When it comes to birds, males—with their bright feathers, extra accessories, and impressive mating displays—tend to get all the attention. But for many birds, such as the Choco Toucan pictured above, brilliant plumage has nothing to do with sex, and everything to do with survival.
That, at least, is the conclusion of researchers at the University of Wisconsin-Milwaukee, after comparing male and female plumage in nearly a thousand species of birds. The researchers found that while males often have brighter feathers than females, guys and gals are actually more similar than they are different. Because color affects things like predator avoidance and foraging success, it's driven by natural selection as much as sexual selection.
"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 in their paper.
In science, when we notice a difference between two groups, it's our natural tendency to focus on why that difference exists. When studying birds, biologists have long been struck by color variation between the two sexes. Since the time of Darwin, we've attributed the phenomena almost exclusively to sex: Brighter, more colorful males tend to attract more mates and pass along more of their genes.
While this approach is not wrong, thinking only about differences can lead us to overlook important aspects of an animal's ecology. For instance, in the present study, the researchers discovered that when the sexes became more similar in color, they did so for reasons of natural selection, such as predator avoidance, rather than sexual selection.
"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 in a statement.