You have to give the lowly pigeon some credit. It thrives in some of the world's toughest environments - like London or New York. With apologies to Frank Sinatra, "If I can make if there, I'll make it anywhere."

Pigeons also understand some abstract mathematical concepts, report Damian Scarf and colleagues at the University of Otago in Dunedin, New Zealand. In a brief paper in the journal Science, they write that pigeons could rank objects in numerical order - something only seen before in humans and monkeys.

Scarf, a postdoctoral student in psychology, repeated an experiment done with rhesus monkeys in 1998. He trained pigeons to rank pictures with one, two or three New York taxicabs (well, actually, abstract colored objects) in them. When they pecked at them correctly in ascending order, they got a treat.

It didn't matter whether the objects were yellow or blue, round or square. What's more, they figured out unfamiliar numbers on their own. If they had been taught that two was more than one, they could also figure out that eight was more than five.

"Our results suggest that, at least with respect to numerical competence, pigeons are on par with primates," wrote Scarf et al, "and are well perched to inform us about the selection pressures and neural structures required for abstract numerical cognition."