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New Caledonian crows, well known for wielding tools such as sticks, prefer to hold a tool on the left or the right sides of their beaks, in much the same way that people are leftor right-handed. Now researchers reporting in the Cell Press journal Current Biology suggest that those bill preferences enable each bird to keep the tip of its tool in view of the eye on the opposite side of its head. Crows aren't so much leftor right-beaked as they are leftor right-eyed. 'If you were holding a brush in your mouth and one of your eyes [was] better than the other at brush length, you would hold the brush so that its tip fell in view of the better eye,' said Professor Alex Kacelnik of Oxford University's Department of Zoology, an author of the report. 'This is what the crows do.' The new study also suggests that the birds'' extreme binocular vision - characterised by an unusually wide field of view in comparison to other species - actually helps the crows see better with one eye at a time. 'Binocular vision is often connected to allowing the brain to compare the images seen by each eye, inferring properties of the scene from the differences between these images,' said Antone Martinho of Oxford University's Department of Zoology, first author of the report. 'We thought that their binocular fields would facilitate binocular vision, perhaps allowing the birds to judge the distance from tool tip to target.