When Alabama resident Charlie Stephenson peered out her window last month, she was surprised to see a large yellow bird perched at her feeder.
"I thought 'Well, there's a bird I've never seen before'," the bird enthusiast told AL.com. "Then I realized it was a cardinal, and it was a yellow cardinal."
Found throughout much of North America, the northern cardinal is better known for the brilliant crimson red exhibited by adult males. The birds, and other colorful feathered species, attain their beautiful feathers by consuming pigments called carotenoids and converting them via a special enzyme.
According to Geoffrey Hill, an Auburn University professor of biology and co-author of a 2003 study on the coloration phenomenon, the yellow yellow cardinal at Stephenson's bird feeder likely has a mutation.
"Because songbirds like cardinals attain red coloration by converting dietary yellow pigments to red feather pigments, the most likely explanation for yellow instead of red feathers is that the conversion process isn’t working," he told MNN. "It almost surely has the enzyme, but something in the process of making the enzyme work has gone wrong."
While the phenomenon of a yellow cardinal is exceedingly rare, it's not something specific to any one species.
"Odd coloration — all white, all black, yellow instead of red, fawn instead of brown — occur in essentially all species of birds and mammals (including humans) but always as extreme rarities," Hill added. "These extreme rarities are the basis for the color varieties of canaries, budgies, bunnies and ferret that you can see at any pet shop."
The sighting of this particular yellow cardinal is receiving plenty of adoration online, but it's certainly not the first one to grace social media. In 2014, Andy Magee posted a video of a yellow variety he spotted in the suburbs outside St. Louis.
Sometimes, as shown in the video below, male cardinals can also come in a kind of hybrid orange shade.
The only downside to a male cardinal sporting yellow instead of its customary rouge may be the way it attracts a mate. According to the Cornell Lab of Ornithology, research indicates that brighter red males have higher reproductive success. As a result, this likely plays a big role in why we're not likely to see more yellow cardinals at our bird feeders in the future.
"If sexual selection theory is correct, he will be a loser," Hill added to MNN.