IT IS obvious to us that objects moved by a gentle wind must be light, and those not moved are heavy, but can animals work this out? It seems some crows can.
Sarah Jelbert at the University of Cambridge and her colleagues investigated by training 12 New Caledonian crows to discriminate between light and heavy objects. Six birds were rewarded when they dropped light objects into a food dispenser, and six were rewarded for choosing heavy objects. During this training, the birds were able to touch and pick up the objects.
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Then pairs of unfamiliar objects, one light and one heavy, were hung on strings in front of an electric fan before the birds could interact with them. After seeing how they moved in front of the fan, the birds touched the correct object first, according to the rule they learned earlier, in 73 per cent of tests. If the test was done with the fan off, the birds did no better than chance (Proceedings of the Royal Society B: Biological Sciences, ).
The breeze test may help crows when they forage for nuts, with weight indicating if a nut is good or rotten. An understanding of weight would also help any animal assess risk, such as the danger of objects falling on them. This test has never been done with any other animals, so it鈥檚 unclear how rare this ability is.