Bird colors and geography: New study sheds light plumage evolution

OKINAWA, Japan, Nov. 4 (UPI) -- Everything seems brighter in the tropics: the sky, the ocean, the houses, the birds. Think tropics and brightly feathered toucans and parrots come to mind. Why is that?

Some biologists have suggested the rich biodiversity of the tropics -- and the competition for mates -- drives brighter and brighter patterns. But new research suggests otherwise.

Scientist Nicholas Friedman found birds from the tropics aren't any more likely to be brightly colored than their peers in more temperate regions.

For his study, Friedman looked to Australia, the birthplace of songbirds. Evolutionary biologists believe songbirds began diversifying on the continent 30 million years ago, before departing to colonize other parts of the planet.

Friedman analyzed the color patterns of 137 species from two major songbird families. He and his colleagues at the Okinawa Institute of Science and Technology Graduate University then built a model to study the link between color, evolutionary relationships and geographic factors, including vegetation, precipitation, and humidity.

The results showed life in the tropics doesn't encourage more colorful feathers.

"If you look at birds in the tropics, there are a lot of colorful birds that stand out," Friedman said in a news release. "But there are really more species in general there, and there are just as many more of the little brown ones."

"Instead, birds living in the harsh arid climates of inland Australia tended to have fancier colors than those in the lush tropical islands," he added. "Since desert birds have to scramble for mates during the wet season, we think they may be evolving colors that can attract mates quickly."

The new findings -- published in the journal Global Ecology and Biogeography -- don't suggest geography and color are unrelated. Friedman argues the opposite, in fact. But the relationship isn't expressed across a scale from dull to colorful.

"The pattern is really clear," Friedman said, "birds living in the desert tend to be more grey on their backs, while birds living in the forest have evolved to be more of a dark green -- we think they are evolving these colors to match their background."