Strong between-site variation in New Caledonian crows' use of hook-tool-making materials.

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.