Complex cognition and behavioural innovation in New Caledonian crows

TLDR

Apes, corvids, and parrots exhibit high rates of behavioural innovation, but it remains unclear whether this arises from cognition more complex than simple learning mechanisms. The study aimed to determine whether New Caledonian crows’ innovative behaviour is driven by complex cognition by presenting them with a novel three‑stage metatool problem. The task required crows to (i) pull a short stick from a string, (ii) use that stick to retrieve a long stick from a toolbox, and (iii) use the long stick to extract food from a hole. Crows that had experience with all three stages solved the problem on the first trial, while those with only string and tool use also succeeded, and their performance—unexplained by simple reinforcement—was consistent with transferring an abstract causal rule that out‑of‑reach objects can be accessed with a tool, indicating that high innovation rates may reflect complex cognitive abilities.

Abstract

Apes, corvids and parrots all show high rates of behavioural innovation in the wild. However, it is unclear whether this innovative behaviour is underpinned by cognition more complex than simple learning mechanisms. To investigate this question we presented New Caledonian crows with a novel three-stage metatool problem. The task involved three distinct stages: (i) obtaining a short stick by pulling up a string, (ii) using the short stick as a metatool to extract a long stick from a toolbox, and finally (iii) using the long stick to extract food from a hole. Crows with previous experience of the behaviours in stages 1–3 linked them into a novel sequence to solve the problem on the first trial. Crows with experience of only using string and tools to access food also successfully solved the problem. This innovative use of established behaviours in novel contexts was not based on resurgence, chaining and conditional reinforcement. Instead, the performance was consistent with the transfer of an abstract, causal rule: ‘out-of-reach objects can be accessed using a tool’. This suggests that high innovation rates in the wild may reflect complex cognitive abilities that supplement basic learning mechanisms.