It's a truth more or less universally acknowledged that the northern cardinal is the first bird that sends young birdwatchers to a field guide. After all, who can resist admiring the bright red plumage of the tufted little visitor in the yard, especially on a dull midwinter morning when the sky and earth are a nondescript shade of gray?
It's been equally acknowledged that the redness of the male Cardinalis cardinalis is a status symbol. The redder his feathers, the more desirable he is as a mate. And this is no superficial preference on the part of the female cardinal (she herself brown with just a blush of red). The male gets his color from the carotenoids in his diet, so a richer red is a good indicator of his access to food, the state of his health, and the quality of the territory he controls. In other words, as studies have shown, redness correlates very well with reproductive success.
At least that's the way it's been up to now. But like many other avian species, the northern cardinal is living in an increasingly urban environment. For urban cardinals, the brightness of feathers may cease to correlate with good health and high status, and sexual selection by color may prove meaningless.
A recent three-year study showed that among urban northern cardinals the brightness of the red feathers was not a good predictor of reproductive success. Why? The cause seems to be Amur honeysuckle, an invasive species rich in carotenoids. If the rural birds rely on the honeysuckle for sustenance, their feathers become very red. But urban birds have more varied sources of food, such as the rich seeds in our backyard feeders. These seeds are poor sources of carotenoids so the cardinal who eats them won't be the brightest bird around, but he might be very strong and healthy, a fit mate, nonetheless.
Does this mean that the female cardinal living in the city will become more sophisticated, less prone to be dazzled by flashy color when she chooses a mate? Perhaps. And perhaps in time the males will become a shade or two duller.
But whatever his shade of red, Cardinalis cardinalis will certainly continue to rivet human attention and will most likely remain among the most reported species in the GBBC, as he was this year.