Animal behaviour: Laterality in tool manufacture by crows.

New Caledonian crows (Fig. 1) fashion tapered tools from either the left or the right edge of the long narrow leaves of pandanus trees or screw pines, which they use to extract invertebrates in rainforest vegetation. Although right-handedness is thought to be uniquely human, we show here that crows from different localities display a widespread laterality in making their tools, indicating that this behaviour is unlikely to be attributable to local social traditions or ecological factors. To our knowledge, this is the first demonstration of species-level laterality in manipulatory skills outside humans.