By Paul Rincon
BBC News science reporter, in Washington DC
Crows and jays are the brain boxes of the bird world, according to a Canadian scientist who has invented a method of measuring avian IQ.
Crows acquire food in inventive ways
The IQ scale is based on the number of novel feeding behaviours shown by birds in the wild.
The test's creator Dr Louis Lefebvre was surprised that parrots were not high in the pecking order - despite their relatively large brains.
The research was presented at a major science conference in Washington DC.
The avian intelligence index is based on 2,000 reports of feeding "innovations" observed in the wild and published in ornithology journals over a period of 75 years.
"We gathered as many examples as we could from the short notes of ornithology journals about the feeding behaviours that people had never seen or were unusual," said Dr Lefebvre, of McGill University in Montreal, Canada.
"From that we established different numbers for different birds. There are differences. There are some kinds of birds that score higher than others.
"The crows, the jays, that kind of bird - the corvidae - are the tops; then the falcons are second, the hawks the herons and the woodpecker rank quite high."
Dr Lefebvre said that many of the novel feeding behaviours he included in the work were mundane, but every once in a while, birds could be spectacularly inventive about obtaining their food.
During the war of liberation in Rhodesia, now Zimbabwe, a soldier and avid bird watcher observed vultures sitting on barbwire fences next to mine fields waiting for gazelles and other herbivores to wander in and get blown to smithereens.
"It gave them a meal that was already ground up," said Dr Lefebvre.
"The observer mentioned that once in a while a vulture was caught at its own game and got blown up on a mine."
Another bird watcher observed a great skua in the Antarctic who joined in with seal pups feeding on the milk from their mother.
Many of the birds that ranked high on the innovation scale are the least popular with the public.
"When you look at published reports on whether people like birds or don't like birds, they don't correlate well with intelligence," said the McGill researcher.
"People tend not to like crows, because they have this fiendish look to them and they're black and they like dead prey. Warblers and the birds that people tend to like are not the high innovators."
But Dr Lefebvre said the scale did not measure how smart birds were, only how "innovative".
"With the word 'smart' you have to have a value judgment. You can never know whether a bird has been learning by observation or has figured something out by itself."
The work was presented to the annual meeting of the American Association for the Advancement of Science (AAAS).