In a modern retelling of one of Aesop's fables, researchers in England have shown that members of the crow family can use tools to retrieve a worm that they wouldn't otherwise be able to reach.
In "The Crow and the Pitcher," Aesop wrote of a thirsty bird confronted with a half-full pitcher of water. When the bird discovered that the water level was too low to reach, he dropped stones in to raise the level until it was high enough to quench his thirst.
Aptly named zoologist Christopher David Bird of University of Cambridge showed that rooks, members of the crow family, could perform the same task, dropping stones into a tall glass beaker to retrieve a floating wax worm.
The results, reported this week in the journal Current Biology, are not totally unexpected: Crows have previously been shown to use leaves and sticks as probes to dig out grubs, and shells and rocks as hammers to break open prey or as plugs to form pools of water for drinking.
Bird and his colleague Nathan Emery of Queen Mary University of London tested four 5-year-old, hand-raised rooks, confronting them with the flask and a pile of stones. Two immediately figured out how to get the worm, and two got it on the second try.
The birds appeared to calculate how high the water had to rise, and put in only enough stones to raise the water to that level, not stopping to try to reach the worm after each stone. They also figured out quickly that larger stones would raise the water more quickly.
The only other animals known to have accomplished a similar feat are orangutans, which have been shown to carry water in their mouths to fill a pitcher so they can reach a floating peanut. But the rooks' feat is more impressive, Bird argued, because their brains are much smaller than those of orangutans.
One of the rooks also displayed a different type of learning ability: When she got sick from eating one of the wax worms, she stopped participating in the experiments.