Fine feathers: Why red birds look so fit and sexy

A red factor canary, created by breeding a wild South American bird called the red siskin with the common yellow canary. (David Carroll)

For birds like the cardinal, red coloring is extremely important. The brighter the hue on a male's feathers, the more likely a female is to take notice. Now two independent teams of scientists believe they've found the gene that allows birds to produce shades of red. And the identity of the gene might actually help explain why the color evolved in the first place.
"To produce red feathers, birds convert yellow dietary pigments known as carotenoids into red pigments and then deposit them in the feathers," Miguel Carneiro of the University of Porto in Portugal, who co-led one of the two studies published Thursday in Current Biology, said in a statement.

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"It was known that some birds have the ability to synthesize red ketocarotenoids from the yellow carotenoids that they obtain in their diet, but the gene or enzyme involved, and its anatomical location, have been obscure," added Nick Mundy of Cambridge University, an author on the second study.
Carneiro's group chose to study a trio of birds that have an intriguing, intersecting history: The red siskin is, of course, red, and comes by its color honestly — without human intervention. Canaries, as you probably know, are generally yellow (though they didn't start out that way). Enter the third star of the experiment, the "red-factor canary," which is a canary-siskin hybrid bred to have bright red feathers.
Because of the intersection of these birds' ancestry, scientists can use their genetic code to track down the genes that might specifically relate to redness.

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In analyzing the genomes of the red and yellow birds, the team found over 15,000 genetic variations that could be associated with red coloring. But one gene in particular, CYP2J19, really popped: It's active in the skin and liver, where the elusive enzymes responsible for producing red ketocarotenoids are thought to do their business. And it's 1,000 times more active in red birds than the yellow ones, the Atlantic reports. Lots of birds have this gene, but they only seem to use the proteins it controls in their eyes, where it produces red to act as a sort of filter and improve vision.

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