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New Caledonian crow with a tool it crafted

The New Caledonian crow—shown here with a tool it crafted—is capable of high-level cognition, researchers report.

Behavioural Ecology Research Group, Oxford

Clever Crows, Complex Cognition?

Called “feathered apes” for their simianlike smarts, crows use tools, understand physics, and recognize themselves and humans. But new research suggests that the brainy birds may be even smarter than was previously thought. Given a complex problem and an assortment of tools, New Caledonian crows came up with a creative solution that hints at higher-order thinking.

A native of New Caledonia and the Loyalty Islands in the Pacific Ocean, the New Caledonian crow makes tools from sticks or leaves and uses these to draw tasty grubs from hollows in trees. That in itself wouldn’t be so impressive—even some insects use tools this way—but the crows also combine tools when they needed to. In a 2007 experiment conducted by graduate student Alex Taylor and colleagues at the University of Auckland in New Zealand, the crows used a shorter stick to grab another that was long enough to get food outside their reach.

This kind of action seems to indicate insight or reasoning. But not everyone was convinced, says Taylor. “Some scientists suggested the tools became valuable in themselves because they were associated with food,” he says. That would mean the birds sought each stick because they wanted it, not because they understood the stick’s potential function. The distinction, although subtle, marks the difference between high- and low-level learning, and it speaks to a central question of cognition research: How do you determine whether an animal is thinking through its actions, or simply learning through association a series of behaviors and combining them?

So Taylor trained seven wild crows to associate a short stick with ineffectiveness; the crows failed to obtain their out-of-reach food with the stick and eventually began to ignore or reject it. Then they were divided into two groups, an innovation group and a training group. The training group learned six activities—such as how to use a short stick to extract a long stick from a toolbox—that together could help them get meat with long and short tools. The innovation group wasn’t taught how to use a short stick to extract a long stick from the toolbox, but did learn other techniques.

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Brainy bird. New Caledonian crow Sam combines tools to solve a complex problem on her first try.
Credit: Alex Taylor

When tasked with reaching a snack in a hole using a short stick on a string and a longer stick trapped in a toolbox, all of the crows pulled it off. The three birds in the training group linked the behaviors they had learned into a new behavior. They freed the short stick from the string, used it to dislodge the long stick, and used the long stick to obtain their food. And all four crows in the innovation group figured out the sequence on their own. One crow in the innovation group stared at the setup for less than 2 minutes and then performed the whole trial correctly on her very first attempt.

The results, published tomorrow in the Proceedings of the Royal Society B, confirm Taylor’s previous finding, but with a new twist. The crows’ willingness to use the short stick despite its intrinsic unattractiveness (its inability to get food on its own) makes a stronger case for higher-level cognition, says Taylor. It shows that pleasant associations (stick = food) aren’t driving the behavior.

The study is “ingenious” and reflects a positive trend toward studying how animals might think and not just what they do, says Alex Kacelnik, a zoologist at the University of Oxford in the United Kingdom. The study may not definitively rule out associative learning—the wild crows already had considerable experience with sticks of all sizes by the time they took Taylor’s test, Kacelnik notes—but it comes close, he says. “These animals learn something interesting, no doubt,” he says, “and can use it flexibly to generate new behavior, a feat that until a couple of decades ago was thought to be restricted to humans and other apes.”