Researchers in New Zealand have found that crows on the South Pacific
island of New Caledonia display right-"handedness" (right bias) when
making their tools—a trait that was thought to be unique to
humans.
The New Caledonia crows (Corvus moneduloides) make
tapered serrated tools from leaves, and use these tools to prod and
extract grubs and insects from holes and crevices. The tools are made
from either the right or left edge of leaves from the pandanus tree.
By studying the leaves from which tools were cut, the researchers determined that the crows on the island had a preference for making tools from the left edge of a leaf—a process that favors use of the right eye and right side of the beak.
This suggests that the crows are "righties," or "right-biased," and that the left side of their brains might be specialized for tool-making, said biologist Gavin Hunt of the University of Auckland in New Zealand, who led the research.
Hunt and colleagues examined almost 4,000 crow artifacts from 19 sites along the narrow Grand Terre Island of New Caledonia, the only region where crows are known to make leaf tools. He found that the majority of crows preferred using the left side of the leaf.
"What is nifty about Gavin's study is it tells us we [humans] are not unique, we are not the only species with a right bias," said behavioral ecologist William McGrew of Miami University in Oxford, Ohio.
"Right" Dominance
In every society that has been studied, the majority of people are right-biased, said McGrew. About 90 percent of all people, for example, write with their right hands.
McGrew studies handedness in wild chimpanzees. "We watch every single movement the chimps make with their hands—grooming, eating, tool-making, for example—and have found that chimps only demonstrate a right or left bias when it comes to tool use," said McGrew. "For all other activities, they use both hands equally," he noted.
Half of all chimpanzees are lefties and the other half favor the use of the right hand when using tools, McGrew said. There is not a species-wide preference as there is with humans and New Caledonia crows.
It has been suggested that in humans, the species-wide right bias is linked with the development of language, which is also controlled by the left side of the brain. "But with Hunt's study, we now have an example where a right bias is clearly not linked to language," said McGrew.
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