Hatchlings may add, subtract: results point to built-in numerical understanding.

Forget counting your chickens. They may do it themselves. Chicks only 3 or 4 days old manage an animal version of adding and subtracting, says Rosa Rugani of the University of Trento Center for Mind/ Brain Sciences in Rovereto, Italy.

Inspired by experiments with human babies, Rugani and her colleagues worked out tests based on adding objects to and taking them away from little piles hidden behind screens. With no special math coaching, the chicks did a decent job of keeping track of object shifts representing such problems as 4--2 = 2 and 1 + 2 = 3, she and her colleagues report online April 1 in Proceedings of the Royal Society B.

"This is the first demonstration of adding and subtracting in young animals" other than humans, Rugani says. Other animals, including some primates and dogs, have demonstrated numerical powers as adults.

Karen Wynn of Yale University, who has reported evidence of basic numerical skills in human babies, says that the chicks haven't had a chance to learn or develop much. "This work, then, is a compelling existence proof that numerical understanding comprises a built-in system of unlearned knowledge," Wynn says.

Chicks tend to cluster, even with experimental "chicks" that are actually familiar little plastic balls. In one test, each chick watched as a researcher first hid balls behind each of two screens. Then the tester let the chick see some of the balls being moved from one screen to the other. To go to the screen with the larger number, the chick had to keep track of addition and subtraction.

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About 75 percent of the time, chicks did it right, scuttling to the screen that ended up with the most balls.