Racing pigeons can count, at least as well as rhesus monkeys, New Zealand research has found.
The study adds to a growing body of work showing birds have abilities once considered unique to primates.
The authors, at Otago University's department of psychology, published their results in the latest edition of the US magazine Science.
The pigeons were given similar number-recognition tasks completed by rhesus monkeys in previous research carried out at New York's Columbia University.
The birds put images in order based on the number of objects pictured in each.
Other research has shown the western scrub-jay, found in western United States, can recollect specific past events, and New Caledonian crows can make and use tools.
"Indeed, over the past two decades the intellectual status of birds has risen markedly," the Otago researchers say.
Having said that, lead researcher and psychologist Damian Scarf tried using chickens for the numerical testing and found they were idiots.
He also found magpies didn't like laboratories, before achieving success with pigeons.
"They really are the perfect subjects and work diligently for their wheat reward," Dr Scarf told the New Zealand Science Media Centre.
He now plans to test parrots including the South Island kea, which have been claimed to have some of the intelligence of a six-year-old child.
"I am currently setting up a project that will utilise the two keas and other parrot species housed at the Dunedin Botanic Garden aviary," Dr Scarf said.
NZN