By BBC News Online's Ivan Noble

A clever species of crow is causing scientists to puzzle over how most human beings came to be right-handed.

It's quite a fine manipulation to cut and rip the shapes out of the leaves

Gavin Hunt University of Auckland

The bird rips pieces from leaves and turns them into tools for removing insects from trees.

But when it does, more often than not it prefers to use the right side of its beak.

This preference for one side of the body over another is more commonly seen in humans, gorillas and chimps, and its discovery in a bird species raises the question of how it developed.

Outdoing chimpanzees

Gavin Hunt of the University of Auckland, New Zealand, says that the birds' toolmaking is quite skilful.

The "right-beakedness" was statistically significant Image: Gavin Hunt

"It's quite a fine manipulation to cut and rip the shapes out of the leaves," he told BBC News Online. "It's a unique system that any animal fashions tools to this extent. Even chimpanzees don't."

He and his colleagues describe in the journal Nature how they collected the remains of leaves cut up by Corvus moneduloides, a crow species from the French overseas territory of New Caledonia in the southwestern Pacific Ocean.

The scientists worked out from the leaves' shape and structure how they must have been used.

'Right-beakedness'

Statistical analysis showed that the birds had a definite preference for using the right side of their beaks, albeit not as highly defined a preference as in humans.

Some researchers have suggested that the tendency towards right-handedness in humans is a result of the ability to speak, a mental activity concentrated in the half of the brain which controls the body's right side.

The discovery of "right-beakedness" in crows makes it look more likely that handedness has a more general origin.

Turning a leaf into an effective insect-winkling tool requires a considerable degree of brain effort.

Efficient brains

Dr Hunt and his colleagues say their results point towards handedness being a product of being able to carry out complex sequences of actions.

Those sequences of actions could result in the making of a tool or the production of speech.

Either way, concentrating all the brain effort in one side of the brain seems to be more efficient.

Laterality, the preference for one side over another, seems to be a byproduct of this efficiency.