crow ‘APO’, photographed on grid paper.
(a) Treatment 1.A, from left to right: 19 twigs and leaf petioles, 1 non-hooked stick tool researcher-made from Desmanthus virgatus, and 1 hooked stick tool researcher-made from D. virgatus. (b) Treatment 1.B, from left to right: 19 non-hooked stick tools researcher-made from D. virgatus, 1 leaf petiole, and 1 hooked stick tool researcher-made from D. virgatus. Tools made from D. virgatus are generally more flexible and thinner in diameter compared to twigs and leaf petioles.
Figure 3
New Caledonian crows’ handling of different tool types in Experiment 2.
Placement of tools (percentage of cases) for crow-sourced (Treatment 2.A) and researcher-supplied (Treatment 2.C) non-hooked stick tools (shown in the top panels), and for self-manufactured (Treatment 2.B) and researcher-supplied (Treatment 2.D) hooked stick tools (shown in the bottom panels). Please see the main text and Figure 1 (which has the same layout as this figure) for further information on treatments. Blue colours indicate secure placement of tools (‘safekeeping’), while orange and red colours indicate unsecure placement. Subjects are identified at the top by their alpha-numerical ring codes, and values above bar charts indicate the number of prey extractions for a given treatment, for which tool placement was established; the rightmost bars for each treatment (marked ‘all’) show data pooled across all birds. Subjects are ordered by gape score (% black colouration; older birds usually have darker gapes). Results of comparisons between treatments are indicated by greater than or approximately equal signs, with p-values given for both the level (i.e., whether or not tools were kept safe) and the mode (i.e., how tools were kept safe – specifically, whether or not they were stored in holes) of safekeeping. For further details on statistical results, see main text and Supplementary file 1c.
Additional files
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Transparent reporting form
- https://cdn.elifesciences.org/articles/64829/elife-64829-transrepform1-v1.pdf
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Supplementary file 1
Demographic information for New Caledonian crows trapped and tested as well as GLMM results.
- https://cdn.elifesciences.org/articles/64829/elife-64829-supp1-v1.docx
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Source data 1
Source data for Experiment 2.
- https://cdn.elifesciences.org/articles/64829/elife-64829-supp2-v1.csv
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Source code 1
Source code for Experiment 2.
- https://cdn.elifesciences.org/articles/64829/elife-64829-supp3-v1.zip
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New Caledonian crows keep ‘valuable’ hooked tools safer than basic non-hooked tools
eLife 10:e64829.
https://doi.org/10.7554/eLife.64829
