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

James J H St Clair,Barbara C Klump,Shoko Sugasawa,Christian Rutz,Jessica E M Van Der Wal

doi:10.1111/bij.12757

James J H St Clair, Barbara C Klump + Show 3 more

Open Access

https://doi.org/10.1111/bij.12757

Copy DOI

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.

Highlights

Differences in behaviour between interconnected animal populations are of considerable interest to behavioural and evolutionary ecologists because they can indicate the action of powerful selective forces or cultural biases (Kawecki & Ebert, 2004; Laland & Janik, 2006; Lycett, Collard & McGrew, 2010)
We discovered that crows at one of our study sites almost exclusively use stems of a non-native but widespread shrub species, Desmanthus virgatus (Fig. 1A), as the raw material for hooked stick tool manufacture
The shape of the tool was not clearly visible, the actions resembled the latter stages of hooked stick tool manufacture

Summary

Introduction

Differences in behaviour between interconnected animal populations are of considerable interest to behavioural and evolutionary ecologists because they can indicate the action of powerful selective forces or cultural biases (Kawecki & Ebert, 2004; Laland & Janik, 2006; Lycett, Collard & McGrew, 2010). NC crows are known to manufacture tools from a wide range of plant materials, including leaves, grass stems, fern stolons, leaf petioles, and stem sections of various tree and vine species (Hunt, 1996, 2008; Troscianko, Bluff & Rutz, 2008). Their tools can be classified into those excised from the margins of screw-pine leaves (pandanus tools) and those made from parts of other plants (stick-type tools), with the latter subclassified into hooked and nonhooked stick tools (Rutz & St Clair, 2012). Raw materials usage can change over time, at least at the population level: the anthropogenically-introduced vine species Lantana camara has become the favoured raw material for tool manufacture at several sites (Hunt, 2008)

Methods

Results

Conclusion