Crafting hooked tools let crows extract grubs hidden in crevices more quickly than using a straight twig. (J.St Clair)
Crafting hooked tools let crows extract grubs hidden in crevices more quickly than using a straight twig. (J.St Clair)

WASHINGTON - Some New Caledonian crows craft hooked tools out of branched twigs, and Scottish biologists have discovered why - the birds can extract food from cracks and crevises several times faster than by using straight twigs.

"It is a painstaking sequence of behaviors,” explains Professor James St. Clair, from the University of St. Andrews, the lead author of the new study in the current issue of Nature Ecology & Evolution.  “Crows seek out particular plant species, harvest a forked twig, and then, firmly holding it underfoot, carve, nibble and peel its tip, until it has a neat little hook.”

Watch a New Caledonian crow make and use a hooked tool (Credit Rutz Group)

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The Scottish team conducted experiments to record how long wild-caught crows took to extract food from a range of naturalistic tasks, using either hooked or non-hooked tool designs.  Depending on the task, they found that hooked tools were between two and 10 times more efficient than non-hooked tools.

Although it takes the crow a while to create the hook, getting food more quickly means it has more time and energy for reproduction and avoiding predators.  The researchers do not know whether the hook-making know-how is inherited or learned by observation, but because hooked-tool users will live longer and leave more offspring, the skill is expected to spread.