Scientists have discovered why some crows craft elaborate hooked tools out of branched twigs.
Biologists found crows going the extra mile to use crafty tools were able to get at hidden food several times faster than those using basic, unmodified sticks.
New Caledonian crows are famous for their use of tools to winkle out beetle grubs and other small prey from hiding places.
And although crows can extract food with straight twigs, in some areas they manufacture hooked stick tools before going hunting.
“It’s a painstaking sequence of behaviours,” said lead author of the study Dr James St Clair, of the School of Biology, St Andrews University.
“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.”
Scientists have long assumed that there was some benefit to crows manufacturing hooked tools, but had no idea just how much better they might be.
Biologists at the universities of St Andrews and Edinburgh carried out experiments to record how long wild-caught crows took to extract food 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.
Project leader, Professor Christian Rutz from St Andrews University, said: “That’s a huge difference.
“Our results highlight that even relatively small changes to tool designs can significantly boost foraging performance.”
These findings help explain why New Caledonian crows have evolved such remarkable tool-making abilities.
Professor Nick Colegrave from Edinburgh University’s School of Biological Sciences added: “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.”
But scientists still don’t understand how crows acquire the ‘know-how’ to make hooks.
It is thought they may inherit the ability from their parents, or learn by observing experienced birds.
The skill is expected to spread as hooked-tool users will live longer and leave more offspring.
The study appears in Nature Ecology & Evolution.
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