The crafting of hook tools by wild New Caledonian crows

TLDR

Tool crafting involves selecting raw material, trimming, and sculpting, and its evolution enables open‑ended tool development, while prior work noted New Caledonian crows use hooked leafy twigs, a practice distinct from other species that lack sculpting. The study describes how an adult crow and its juvenile produced ten hooked‑twig tools. They followed a consistent three‑step process of selecting material, trimming, and extensively sculpting the hook. The crows produced a diverse array of hooked twig tools, showing that their fine, three‑stage crafting process narrows a previously claimed human‑animal difference.

Abstract

The 'crafting' of tools involves (i) selection of appropriate raw material, (ii) preparatory trimming and (iii) fine, three–dimensional sculpting. Its evolution is technologically important because it allows the open–ended development of tools. New Caledonian crows manufacture an impressive range of stick and leaf tools. We previously reported that their toolkit included hooked implements made from leafy twigs, although their manufacture had never been closely observed. We describe the manufacture of 10 hooked–twig tools by an adult crow and its dependent juvenile. To make all 10 tools, the crows carried out a relatively invariant three–step sequence of complex manipulations that involved (i) the selection of raw material, (ii) trimming and (iii) a lengthy sculpting of the hook. Hooked–twig manufacture contrasts with the lack of sculpting in the making of wooden tools by other non–humans such as chimpanzees and woodpecker finches. This fine, three–stage crafting process removes another alleged difference between humans and other animals.