August 10, 2009

When researchers presented crows with a challenge modeled after Aesop’s fable The Crow and the Pitcher, the birds were able to figure out how to raise the water level by dropping stones into the glass – just like in the fable (see video below). Amazingly, the crows also selectively chose large pebbles over small ones, and quickly realized that dropping rocks into a container of sawdust didn’t have the same effect.

In a study published Thursday in Current Biology, the researchers noted that the results provided evidence that rooks are capable of the remarkable problem-solving ability described more than two thousand years ago in Aesop’s fable.

The researchers took four adult rooks, a type of intelligent crow, and tempted them with a worm floating just out of reach, on top of the water. Then they placed a pile of small rocks next to the glass. After assessing the height of the water in the glass, the crows raised the water level by dropping stones into the glass.

After capturing the worm, the birds stopped putting stones into the water, and they didn’t try to grab the worm until they’d dropped in a certain number of stones. Researchers concluded that the rooks assessed the starting level of the water, and estimated the number of stones necessary to raise the level before starting the work.

Before this experiment, the birds had never been exposed to a glass with water in it, and they’d never used stones as tools. According to the researchers, the only other animal known to perform this kind of task is the orangutan, which has been recorded spitting into a tube to bring a peanut into reach.