Pigeons perform just as well on certain math tests as monkeys do, scientists in New Zealand have found.

While the birds may not seem very bright at first glance, they can be trained to use abstract mathematical rules to decide which of two images contains a higher number of elements such as circles, squares and triangles, according to a study published Thursday online in Science.

Previously, scientists had thought that only humans and other primates could learn the abstract math skills needed to put numbers in order.

"Our research not only shows that pigeons are also members of this exclusive club, but, somewhat surprisingly, their performance is on a par with that of monkeys," said Damian Scarf, a psychology researcher at the University of Otago in Dunedin who led the study, in a statement.

"Our findings add to a growing body of evidence that pigeons are among a number of avian species exhibiting impressive mental abilities that really do give the lie to the old ‘bird brain’ insult."

Scarf and his colleagues trained and tested a group of pigeons using the same method used 15 years ago to show that macaque monkeys could learn abstract numerical rules.

They taught three pigeons to peck, in ascending order, lists of three items that consisted of one, two or three shapes that sometimes varied in size, shape and colour. If they completed the task correctly, they were rewarded with some wheat.

Then the researchers tested the birds with pairs of images that each contained one to nine objects, to see if the birds could order numbers that they had not explicitly learned.

Over 10 test sessions, the birds scored over 70 per cent correct, even when both numbers were not familiar to them. In fact, their scores were quite similar to those of the monkeys on similar tests. Like the monkeys, they were more accurate and responded more quickly if there was a bigger difference between the two numbers.

Both monkeys and pigeons tended to have more trouble distinguishing between smaller numbers of objects, even though those were the numbers they originally trained with.

The researchers said they don't yet know whether pigeons' and monkeys' mathematical abilities come from a common ancestor or whether they evolved independently.

During the next phase of their research, they want to monitor the birds' brain activity while they perform tasks involving math. They also want to test a species of parrot native to New Zealand called the kea, which is reputed to unusual intelligence.