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Researchers in England have found that at least one of Aesop’s fables is not far from fact. In their experiments, Christopher Bird of the University of Cambridge and Nathan Emery of Queen Mary University of London set out to determine whether the plot line behind Aesop’s “The Crow and The Pitcher” could be replicated using captive rooks, which, like crows and ravens, are also members of the corvid family.
In the fable, a crow comes upon a pitcher of water. Though the crow is thirsty, it cannot reach its beak far enough into the pitcher to drink the water. After giving it some thought, the crow decides to drop stones into the pitcher, causing the water level to rise. After adding enough stones, the crow is able to successfully drink from the pitcher.
Previous experiments have shown that other members of the corvid family are adept at solving complex problems by making tools. For example, in one experiment, crows were shown a set-up which included a tube containing a treat-filled pail at its bottom and a straight wire. The crows were able to determine that in order to get the pail out of the tube, they had to bend the wire so that it could hook the pail’s handle and pull the pail out of the tube.
Dr. Bird and Dr. Emery’s basic set-up included a pile of stones and a clear tube filled with water with a worm floating on top. Their experimental design contained three different scenarios. In the first scenario, the amount of water in the tube varied. In the second scenario, the size of the stones varied. In the third scenario, two tubes were presented–one filled with sawdust and the other with water.
The scientists tested the problem-solving skills of four rooks: Cook, Fry, Connelly, and Monroe. Of the four birds, all were successful in completing the task. In addition, the rooks were very accurate when problem-solving. After examining the set-up, each bird used the exact number of stones to raise the water level high enough so that the bird could reach the worm. The birds did not test whether the water level was high enough until the last stone was added to the tube. In the second scenario, the birds knew to choose the larger stones in order to accomplish the task faster. In the third scenario, the birds quickly learned that sawdust could not be displaced in the same way that water could be. When presented with a tube filled with water and one filled with sawdust, the birds opted to drop stones only into the water-filled tube in order to get the worm treat.
Unlike other members of the corvid family, rooks have never been observed using tools in the wild. According to Dr. Bird, the use of tools by animals in the wild depends on motivation. Therefore, rooks in the wild do not choose to use tools not because they can’t, but because, in their habitat, they do not need to.
The results of the scientists’ research were published online in the August 6, 2009 edition of the journal Current Biology.