Stone the crows! Crafty birds make hooks from twigs to dig out fast food, scientists say

They are the craftiest of crows, known for their ability to adapt twigs into tools to help them eke out tasty morsels.

Now biologists have revealed why New Caledonian crows go to such an extent to craft the bespoke hooks: for their love of “fast food”.

Researchers from St Andrews and Edinburgh universities found that the adapted twigs were several times faster than straight twigs at enabling the crows to catch their prey.

Professor Nick Colegrave, from Edinburgh, said: “Getting food quickly means that birds have more time and energy for reproduction and steering clear of predators. It’s really exciting that we were able to measure the benefits of these nifty crow tools.”

The crows, which live on the island of New Caledonia in the South Pacific, are famous for using tools to winkle beetle grubs and other small prey out of hiding places. Lead author Dr James St Clair, from St Andrews, said: “It’s a painstaking sequence of behaviours. 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.”

Biologists have long assumed there was some benefit to crows manufacturing hooked tools but had no idea how great that may be. The team conducted experiments to record how long the crows, which were caught and later returned to the wild, took to extract food in a range of naturalistic tasks, using either hooked or non-hooked tools.

Depending on the task, they found that hooked tools were between two and 10 times more efficient. Project leader Professor Christian Rutz, from St Andrews, said: “Our results highlight that even relatively small changes to tool designs can significantly boost foraging performance.”

What remains unknown is how the crows acquire their tool-making skills. They could be inherited or developed from watching other birds.

Professor Rutz said: “We’ve all heard that the early bird gets the worm. In the case of the New Caledonian crow, it’s the skilled hook-maker that gets the worm, or at least it gets many more worms than its less-crafty neighbours.”@RossLydall