Already famous for their impressive problem solving skills, New Caledonian crows can now add logical inference to their repertoire. Alex Taylor of the University of Auckland in New Zealand placed a box with food near a hanging blue sheet, behind which someone could hide. A stick protruded from the sheet. Crows watched as people walked behind the sheet, then saw the stick move, and finally saw the people leave.

This seemed to make sense to them. But if they saw the stick and box move without observing someone enter and exit the hideaway, the crows became more cautious, exploring the blue sheet instead of probing the box for food. (See a video of this behavior at ScienceNOW.) According to the researchers, the crows had likely inferred that if the stick was capable of moving, and no human left, maybe it could still move.

“We show that tool-making New...


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