Daniel Sol of the Universitat Autonoma de Barcelona in Spain, Louis Lefebvre of McGill University in Montreal in Canada and colleagues in Britain and New Zealand studied reports from bird-watchers around the world.

They gathered data on brain mass for 1,967 species.

In more than 600 introductions of nearly 200 bird species into new habitat they found that species with brains large relative to their body size tended to survive better in new environments than smaller-brained birds.

Examples include the introduction in the 19th century of the European starling to North America.

"Overall, our results provide strong evidence for the hypothesis that enlarged brains function, and hence may have evolved, to deal with changes in the environment," they wrote in this week's issue of the Proceedings of the National Academy of Sciences.

The researchers last month published an IQ index guide to birds that show corvids -- birds from the crow family including ravens and jays -- are by far the cleverest birds.

Next on the list are hawks, woodpeckers and herons, while partridges, new world quails, emus and ostriches are the dolts of the bird world.

Parrots only rate an average score despite their particularly large brains and abilities to mimic human speech, Lefebvre told a meeting in February of the American Association for the Advancement of Science.

Lefebvre said his team has also documented odd examples of bird intelligence such as vultures that would wait on fences marking off mine fields in Zimbabwe, waiting for errant animals to meet their ends and provide a meal.

"They would actually perch on the barbed wire and wait for the minefields to give them chopped antelope," Lefebvre told reporters.

Japanese crows were observed leaving nuts at busy intersections for cars to crack for them, he said, even making use of red lights and crosswalks to do so safely.