A pigeon responds to images on a touch screen at the University of Otago in… (William van der Vliet )
For typical city folk, there may be no creature more pedestrian than the pigeon, that ubiquitous gray denizen of the sidewalks. But the bird's reputation got a boost this month when psychologists at the University of Otago in Dunedin, New Zealand, announced that pigeons can count — a skill previously presumed to be unique to primates.
The finding, which was published in the journal Science, is forcing experts to reconsider the evolution of mathematical ability. Postdoctoral fellow and study leader Damian Scarf explained why in a conversation with The Times.
Why study pigeons?
Comparative psychologists study a range of animals to figure out the evolution of different abilities.
Pigeons are just perfect subjects. They're really good experimental animals. They are really easy to train, they're really diligent workers — and they are interesting because they're not a mammal, so their brains and their evolution are different. They split from mammals about 300 million years ago.
This research gives us an idea of the basic neural machinery required for these numerical abilities. It shows that you don't need a brain like a primate's or a mammal's to be able to form these abstract concepts.
How are bird brains different?
Primates have a layered cortex, but pigeons don't. The way their brains are organized is very different. But it seems that everything we have they have — it's just packaged in a different way.
How do you test a bird's ability to understand a mathematical concept?
The pigeons respond on touch screens. Pictures come up on the screen, the pigeons peck at them, and the touch screen registers their response.
In this case, we had three images: One had one object in it, another had two objects, and the third had three objects. We trained the pigeons to peck the pictures in ascending order.
We gave them lots and lots of these sets, with different shapes and sizes of objects, basically just reinforcing the one-two-three rule. They got a reward every time they got a correct response — a hopper gave them a little basket of wheat that they could peck from.
We trained them for a long, long time. Then we tested them with tiers of images, with numbers that were outside of that range, to see if they could transfer that ascending rule to novel numbers such as four and five and six and seven. They were able to do that as well as monkeys were, which was really surprising.
How long did it take to train the pigeons?
It took about an hour a day, seven days a week, every day for a whole year.
Your study in Science reported that the bigger the difference between numbers shown during testing, the better the pigeons performed. Why is that important?
It's significant because it basically shows us that their way of processing the stimulus is similar to how we would process it. If you tested humans, you'd get the same effect. You'd also get the same effect if you tested adults' ability to order letters in the alphabet. The greater the distance between letters, the easier adults can tell you which one comes first.
Have researchers tried this out on many other animals?
No, it's just been primates and pigeons. Psychologists Elizabeth Brannon and Herbert Terrace tested rhesus monkeys in 1998, and since then people have looked at baboons, Capuchin monkeys and, most recently, lemurs.
We're the first ones to look outside of primates. The pigeons performed better than the lemurs.
What does this tell us about how math skills evolved?
One interesting question is, did numerical competence develop just in primates? Is it general to mammals or is it shared by groups outside of mammals? Testing pigeons allows us to show that this ability is not restricted to primates or mammals, and that gives us another clue about the evolutionary process.
It could be derived from a common ancestor of primates and birds that lived 300 million years ago before the species split, or it could have evolved independently.
Why would evolution favor the ability to count and understand abstract numerical rules?
It was probably driven by the search for food. To forage optimally, pigeons — and primates — would need to be able to distinguish which area is going to be more productive. I think it's probably based on something simple like that.
Do you have a hunch about whether counting evolved separately in birds and mammals, or was inherited from a shared early ancestor, like a reptile?
If I was going to have to go one way, I'd probably say it evolved independently. I think if the skill had evolved 300 million years ago, it would be very widespread today. But this is a difficult ability, so I don't think that's the case.
Do you plan to test other types of animals?
I'm planning to test more bird species, including African gray parrots and cockatoos. Parrots are thought to be quite smart. I'm eager to see how that goes.