New Caledonian crows can remember what a tool looks like and then make a new one just from memory. The skill to make a mental image of something and then recreate it in this way is something usually only seen in humans.
These crows are known to make a wide range of tools, including hooked and barbed sticks. But, until now, it wasn’t clear how certain tool designs were passed through generations, as the crows did not seem to just imitate other crows. of the University of Cambridge, UK, and her team wanted to see if the crows were able to remember effective tool designs and recreate them.
The team trained eight wild crows by initially offering them a choice between two small and two larger pre-fabricated cardboard vouchers. The cardboard vouchers released a reward – some meat – when they slid it with their beaks into the slot of a dispenser. Half the birds were taught that the larger vouchers earned the rewards, and half learned that the smaller vouchers worked.
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When Jelbert offered the birds an oversized card that wouldn’t fit through the slot, the birds gripped it with their claws and ripped it into shape with their beaks to the size that had most recently worked for them—either the smaller vouchers or the slightly larger ones. “The only way they could do this was by memorising what the ideal shape should be,” says Jelbert.
Rather than copying how other crows make tools, they learned by focusing on the tool itself. They recognised its usefulness, remembered what it looked like and worked out how to make it anew. This might explain how the tools become increasingly complex over time as crows hold a mental image of the right tool and then make slight changes, which are then picked up by future generations.
“They are performing a new behaviour,” she says. “They’ve transferred experience of what works for them into a combination of memory and manufacturing ability.”
“This work is a remarkable step towards confirming that these birds exhibit a kind of cumulative cultural evolution that has rarely if ever been demonstrated in non-human animals,” says Stephen Nowicki of Duke University in Durham, North Carolina.
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