Eight hooded crows (Corvus cornix L.) were tested for their ability to use a piston (a stick with two attached clear plates between which the food is enclosed such that moving the stick would move the food) to get the reward out of a transparent tube avoiding a trap. Six out of eight crows learned to use a piston to extract a food reward from a transparent non-trap tube. One out of these six birds successfully performed the task in which it had to avoid a trap to retrieve a reward, in the first trial showing spontaneous comprehending of the task structure. Four crows learned to perform this task using the trial-and-error method. To find out a mechanism these crows used to perform the task, birds were presented with two transfer tasks (tests) in which we changed the relative positions of components in the apparatus. We found out that crows performed transfer tasks using rather concrete rules than immediate estimation of the relative positions of the components in the apparatus.
