As the 2000-year-old story goes, the crow filled the bucket of water with stones until the level became high enough for him to quench his thirst.

Just a fable? Apparently not. Footage shows a rook - a relation of the crow - performing the feat to reach a worm floating on the water's surface.

The study, published by Current Biology, says that crows are innovative tool users, even though they are not known to use tools in the wild.

Footage of the experiments shows the rook first assessing the water level by peering at the tube from above and from the side, before picking up and dropping the stones into the water.

The birds were extremely accurate, using the exact number of stones needed to raise the worm to a height where they could reach it.