by Crystal Cockman
January 17, 2017
One of the more commonly seen birds in wintertime is the Northern Cardinal (Cardinalis cardinalis). Its range is southern Canada, through the eastern United States from Maine to Texas and south through Mexico. Males are bright red with a red-orange bill and a black face around the bill. Females are olive in color with red tinges on their wings, tail and crest. They do not migrate and do not molt into a dull plumage, so they stand out well against a landscape, particularly a snow-covered one. They are common at birdfeeders. They mate for life.
Birds have red feathers for a purpose – usually attracting a mate or defending their territory. But scientists have recently been studying exactly how a bird gets those red feathers. Most birds acquire warm colors from molecules, called carotenoids, found in the food that they eat. Carotenoids produce a yellow pigment, so some birds are able to transform this into a red color.
An Auburn University ornithologist named Geoff Hill researched the biochemistry behind this transformation. An experiment in bird breeding helped illuminate the answer. Breeders in the early twentieth century wanted to create a red canary. They bred a red bird known as the red siskin with the canary and the offspring had red feathers, and they bred that bird with another canary and so on until they had a bird that was mostly canary with red feathers.
A geneticist in Portugal named Miguel Carneiro studied the genomes of the red siskens, yellow canaries, and hybrids. The researchers identified two regions of the red canary’s genome that were inherited from the Red Siskin. The two researchers worked together to identify what the genes in those regions do. One of the genes, CYP2J19, creates an enzyme that interacts with carotenoids. Most birds have that gene, and the researchers found it expressed in the retinas of yellow canaries (believed to allow them to better perceive red light). However, birds like the red canary express that gene in their skin and feathers, thus producing the red plumage.
The second genomic region did not code for any specific enzyme, but was involved in the development of skin and feathers. The researchers decided that the birds needed the enzyme and the changes in the second genomic region for the pigments to turn the feathers red. Very rarely there are yellow cardinals, and scientists suspect that they have a mutation in the same gene as the red canary, except that it prevents the growth of red feathers.
What birds do you enjoy watching in the wintertime? It’s a great time of year to peep out your window and spy on birds feeding at your bird feeder, or to casually encounter them while walking around in the woods. I particularly love spotting a cedar waxwing or a Carolina chickadee. Winter is a favorite time for hiking for many people, and you never know what you might encounter. Maybe next time you’ll spot an elusive yellow cardinal. Whatever you see, it’s a great time of year to be outdoors.