As users—and even occasional makers—of tools, rooks in captivity have been documented bending wire and dropping rocks to access treats put just out of their reach by researchers. Most recently, a team at the University of Cambridge has discovered some truth to one of Aesop’s fables, "The Crow and the Pitcher," in which a thirsty crow drops rocks into a pitcher to raise the water level so he can reach it.

Trading water for a worm, researchers observed rooks—avian cousins of New Caledonian crows, which use tools in the wild—doing just the same thing in a lab experiment. The findings were published today in Current Biology.

When presented with a desirable worm floating out of reach in a narrow tube, a rook used stones to raise the water level to bring the worm high enough to nab. The bird also seemed to quickly figure out how many and what size rocks work best to raise the floating worm to where it could be reached. A final test, in which researchers presented a rook with one water-filled tube and one sawdust-filled tube, showed that the bird understood the sawdust wouldn't rise like water, as it only put rocks in the water tube.

"Corvids are remarkably intelligent, and in many ways rival the great apes in their physical intelligence and ability to solve problems," Chris Bird, lead study author at Cambridge, said in a prepared statement.

Image courtesy of Chris Bird