New Caledonian crows' basic tool procurement is guided by heuristics, not matching or tracking probe site characteristics

Contrasting findings made it unclear what cognitive processes New Caledonian crows use to procure suitable tools to solve tool tasks. Most previous studies suggested that their tool procurement is achieved by either trial and error or a simple heuristic. The latter provides a fast and cognitively efficient method for stable, routinized behaviour based on past experience with little or no deliberate decision-making. However, early papers by Chappell and Kacelnik reported that two New Caledonian crows procured tools after closely assessing the tool characteristics required for the task, thus using deliberate decision-making, or a ‘customized strategy’. Here, I tested eight New Caledonian crows to determine their default behaviour in basic tool procurement tasks as a check on whether or not they use customized strategies. I used two rigorous experiments closely based on Chappell and Kacelnik’s experiments. The crows did not use a customized strategy in either experiment, but their behaviour was clearly consistent with tool procurement predominantly guided by a familiarity heuristic. I discuss potential methodological issues that may have led to different conclusions in Chappell and Kacelnik’s studies. Heuristic-guided, routinized behaviour in tool procurement has potential implications for understanding how standardization occurs in the early evolution of complex tool manufacture, both in New Caledonian crows and early humans.