A tool-using strategy that was key to the advancement of early humans has been observed by scientists in a bird. "Metatool use", the ability to use one tool on another, is something that humans and great apes such as chimps and orang-utans are capable of, but with which monkeys struggle.

However, a study has shown that New Caledonian crows can manage this task easily. Researchers offered the crows a tasty morsel of meat that was out of reach in a box. To reach the food the birds had to use a long stick. But this stick was inaccessible in another box. To reach the long stick, the birds had to prise it out with a smaller stick which they could reach.

"It was surprising to find that these creatures performed at the same levels as the best performances by great apes on such a difficult problem," said Russell Gray, of the University of Auckland, New Zealand. "Six out of seven birds tried to get the long stick with the short stick at their first attempt at solving the problem."

The test revealed that the birds knew the short stick was too small to reach the food but that the longer stick would solve the problem. "They had to inhibit their normal response of trying to get the food directly with the short stick and realise that they could use the short stick to get the long stick," he said. New Caledonian crows previously have been shown to adapt tools for a specific job, something only a few primates can manage. Chimpanzees are the most adept ape tool-users apart from humans, using spears to hunt bushbabies, rocks to crack nuts and sticks to fish for termites.

Metatool use, involving making more complex and useful tools, was vital in our ancestors' development, say the researchers. "[It] may reflect the 'cognitive leap' that initiated technological evolution," they write in the journal Current Biology.

The ability is conceptually hard, they argue, because the applying of one tool to another represents another step removed from the goal itself . First the animal has to realise that tools can be used on non-food objects, second it has to suppress the urge to go straight for the food itself, and third, it has to perform a sequence of actions in the correct order.

And, to see the solution to the problem, requires "analogical reasoning", the ability to see a new situation as essentially similar to a previous one.

To ensure the birds were not simply probing randomly with the short stick and getting the long stick by trial and error, the test involved yet another box with a stone inside. Only one bird tried poking the short stick into this box - and that was after she had already solved the problem.