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Auckland - Crows with a knack for making tools have surprised scientists by showing themselves to be left-handed, a sign of intelligence never seen before at a species level outside humans.
The New Caledonian crow, Corvus Moneduloides, displays a clear left preference when manufacturing tools from leaves which they use to catch insects. The crows are skilful tool makers, cutting a stepped taper from the tough leaf of the pandanus tree which is wide at one end and thin at the other.
They use these implements to extract insects out of inaccessible crevices. Gavin Hunt and colleagues from the University of Auckland, New Zealand, found that the birds consistently made the tools working from the left side of the leaf.
This was discovered by looking at 3.727 torn edges of leaves from which insect-catching tools had been cut. The leaves were taken from 733 pandanus trees at 19 sites scattered throughout the mainland island of Grand Terre, New Caledonia.
Even when leaves spiralled anti-clockwise, providing easier access to right edges, the crows still worked from the left. Writing in the journal Nature, the scientists point out that the regular shape of the tools is mostly determined by the crows themselves, rather than the nature of the leaf material. This implied a high level of neural processing in the brain.
Right-handedness in humans has been thought to be the result of the evolution of language, said the scientists. But the study indicated a more general possibility, that at the species level it is an adaptation for the efficient neural programming of complex sequential processing, of which language and right-handedness in humans, and stepped tool manufacture in crows, are examples.
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