Why Island Birds Have Bigger Brains Than Their Mainland Counterparts

Researchers measured the brain sizes of 11,554 birds, including representatives of 110 island-dwelling species and 1,821 continental species

The New Zealand Tomtit is one of the island-dwelling species included in the study Jon Sullivan / CREAF

It’s a classic chicken-versus-egg quandary: Are big-brained—and therefore smarter—birds more likely to find their way to islands, or does island living trigger brain growth?

Scientists have long suspected the latter, but all they had to support the claim was anecdotal evidence. Now, a new study published in Nature Communications provides data that confirms the connection between brain size and island environments, vindicating previous researchers—and perhaps proving that the phrase “birdbrain” isn’t necessarily an insult.

Cosmos Magazine’s Tanya Loos reports that an international team of researchers led by Ferran Sayol of Barcelona’s Ecological Applications and Forest Research Centre measured the brain sizes of 11,554 museum specimens, including representatives of 110 island-dwelling species and 1,821 continental species. Island birds across the board exhibited bigger brain sizes than their mainland relatives, but the question of whether this growth precipitated or followed island colonization remained unanswered.

To resolve the debate, the scientists revisited their dataset. By comparing the relative brain sizes of closely related island and continental birds, they discovered that birds that evolved on an island over a long period of time had bigger brains than their non-island dwelling cousins, Bob Yirka writes for Phys.org.

Avian species tested ranged from the notoriously smaller-brained pigeon to the crafty, tool-wielding New Caledonian crow. This diverse assortment enabled the team to track trends across multiple bird families known for their intelligence (or lack thereof). Regardless of the species tested, findings remained consistent—island birds developed advanced cognitive abilities as a direct result of their environment.

Evolution on islands gets weird, notes Forbes. Since islands are isolated, there are fewer species to compete with, but resources are limited and the pace of life is generally slower.

This means that because small patches of land tend to be inhabited by fewer species than the mainland, island dwellers are free to pursue new food opportunities, or carve out a niche for themselves, without the added pressures of inter-species competition and predators. The relative isolation of most islands means there’s no “plan B” if their habitat deteriorates, so an animal’s brain function must adapt easily in order for it to survive.

“The need to adopt new resource opportunities by island colonizers should select for enhanced cognition and larger brains,” Sayol explains in a blog post. “Selection should be particularly strong due to the limits to dispersion, which would prevent individuals from moving to other places when environmental conditions deteriorate.”

The third potential explanation for island birds’ bigger brains is their slowed-down pace of life. (Just think of the popular beachgoers’ excuse for indulging in relaxation: “I’m on island time.”). The study states that island species tend to mature more slowly than their mainland brethren, which gives them enough time to develop the big brains needed to survive in an environment where cleverness prevails.

As Forbes concludes, “Since learning and behavioral flexibility ultimately provide big payoffs to island species when local conditions become more challenging, such an evolutionary innovation could quickly spread through the population."

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