Gouldian finches are flashy birds. Native to Australia, they seem to wear a kaleidoscope of bright rainbow feathers. But there are three distinct color variations with individuals having a red, black or yellow head.
The rest of their brilliant bodies are a colorful mix of turquoise, purple, blue, yellow and green. But their heads are what drew the attention of researchers from the University of Sheffield in the U.K. and the Cornell Lab of Ornithology. They studied the evolutionary process at work behind this color selection. Their research was published in the journal Nature Communications.
"Most people have heard of natural selection," says lead author Kang-Wook Kim at the University of Sheffield, in a statement. "But 'survival of the fittest' cannot explain the color diversity we see in the Gouldian Finch. We demonstrate that there is another evolutionary process — balancing selection — that has maintained the black or red head color over thousands of generations."
Earlier studies found that red-headed finches appear to have an advantage. Female Gouldian finches with every color head prefer males with red heads. And red-headed male Gouldian finches are more dominant in the social hierarchy. (Yellow-headed Gouldian finches — which actually look orange — make up less than 1% of the wild population.)
So researchers wanted to know why the black-headed finches hadn't disappeared if red heads have so many advantages. They found that there are disadvantages to having that flashy red head, such as a lot of stress in competitive situations.
"If advantages are cancelled out by concurrent disadvantages, these two color types can be maintained — that's balancing selection," says co-author David Toews, who did this work as a postdoctoral researcher at the Cornell Lab and who is now at Pennsylvania State University. "Red forms are not as common in the wild, so the counterbalancing pressure reduces the advantage of being red. That's super cool!"