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Crows are known for their above-birdbrain intelligence, and New Caledonian crows have been observed using tools in their day-to-day lives. Other members of the crow family, however—such as rooks—don't seem to have this tool-using tendency in their natural habitats. But researchers at U.K. universities Cambridge and Queen Mary have shown that in a lab setting, hand-raised rooks quickly began using tools when faced with a challenge.
The findings, published earlier this week in Proceedings of the National Academy of Sciences, point to the notion that when food is plentiful, the birds can flourish without tools. In instances of controlled scarcity, however, they were perfectly able to start using—and even creating—tools.
"They rival habitual tool users such as chimpanzees…when tested in captivity," lead study author and graduate researcher Chris Bird said in a statement. Chimpanzees have been known to use modified sticks to fish out termites—and even stab small primates known as bush babies—for lunch.
The birds started using stones that researchers left in the aviary to tip a platform inside a tube, which released a tasty worm. When left without stones in a testing cage, each of the birds fetched one to use from a connected outdoor run. When they were given a sick instead, the birds chose to use that to the same end. And when the stick was too light to make the platform collapse by dropping it, the birds used it to push down into the tube and get the job done.
The rooks also engaged in "metatool" use, which means using one tool to enable the use of another—in this case, a large stone (too large to fit in the tube) could be used to access either another large stone (also too big) or a small stone. All of the birds used the big stone to get the little stone on the first try.
Finally, although the birds weren't observed making any drills or lathes, they did modify and create tools to get worms. When given a stick with side branches that wouldn't fit into the tube, the birds efficiently snapped off the pesky pieces so that it could be inserted smoothly. They were also able to use wire hooks to lift a food bucket out of a clear tube—and make a hook out of a straight wire (see a video here), a talent that had only ever been demonstrated by one New Caledonian crow.
Other species that have been known to use tools include chimpanzees, orangutans, capuchin monkeys, sea otters, Egyptian vultures, herons, woodpecker finches and, of course, humans.
Image of a rook using a hook to get food out of a tube courtesy of Chris Bird/University of Cambridge