By now, we all know that being called a "birdbrain" isn’t really an insult; birds have been shown to have several higher-order cognitive skills that we previously thought only primates had the brains for. Jays are capable of episodic memory, parrots can solve multi-step puzzles and use a succession of tools to get a food item, and crows have even learned to use city traffic and stoplights to their advantage. Now, Science reports yet another cognitive area where birds are on par with primates: they have a sense of numbers.

In 1998, a pair of researchers used a novel experiment to show that rhesus monkeys had numerical competence; in other words, they could use abstract numerical rules. The monkeys were shown a set of three images picturing one, two, and three items, and were trained to choose these images in ascending order. Once they had been trained to a certain accuracy level, they were shown numbers of items that they hadn’t necessarily seen before. The monkeys were generally able to choose the greater of the two numbers, even when they didn’t have experience with the values involved. Clearly, they had learned not only the values they were trained on, but also more abstract rules about numerosity.

The authors of this week’s Science article tested pigeons in the same way. They were taught to order 35 different sets of images, all of which displayed one, two, or three items. Then, the setup changed: values up to nine were introduced. The pigeons were then shown a pair of two familiar numbers (such as two and three), one familiar and one unfamiliar number (such as one and seven), or two unfamiliar numbers (such as five and eight).

Not surprisingly, the pigeons did well at the task comparing two numbers they had been trained on. However, they also performed very well on the other two tasks, choosing the greater number in more than 90 percent of the trials with the familiar-novel pairs, and about 75 percent of the time in the trials with the novel-novel pairs. The pigeons’ accuracy was lowest when the distance between the two numbers was small and when the ratio of the numbers was close to 1.

Overall, the birds performed about as well as the rhesus monkeys had in the original experiment. Both species are certainly capable of learning a simple mathematical rule, then using that rule in a more abstract sense to handle new values. So the obvious question now is whether the two species share a common ancestor with a keen number sense, or whether they both acquired their numerical competence through convergent evolution. Unfortunately, as the answer so often is in science, we don’t know yet.

Science, 2011. DOI: 10.1126/science.1213357 (About DOIs).