Crows are well known for their intelligence, and their cleverness was recognized centuries ago in Aesop’s tale of "The Crow and the Pitcher."

In the Greek fable, a thirsty crow drops stones into a pitcher to raise the level of water so he can drink.

Now research proves that such a task isn't just the stuff of stories.

A species of crow native to New Caledonia, an island off the coast of Australia, can solve such a puzzle. And the birds can do it as well as a 7-year-old human child.

For the study, scientists captured six of the crows, which are known for being the only non-primate that makes tools in the wild. New Caledonian crows often break off twigs or collect barbed leaves and use the objects as hooks to dig for insects.

Scientists trained the birds to pick up stones and then challenged them with different Aesop-inspired puzzles. In the challenges, cubes of meat attached to corks were placed in transparent tubes that were too deep for the crows to reach.

In one set-up, the crows were provided with two tubes: one partly filled with sand and another partly filled with water.

For the most part, the birds didn't bother with the tube of sand. Seventy-six percent of their efforts were focused on the water-filled tube.

When given a choice to drop sinking rubber objects or floating polystyrene objects, the crows opted for rubber 90 percent of the time.

However, they performed slightly less well when presented with a narrow tube and a wide tube of equal heights. The crows tended to opt to drop objects into the wide tube, which is less efficient although still effective.

Researchers say the birds' understanding of water displacement is comparable to that of a 5-year-old to 7-year-old child.

Also impressive is that the crows seemed to understand the difference in how hollow objects and solid objects affect water levels.

Although the birds failed at another challenge, scientists say their failure is still quite revealing.

In this task, there were three tubes. One held a floating cube of meat, one was connected to this first tube under the table, and the third tube was unconnected.

To complete the task and reap the meaty reward, the crows had to drop stones into the second tube to raise the water level in the connected tube that contained the treat. But the birds picked the connected tube and the unconnected tube an equal number of times.

Children are able to solve this problem around the age of 8.

However, the crows' failure to complete this task while being successful at the others hints that they were using causal understanding.

"They found the arbitrary task (dropping stones into an unconnected tube) counterintuitive," Amanda Seed, an expert on animal learning at the University of St. Andrews, told Reuters. This suggests "they formed a representation not only of what works, such as solid objects, but also why — that they displace the water level."

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