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Complex tools help crows hunt more quickly

Scientists have discovered why some crows craft elaborate hooked tools from branched twigs.

The birds’ creation of hooked twigs to extract prey enables them to get at hidden food several times faster than using simple, unmodified sticks.

Foraging aids

Caledonian crow with a curved stick. Credit James St Clair
Caledonian crow with a curved stick. Credit James St Clair

Biologists at the Universities of Edinburgh and St Andrews studied New Caledonian crows, which are famous for their use of tools to winkle beetle grubs and other small prey out of hiding places.

Although crows are capable of extracting food with straight twigs, in some areas they actively manufacture hooked stick tools before going hunting.

Crows create tools in a painstaking sequence of behaviours.

They seek out particular plant species, harvest a forked twig, and then, while firmly holding it underfoot, they carve, nibble and peel its tip, until it has a neat little hook.

Biologists had long assumed that there was some benefit to crows manufacturing hooked tools, but had no idea just how much better they might be.

Time-saving tools

The team conducted experiments on the island of New Caledonia in the South Pacific 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 to ten times more efficient than non-hooked tools.

It is not known how crows acquire the ability to make hooks.

They may inherit the ability or learn by observing experienced birds.

Birds that use hooked tools tend to live longer and leave more offspring.

The study is published in Nature Ecology & Evolution.

In nature, 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.

Professor Nick Colegravechool of Biological Sciences, University of Edinburgh

Our results highlight that even relatively small changes to tool designs can significantly boost foraging performance.

Professor Christian RutzUniversity of St Andrews