Researchers have found that pigeons can learn abstract numerical rules, like the ability to discriminate between quantities of items. (Snap Decision/GETTY IMAGES)

Pigeons can learn abstract numerical rules, a skill that scientists had believed only primates possessed, researchers say.

And they believe the birds’ ability to reason numerically is probably something that a wide variety of species have.

Many species can discriminate between quantities of items, sounds or smells. But only primates (all species, from lemurs to chimpanzees) were known to be able to reason numerically.

For example, scientists showed in 1998 that rhesus monkeys can grasp the concept of “ordinal number.” That is, given two sets containing from one to nine objects, they can determine that, say, a set with one thing should be placed before a set with two things, and so on. Since then, “there have been nice, consistent findings of this ability across all primate species,” says Damian Scarf, a comparative psychologist at the University of Otago in Dunedin, New Zealand, and lead author of the new pigeon study. “But it’s always been a question if this is unique to primates.”

To find out, Scarf and his colleagues gave a test to three pigeons.

Scarf spent a year training the pigeons to order three sets containing one to three objects, such as a set of one yellow rectangle, two red ovals and three yellow bars. The sets would appear on a computer screen, with colors and shapes changing each time. The birds had to peck at them in the ascending numerical order to get a food reward. “They had to learn that it was the number of items that mattered, not the color or shape,” says Scarf.

The pigeons were then asked to place two sets containing between one and nine items in the correct, ascending sequence to see if they understood the basic principle behind ordinal numbers. In their training sessions, the birds had learned only first, second and third. But they didn’t falter when presented with new numbers of shapes, such as five ovals or seven rectangles. The pigeons’ scores were far better than chance responses would have yielded, says Scarf.

“I thought it was amazing that monkeys could do this, so we should be even more impressed that pigeons can, too,” says Elizabeth Brannon, a cognitive neuroscientist at Duke University in Durham, N.C., and lead author on the original rhesus monkey study. The disparate creatures may be relying on the same neural mechanism to perform the task, she speculates. “These new findings suggest that, despite completely different brain organization and hundreds of millions of years of evolutionary divergence, pigeons and monkeys solve this problem in a similar way,” says Brannon.

Scarf and his co-authors suggest that other species may demonstrate similar skills. Colleagues agree. “The ability to represent and use numerosity is probably widespread among many animal species,” says Michael Beran, a comparative psychologist at Georgia State University in Atlanta. Moreover, he says, the study suggests that other creatures may possess the “foundational mechanisms” that enable humans to reason so well with numbers and that “perhaps even advanced mathematical abilities may be found in other animals.”

This article is adapted from ScienceNOW, the online daily news service of the journal Science.