Fig. 3

Influence of raw-material properties on the tool-manufacture behaviour of New Caledonian crows in Experiment 2. a Percentage of crows manufacturing tools from the stems provided in choice trials (n = 14 for material score 4.5 [‘matched’ plus ‘control’ stems]; n = 7 for all other material scores; dark grey: hooked stick tools, light grey: non-hooked stick tools). b Order (mean ± standard error) in which stems were chosen by crows (excluding control stems, but including stems which were pulled out of the log or used to make non-hooked stick tools). Black values are for all stems, with unchosen stems being assigned a value of 8 (n = 7 for each material score), and grey values are for chosen stems only (n = 1–7). c Time to release the basic tool (only hooked stick tools, with stems that were pulled out of the log excluded; n = 1–12)