# Chicks do arithmetic

Recently hatched fowls appear to add and subtract

Count your chickens after they hatch, and they may do a little arithmetic 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 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 March 31 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 numerical skills in human babies, points out 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.

To invent math tests for young chickens, the researchers took advantage of the chicks’ tendency to cluster. Solo chicks typically rush over to join the largest group of their companions in the neighborhood. Researchers put sets of little plastic balls or bits of colored paper into the cage with a recently hatched chick. “They treat the balls as companions,” Rugani says. At test time, chicks scurry over to the larger group of their ball or paper pals.

In early, simple tests, researchers found that chicks discriminate between sets of two and three objects. It’s the number three that lures them, not the outline or the total bulk, Rugani says. For example, when researchers let chicks choose between three little pieces of red paper or the same area of paper divided into just two parts, chicks mostly preferred three pieces.

For the toughest set of tests, each chick watched as a researcher first hid objects behind each of two screens. Then the tester let the chick see some of the objects being moved from behind one screen to the other. To go to the screen with the larger number, the chick had to keep track of addition and subtraction.

About 75 percent of the time, chicks did it right. For example, researchers put four balls behind one screen and two behind another, and then shifted two of the original four to the pile behind the second screen. Most of the chicks weren’t fooled by that original big flock of four balls. When released to make their choice, most chicks scuttled over to the second screen, which had started with a puny two and now had four.

“The chick study is powerful because it shows that an animal can use a sense of numbers and basic math with almost no experience on Earth,” says Jessica Cantlon of Duke University in Durham, N.C., who studies numerical powers in primates. The study, she says, “shows that animals might be evolutionarily endowed with an ability to track and manipulate numbers, rather than picking up their numerical abilities gradually over development.”