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Crows show the right stuff

Natural History, March, 2002 by Kirsten L. Weir

CROWS SHOW THE RIGHT STUFF The recent discovery of a right-side visual preference in a species of crow has challenged the belief that we're the only creature with a predictable--and overwhelming--bent for taking one side. Certain populations of parrots favor a particular foot when manipulating their food, and some wild chimpanzees favor a particular hand, but this crow and humans are the only known examples of entire species with a right-sided preference in manipulatory tasks.

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With its beak, the New Caledonian crow (Corvus moneduloides), a native of the South Pacific island of Grande Terre, the main island of New Caledonia, constructs toots from leaves of the pandanus tree, using them to pluck insects from rainforest vegetation. This corvine do-it-yourselfer sometimes fashions the tool from the left edge of a leaf and sometimes from the right. An unmistakable mark--known as a counterpart--remains on the leaf edge, recording the crow's choice of working direction. When cutting a tool from a leaf's left edge, the crow turns the right side of its head (and its right eye) toward the leaf, and vice versa when it cuts the leaf's right edge.

Psychologists Gavin R. Hunt and colleagues at the University of Auckland in New Zealand collected more than 3,700 of these counterparts on Grande Terre. They found that all across the island, crows preferred to make tools from left leaf edges, even when the leaves grew in a direction that would have made it easier to work at the right. Working at the left edge allows a crow to keep its right eye on the complex task at hand.

Previously scientists suggested that human right-handedness might be a consequence of the evolution of Language, since language and right-handedness are both predominantly controlled by the left side of our brain. But the new finding supports the idea that right-handedness in a species is an adaptation for the efficient programming of complex sequential processes--including language and the construction of crow tools. ("Laterality in Tool Manufacture by Crows," Nature 414, 2001)

Crows show the right stuff

Natural History, March, 2002 by Kirsten L. Weir

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