The brilliant red plumage on many bird species isn’t just pretty; it has a purpose. Male House Finches with bright red coloring, for example, more easily attract mates. And the scarlet shoulder patch on Red-winged Blackbirds helps males defend their territories. Red feathers have long posed one mystery, however: Scientists didn’t know how birds grew them. Today, a team of researchers thinks it may have finally figured it out.
With the exception of a few parrots and turacos, most birds acquire warm colors from molecules, called carotenoids, in the food they eat. But carotenoids produce a yellow pigment, meaning some birds must be able to transform it to a red one. Auburn University ornithologist Geoff Hill has spent nearly a decade trying to understand the biochemistry behind that color conversion. The breakthrough finally came courtesy of an international collaboration and a century-old experiment in bird breeding.
One of the genes, called CYP2J19, creates an enzyme known to interact with carotenoids. Most birds carry it—the researchers found CYP2J19 expressed in the retinas of yellow canaries and domestic chickens (they surmise it allows them to better perceive red light). Birds like the Red Siskin and red canary, on the other hand, express that gene in their livers, skin, and feathers, which suggests that it’s critical for producing red plumage.
“The cardinal, for example, is a very iconic and well-known red bird, but every once in a while in nature you see a yellow cardinal,” says Corbo. “These have been well documented, but they’re very rare.” The team suspects that yellow cardinals have a mutation in the same gene as the red canary, only preventing the growth of red feathers. To find out, they’ve recently gotten their hands on some genetic material from a yellow cardinal preserved in a natural history museum. They hope its plumage conceals insights.
Sometimes it is the exception that proves the rule ...
So this looks like another instance where two mutations are needed to express red color in wings, the end result is beneficial in that it leads to better mating success and this passes the genes to following generations.