A highly-endangered rainbow bird, breaking the rules of evolution, has long mystified scientists with its heads of many colours.
The Gouldian Finch has three distinct colour types of finches, with either red, black or yellow heads, something that is seen as extremely rare over the course of generations.
Now scientists from the University of Sheffield, working with the Cornell Lab of Ornithology, have discovered a gene that allows it to happen.
This gene, called follistatin, regulates melanin to produce either red or black-headed finches, the scientists say.
But they are still stumped, they admit, when it comes to the yellow-headed type of bird, which makes up less than one per cent of the Gouldian population.
This type is produced by a completely different mechanism, the scientists add, one that is not yet understood.
Lead author of the paper Kang-Wook Kim, from the University of Sheffield’s Department of Animal and Plant Sciences said: “Most people have heard of natural selection, but survival of the fittest cannot explain the colour diversity we see in the Gouldian Finch.
“We demonstrate that there is another evolutionary process - called balancing selection - that has maintained the black or red head colour over thousands of generations.”
The study shows that the red-headed finches are more dominant and preferred by female finches.
The black-headed finches haven't though, with the scientists warning there are disadvantages to having a red head - including higher levels of stress hormones and poorer reproductive outcomes.
Co-author of the paper David Toews, a PhD researcher at the Cornell Lab, said: “Having distinct colour types – a polymorphism – maintained within a species for a long time is extremely rare.
“Natural selection is typically thought of in a linear fashion – a mutation changes a trait which then confers some reproductive or survival advantage and the trait eventually becomes the sole type in the population.
“If advantages are cancelled out by concurrent disadvantages, these two colour types can be maintained, that’s balancing selection. Red forms are not as common in the wild, so the counterbalancing pressure reduces the advantage of being red.”