An international team of scientists has figured out why Gouldian Finches continue to feature three different colors: red, yellow, and black.

In a study, they explained that another evolutionary process maintained the polymorphism of the popular cage birds over thousands of generations.

The team consists of researchers from Cornell University's Lab of Ornithology, University of Sheffield, and other institutions. They published their findings in the journal Nature Communications on Wednesday, April 23.

Why Gouldian Finches Have Different Color Heads

"Having distinct multiple color types — a polymorphism-maintained within a species for a long time is extremely rare," explained David Toews, a postdoctoral researcher at the Cornell Lab and a co-author of the study.

"Natural selection is typically thought of in a linear fashion — a mutation changes a trait which then confers some reproductive or survival advantage, which results in more offspring, and the trait eventually becomes the sole type in the population."

Toews and team explained that another evolutionary process called balancing selection has maintained the red and black tone of Gouldian Finches. Studies conducted by Macquarie University found that male Gouldian Finches with a red head are more popular to the females. Red-headed finches are also more dominant within the birds' social hierarchy.

However, red-headed finches also have disadvantages. The research found that they have higher levels of stress hormones during a competition, canceling out its advantage over black-headed finches.

The mechanism that maintains the existence of yellow-headed Gouldian Finches, which makes up less than one percent of the wild finches population in the world, remains a mystery.

How Gouldian Finches Get Their Vibrant Colors

Separate teams from the University of Sheffield and the Cornell Lab independently investigated the gene called follistatin, which can be found in the sex chromosomes of Gouldian Finches. The researchers combined their data and reported that the gene regulates the melatonin that produces the red and black colors of the Gouldian Finches' head.

However, a different gene not located in the sex chromosome and not yet been found by scientists is responsible for the yellow head of some Gouldian Finches.

In addition, the researchers revealed that the same genes are also likely to be responsible for the color of the plumage of North American Blue-winged and Golden-winged warblers.