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Colorful bird plumage is about survival, not just sex

"This should hopefully get researchers to think more about how color affects survival, especially predation and foraging success, in both sexes," said study author Peter Dunn.

By Brooks Hays
A pair of Gouldian Finches. Photo by Nigel Jacques/CC
A pair of Gouldian Finches. Photo by Nigel Jacques/CC

MILWAUKEE, March 31 (UPI) -- Ornithologists and evolutionary biologists have long agreed that the quest for a mate encourages male birds to take on brighter and brighter colors. It is true that for many bird species, male specimens exhibit brighter and more varied coloration.

But a new systematic analysis of hundreds of bird species proves the two sexes have more in common than they do differences. Researchers at the University of Wisconsin-Milwaukee also found that males and females adopted more similar colors and shades over time, in an effort to blend into their habitat and avoid predation.

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The evidence, researchers say, suggests that ecology and behavior -- the pressure of surviving migration, breeding in subtropical climates and raising offspring -- are equal to sexual selection in influencing outward appearance.

"Although most studies of bird plumage focus on dichromatism, evolutionary change has most often led to similar, rather than different, plumage in males and females," the authors write.

Along with lead study author Jessica Armenta, a former grad student, ecology professors Peter Dunn and Linda Whittingham analyzed male and female specimens from 977 bird species -- scoring each on brightness and hue, and comparing them to various measures of natural and sexual selection.

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Their research confirmed that when color differences between males and females grow, it is due to sexual selection. But just as often, color differences shrink as a result of natural selection. Additionally, some male birds -- like red-winged blackbirds -- with duller feathers were found to secure more mates than their brighter-colored peers.

"A lot of research has focused on how plumage color is related to mating success, especially in males," Dunn explained in a press release, "so this should hopefully get researchers to think more about how color affects survival, especially predation and foraging success, in both sexes."

The new research was published this week in the journal Science Advances.

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