Crafty Crows Found to Be "Right-Handed"

Bijal P. Trivedi
National Geographic Today
December 12, 2001
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

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.

The results of Hunt's study are published in the December 13 issue of the journal Nature.

Food "Cost-Benefit Analysis"

In another study of crows, researchers have found that Northwestern crows (Corvus caurinus) in the United States constantly scan their surroundings for opportunities to steal food from other birds.

Most animals and birds, when in groups, tend to be less vigilant and spend more time eating. That is not the case with Northwestern crows.

Animal behavior specialists have long thought that the crows, when they scan their surroundings, are on the lookout for predators. But the new study reveals that the birds are shrewdly watching other crows for opportunities to steal food.

Renee Robinette Ha and James Ha, both of the University of Washington in Seattle, have found that Northwestern crows perform a "cost-benefit analysis" before deciding what food to steal from another member of the flock.

"They don't steal just any type of food," said Robinette Ha. "They only steal food that requires a long handling time, like crabs or clams, or foods that are high in energy."

Crabs and clams require time and energy to break open and access the meat. Crows drop clams on rocks to smash them open. This attracts the attention of other birds, which hover waiting to snatch a free morsel.

Sand lances, silvery fish the size of sardines that burrow into sand at low tide, are another popular target of marauding crows, said Robinette Ha.

Sand lances are difficult to find. Researchers are not sure whether the crows can hear them or feel vibrations as the fish burrow. But once a crow begins to dig, other crows form a circle around the digger, waiting in ambush. As soon as the fish is pulled out of the sand, the other crows try to snatch it away.

The crows don't attempt to steal fast food such as bugs and worms.

"These birds are tremendously clever," said Robinette Ha. "They are adapable and have complex social life and interactions, which makes them challenging to study."

This study was published in a recent issue of the journal Animal Behaviour.

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