[Corvidae are able to understand the logical structure in string-pulling tasks]

The ability of the Corvidae to understand the logical structure in string-pulling tasks was studied in a set of experiments with varied position of strings. It was demonstrated that some hooded crows (Corvus cornix L.) and common ravens (Corvus corax L.) successfully completed the tasks where the strings were not intersected but placed so that the bait was positioned opposite the forepart of the empty string. Hooded crows also solved the task where the baits were attached to both strings, but one of the strings was disrupted. The task with two intersected strings where the bait was positioned opposite the forepart of the empty string was not solved by the crows. The results suggest the ability of both examined species to grasp the logical structure of such kind of tasks.