Stone the crows! Birds show Aesop's ancient fable is fact

Published on Thursday 6 August 2009 22:03

A FAMOUS Aesop's fable about a canny crow with a knowledge of physics is more than just folklore, scientists have shown.

Researchers found that rooks, members of the crow family, can use stones to raise the level of water in a container – just like the bird in the tale The Crow and the Pitcher.

In the story, written thousands of years ago by the Ethiopian slave Aesop, a thirsty crow finds a pitcher containing too little water for his beak to reach.

He solves the problem by throwing pebbles into the pitcher one by one, until the water level rises high enough for him to drink.

A similar challenge faced the rooks studied by the appropriately named Cambridge University zoologist Christopher Bird.

In a series of tests, the four rooks named Cook, Fry, Connelly and Monroe were offered a tempting treat – a juicy worm floating on the surface of water in a vertical tube.

To start with, the worm was out of reach. Videos of the experiments show the birds examining the tube from different angles, appearing to think the problem through.

Then the researchers provide a solution in the form of a handful of pebbles.

The rooks can be seen picking up the stones and dropping them into the tube to raise the water level and bring the worm within reach.

Cook and Fry succeeded straightaway, while Connelly and Monroe took two attempts.

The birds appeared to estimate how many pebbles were needed from the outset.

Rather than try for the worm after each stone was dropped, they waited until the time seemed right.

They also selected larger stones over smaller ones, for greater effect.

In other experiments, the rooks quickly understood that sawdust cannot be displaced in the same way as water.

Rooks and crows both belong to the corvid family.

"Corvids are remarkably intelligent, and in many ways rival the great apes in their physical intelligence and ability to solve problems," said Mr Bird, a Phd student.

"This is remarkable considering their brain is so different to the great apes'."

One corvid species, the Caledonian crow, is famed for its ability to make and use twig and leaf tools in the wild.

However, tool-use has never been known in wild rooks.

"Wild tool-use appears to be dependent on motivation," said Mr Bird.

"Rooks do not use tools in the wild because they do not need to, not because they can't.

"They have access to other food that can be acquired without using tools."

The only animal believed to have completed a similar fluid-mechanics task is the orangutan, he said.

The apes were reported to have brought a peanut within their grasp by spitting water into a tube.

Previously, Mr Bird showed rooks can use sticks as tools and fashion hooks out of wire to retrieve food.

The latest research is reported in the journal Current Biology.

The fable

A CROW, half-dead with thirst, came upon a Pitcher which had once been full of water; but when the Crow put its beak into the mouth of the Pitcher he found that only very little water was left in it, and that he could not reach far enough down to get at it.

He tried, and he tried, but at last had to give up in despair.

Then a thought came to him, and he took a pebble and dropped it into the Pitcher.

Then he took another pebble and dropped it into the Pitcher.

Then he took another pebble and dropped that into the Pitcher.

Then he took another pebble and dropped that into the Pitcher.

Then he took another pebble and dropped that into the Pitcher.

Then he took another pebble and dropped that into the Pitcher.

At last, at last, he saw the water mount up near him, and after casting in a few more pebbles he was able to quench his thirst and save his life.

"Little by little does the trick."