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Fig. 2 | BMC Biology

Fig. 2

From: Hook tool manufacture in New Caledonian crows: behavioural variation and the influence of raw materials

Fig. 2

New Caledonian crows’ manufacture of hooked stick tools in Experiment 1. a Stacked bars are 85 sequences of behavioural actions from 18 subjects. Actions are colour-coded, and grouped into three main stages: (1) release of the basic tool; (2) processing of the basic tool; and (3) deployment of the tool. Note that, when the subject first detaches the raw material at the hook shaft or the root shaft, it can carry out other actions before releasing the basic tool at the root shaft, the hook shaft, or the joint (Fig. 1f). Sequences are ordered from left to right according to subjects’ gape colouration (% black; older birds tend to have darker gapes – for details, see Methods) and identity (multiple sequences from the same bird are grouped together). Sequences during which crows stripped bark are marked with black bars at the top. For manufacture sequences of Experiment 2, see Additional file 6: Figure S1. b, c and d show, respectively, the number of action types per sequence, the time spent processing the hook, and the time spent bending the tool shaft, for 10 subjects that had each produced three or more sequences. Boxplots show, where applicable, the median (thick line), the first and third quartiles (lower and upper margins of box), an approximate 95 % confidence interval (whiskers), and outliers (empty circles)

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