Tool use in rooks

Rooks have a remarkable aptitude for using tools.

Tests on captive birds have revealed that they can craft and employ tools in a number of different ways to solve a variety of different problems . The findings came as a surprise as rooks are not known to use tools in the wild. Despite this, the UK team said the birds' skills rivalled those of well-known tool users such as chimpanzees and New Caledonian crows. Dr Nathan Emery from Queen Mary, University of London, said: "The study shows the creativity and insight that rooks have when they solve problems."

The scientists focused on four captive rooks: Cook, Fry, Connelly and Monroe. In one test, the birds were presented with a vertical tube, running down to a trap-door with an out-of-reach worm perched upon it, as well as a number of different-sized stones placed nearby.  The scientists discovered that the rooks would select the largest stone, which was heavy enough to push open the trap-door, and drop it into the tube to release the snack. And when given a selection of different-shaped stones, some of which could fit into the tube, some of which could not, the rooks opted for a tool that would give them access to the treat.

Lead author Christopher Bird, from Cambridge University, said: "We have found that they can select the appropriate tools out of a choice of tools and they show flexibility in the types of tools they use."

The researchers also found the rooks could use two tools in succession - something that is described as metatool use. They gave the birds a large stone, as well as two vertical tubes, one wide, with a small stone perched at the bottom on a trap-door, and another thin, this time containing a worm. They found that the rooks would first drop the large stone into the wide tube to release the smaller stone, and subsequently drop this small stone into the thin tube to free the tasty treat. Until then, the use of more than one tool in sequence had only been seen in great apes and New Caledonian crows.

Rooks have also repeated Aesop's fable, by working out that dropping stones into water will raise its height, giving them access to some floating food.

Perhaps most surprisingly, the team also revealed that rooks could modify and create new tools. They found that the rooks would bend a piece of straight wire into a hook so that they could retrieve a bucket laden with food from the bottom of the vertical well. Until then, this novel tool-fashioning behaviour had only been reported for a single New Caledonian crow called Betty. But in this study, three of the four rooks created the hook in their first trial.

Mr Bird said: "It was a big surprise to find out that rooks could use tools. We've seen this kind of tool use in New Caledonian crows, but the interesting thing about the rooks is that they do not use tools in the wild. Because they don't use tools in the wild, the question is why should they have evolved the ability to use tools in the lab and understand the properties of those objects as tools? "Is this a form of general intelligence that has been co-opted for tool use?"

The researchers say the finding raises the possibility that other corvid species may also possess an innate ability to use tools.