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NEW YORK – From the goose that laid the golden egg to the race between the tortoise and the hare, Aesop's fables are known for teaching moral lessons rather than literally being true. But a new study says at least one such tale might really have happened.

It's the fable about a thirsty crow. The bird comes across a pitcher with the water level too low for him to reach. The crow raises the water level by dropping stones into the pitcher. (Moral: Little by little does the trick, or in other retellings, necessity is the mother of invention.)

Now, scientists report that some relatives of crows called rooks used the same stone-dropping strategy to get at a floating worm. Results of experiments with three birds were published online Thursday by the journal Current Biology.

Rooks, like crows, had already been shown to use tools in previous experiments.

Christopher Bird of Cambridge University and a colleague exposed the rooks to a 6-inch-tall clear plastic tube containing water, with a worm on its surface. The birds used the stone-dropping trick spontaneously and appeared to estimate how many stones they would need. They learned quickly that larger stones work better.

In an accompanying commentary, Alex Taylor and Russell Gray of the University of Auckland in New Zealand noted that in an earlier experiment, the same birds had dropped a single stone into a tube to get food released at the bottom. So maybe they were just following that strategy again when they saw the tube in the new experiment, the scientists suggested.

But Bird's paper argued there's more to it: The rooks dropped multiple stones rather than just one before reaching for the worm, and they reached for it at the top of the tube rather than checking the bottom.

The researchers also said Aesop's crow might have actually been a rook, since both kinds of birds were called crows in the past.