[New method of evaluation of reasoning ability in birds].

A study was made on 52 birds of five Corvidae species of the ability to solve an elementary logical problem proposed by L. V. Krushinsky and N. P. Popova for the assessment of non-verbal human thinking. In the problem the bait was placed in turn in each of twelve similar food cups located in one row and covered with lids. The first and second time the bird could detect the bait only by means of random search, while by the third presentation it obtained the information necessary and sufficient for errorless determination of the bait location. It was found that 25% of the studied birds coped with the problem, although some solutions were "incomplete" since along with errorless choices, the bird found the bait only after opening one or two empty cups, located near by. The data obtained attest that the Corvidae are capable of a determination of a discrete stimulus displacement schedule presented by the experimenter. This fact may be considered as one more evidence of a high level of the Corvidae reasoning ability, since the problem presents a greater degree of complexity as compared with the tests previously used.