When it comes to making tools, crows on the Pacific island of New Caledonia are mostly right-handed--or perhaps "right-billed" is the term. Researchers studying how these birds fashion tools for foraging have found that most of them prefer using their right eye and the left part of their brain--just like most humans do.
The vast majority of humans use their right hands for tasks demanding strength or precision. Only recently have researchers started to discover consistent handedness, or laterality, in many other creatures--from chimps and toads to chicks and pigeons. Last year, ecologist Gavin Hunt of the University of Auckland in New Zealand was the first to show that handedness also plays a role in animal toolmaking. Hunt studied New Caledonian crows, a species that snips carefully tapered strips off leaves from the pandanus tree and uses them to retrieve beetle grubs from crevices. Some crows tend to snip tools from the left sides of leaves, using their right eye to guide their behavior, while others prefer to work from the other side, Hunt found.
Now, for a more quantitative analysis, Hunt and two colleagues have gone back to New Caledonia and studied some 3700 leaf strips and outlines of tools cut from leaves. They found that two-thirds of the tools were cut from the left sides of leaves--indicating a clear lateral preference, the team says. This was true across the entire island, suggesting laterality is hardwired in the birds' brains and not a product of local social traditions or environmental pressures, the researchers say. The birds' right eye is connected to the left side of their brain; apparently, says Hunt, their left hemisphere is better at controlling complex sequential tasks, just as it is in humans.
The study shatters the widely held myth that tool use and laterality are connected only in humans, say behavioral scientists. And although there's already "a battery of evidence" for laterality in animals from lab studies, Lesley Rogers of the University of New England in Armidale, Australia, says, "we're only beginning to look at how this laterality manifests itself in the wild."