The reasoning ability was investigated in 29 Corvidae birds. The experimental task consisted in finding a hidden bait, the task being based on the fact that volumetric bait could be hidden in a volumetric geometrical figure only and not in a flat one. Thus it was possible to value the bird's ability to operate the empirical dimensions of objects. It was found that although the structure of bird brain is basically different from that of mammals, Corvidae surpass carnivorous mammals (dogs and cats) in solving this problem, their ability to operate the dimensions of objects being developped almost as well as that of monkeys.