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

These new findings help explain why New Caledonian crows, which live on the remote tropical island of New Caledonia in the South Pacific, have evolved such remarkable tool-making abilities.

Going the extra mile allows these crafty creatures to get at hidden food several times faster than if they used basic (non-hooked) tools. Pictured are some of these elaborate hooks

Although crows are capable of extracting food with straight twigs, researchers found some of them actively manufacture hooked stick tools before going hunting

New Caledonian crows are the only species besides humans known to manufacture hooked tools in the wild. Birds produce these remarkable tools from the side branches of certain plants, carefully 'crafting' a crochet-like hook

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

THE BEST HOOK

Adult crows - which are expected to have the most tool-making experience - did not produce the deepest hooks and favoured the 'quick and dirty' technique.

Researchers believe experienced birds may not want to spend time making deep hooks as they also break more easily when inserted into small holes.

The depth of the hook was influenced by both the properties of the plant material, and the technique crows used for detaching branches.

When birds made controlled cuts with their sharp bills, the resulting hooks were significantly deeper than when they used a 'sloppier' alternative method of simply pulling off branches.

Careful cutting may leave more wooden material at the tip of the stick from which the hook can subsequently be 'sculpted'.

'In nature, getting food quickly means that birds have more time and energy for reproduction and steering clear of predators', said study co-author Professor Nick Colegrave from the University of Edinburgh's School of Biological Sciences.

'It's really exciting that we were able to measure the benefits of these nifty crow tools,' he said.

Scientists still don't know how crows acquire the 'know-how' and make hooks; they may inherit the ability from their parents, or learn by observing experienced birds.

Either way, because hooked-tool users will live longer and leave more offspring, the skill is expected to spread.

'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!' said Professor Rutz.

Last month researchers found adult crows, which are expected to have the most tool-making experience, did not produce the deepest hooks and favoured the 'quick and dirty' technique.

Depending on the task, they found that hooked tools were between two and ten times more efficient than non-hooked tools

Researchers believe experienced birds may not want to spend time making deep hooks as they also break more easily when inserted into small holes.

The study, also done by researchers from the University of St Andrews, reveals how crows manage to fashion particularly efficient tools, with well-defined 'deep' hooks.

'We suspected that tools with pronounced hooks are more efficient, and were able to confirm this in controlled experiments with wild-caught crows. The deeper the hook, the faster birds winkled bait from holes in wooden logs', said Professor Rutz.

According to the researchers, making very deep hooks may not be the best strategy in the wild.

Scientists still don't know how crows acquire the 'know-how' and make hooks; they may inherit the ability from their parents, or learn by observing experienced birds

Last month researchers found adult crows, which are expected to have the most tool-making experience, did not produce the deepest hooks and favoured the 'quick and dirty' technique

Professor Rutz said: 'It probably takes more time and effort to make such tools, and experienced birds may try to avoid these costs. It is also possible that deep hooks break more easily when inserted into narrow holes and crevices.'

Scientists found crows visualised the task before starting in a similar way to how humans would.

The depth of the hook was influenced by both the properties of the plant material, and the technique crows used for detaching branches.

When birds made controlled cuts with their sharp bills, the resulting hooks were significantly deeper than when they used a 'sloppier' alternative method of simply pulling off branches.

Careful cutting may leave more wooden material at the tip of the stick from which the hook can subsequently be 'sculpted'.

CROWS AS SMART AS CHILDREN

Crows have a reasoning ability rivalling that of a human seven-year-old, research has shown.

Scientists came to the conclusion after subjecting six wild New Caledonian crows to a battery of tests designed to challenge their understanding of cause and effect.

The tasks were all variations of the Aesop's fable, in which a thirsty crow drops stones to raise the level of water in a pitcher.

In the 'water displacement task', crows worked out how to catch floating food rewards by dropping heavy objects into water-filled tubes.

They demonstrated an ability to drop sinking rather than floating objects, solid rather than hollow objects, to choose a high water level tube over one with low water level, and a water-filled tube over one filled with sand.

The birds' understanding of the effects of volume displacement matched that of human children aged between five and seven, scientists from the University of Auckland claimed.