Late last month, a woman in Alabaster, Alabama spotted an unusual bird in her backyard feeder, which was soon revealed to be an extremely rare yellow-pigmented Northern cardinal.
Auburn University biology professor Geoffrey Hill said the cardinal in the photos is an adult male in the same species as the common red cardinal, but carries a genetic mutation that causes what would normally be brilliant red feathers to be bright yellow instead.
Alabaster resident Charlie Stephenson first noticed the unusual bird at her backyard feeder in late January and posted about it on Facebook. She said she's been birding for decades but it took her some time to figure out what she was seeing.
"I thought 'well there's a bird I've never seen before'," Stephenson said. "Then I realized it was a cardinal, and it was a yellow cardinal."
… Hill — who has literally written books on bird coloration — said the mutation is rare enough that even he, as a bird curator and researcher has never seen one in person.
"There are probably a million bird feeding stations in that area so very very roughly, yellow cardinals are a one in a million mutation."
However, an expert at the National Audubon Society has a different theory on why the bird's plumage is yellow:
As Geoff LeBaron, Audubon's Christmas Bird Count director, points out, the cardinal's crest and wing feathers look frayed in photos. While wear and tear is a natural part of a bird's life, it can be exacerbated by a poor diet or environmental stressors. These health issues could also lead to changes in how carotenoids—plant-based pigments that turn feathers red, orange, and yellow—are expressed.
Although this alternative theory is plausible, ultimately, LeBaron agrees that genetics could be the sole factor. But the only way to solve the case is to wait for the cardinal to swap its feathers. "Time will tell with this bird," LeBaron says. If it sticks around Alabaster and is still yellow next winter, a mutation is the likeliest culprit. But if it comes out red after another molt, it means the bird somehow recalibrated its pigments.