Although many species, from bees to elephants can distinguish among stimuli of varying quantities, apart from humans, only primates such as lemurs and chimps, were thought to have the ability to employ abstract numerical rules and reason numerically. However, according to a short research report published online in the journal Science on 23 December, researchers have discovered that pigeons can count as well as monkeys, and they suggest the ability is more widespread in the animal kingdom than we might assume.
Damian Scarf is a comparative psychologist at the University of Otago in Dunedin, New Zealand and lead author of the pigeon study described in the report. He told ScienceNOW that since 1998, when scientists showed that rhesus monkeys have an understanding of ordinal number (that is they can arrange any two sets of objects in order according to their quantity from one to nine), others have found this ability is consistent across all primate species. However, it was assumed this ability was unique to primates, so Scarf and colleagues decided to investigate further – using pigeons.
They took a year to train the pigeons to learn to discriminate one, two and three. They showed the pigeons a computer screen displaying objects of various shapes and colours. However despite the objects being of random shapes and colours, they always appeared in groups of one, two and three, so the pigeons learned to peck at the groups in order of how many objects were in them and nothing else.
When they got it right, that is they pecked at the groups in the correct ascending order, for example one yellow rectangle, two red ovals, three yellow bars, the pigeons got a food reward.
In the next phase of the test, the researchers presented the pigeons with two sets containing between one and nine objects, even though they had only been trained to put sets containing one, two and three in order.
But the pigeons didn’t hesitate to peck out groups of new numbers of shapes, for instance five ovals or seven rectangles. And they got it right far more often than would be expected by mere chance.
Elizabeth Brannon, a cognitive neuroscientist at Duke University in Durham, North Carolina, was the lead author on the original rhesus monkey study. She told ScienceNOW she remembers being amazed to discover that monkeys had numerical reasoning ability. But she added we should be “even more impressed” to find pigeons can do it too.
Perhaps the same neural mechanism helps both primates and pigeons to have this ability, she said, adding that the new study suggests although the evolutionary descent of pigeons and monkeys diverged hundreds of millions of years ago and their brains are organized completely differently, they appear to solve the problem in the same way.
Scarf and colleagues suggest other species may also have this ability, or something similar.
Written by Catharine Paddock PhD