Abstract
One of the mysteries of animal problem-solving is the extent to which animals mentally represent problems in their minds. Humans can imagine both the solution to a problem and the stages along the way [1-3], such as when we plan one or two moves ahead in chess. The extent to which other animals can do the same is far less clear [4-25]. Here, we presented New Caledonian crows with a series of metatool problems where each stage was out of sight of the others and the crows had to avoid either a distractor apparatus containing a non-functional tool or a non-functional apparatus containing a functional tool. Crows were able to mentally represent the sub-goals and goals of metatool problems: crows kept in mind the location and identities of out-of-sight tools and apparatuses while planning and performing a sequence of tool behaviors. This provides the first conclusive evidence that birds can plan several moves ahead while using tools.