Species of birds that live on oceanic islands (islands that rise from the ocean floor due to seismic or volcanic activity) have larger brains than their mainland relatives according to research published in Nature Communications. The study suggests that these differences are the result of evolutionary processes that took place on islands as opposed to differences in colonisation success.

The use of tools by the New Caledonian crow, the Hawaiian crow and the Galapagos woodpecker finch suggests that islands may lead to the evolution of advanced cognitive abilities. However, only two studies to date have investigated whether island species differ in relative brain size from continental species: a study of crows and ravens, and another in primates. Neither study found an association between brain size (relative to body size) and island living.

Using a dataset of brain sizes for 11,554 specimens from 1,931 bird species (110 avian species living on oceanic islands and 1,821 continental species), Ferran Sayol and colleagues found that birds living on oceanic islands tend to have larger brains than those from closely related mainland species. The authors suggest that this is because island living makes the environment more unpredictable, which in turn, selects for larger brains. On islands, there are limited possibilities to disperse when conditions deteriorate, which may force individuals to explore and rely on more elaborate behavioural responses.