Wet encrustations of snow forced dozens of birds to the sunflower seed feeder. All their usual feeding places, the nooks and crannies in bark, are plugged with frozen flakes.

Hard times for birds create interesting viewing opportunities for humans and other mammals with keen ornithological interests. We stay inside and watch through the windows.

Of course, we also have the old standby, “cardinals in snow,” an image found on so many greeting cards, mailbox paintings, Christmas shopping flyers, nature magazines, and, yes, blogs, that the weight of accumulated cultural exposure squashes the actual experience.

My thought on seeing them was, Oh how cliché, an absurd response to the sight of birds that were minding their own business as they fed on my sunflowery largess. Once I got over my overly puffed up horror at participation in such a tawdry aesthetic experience, I saw them with new eyes. They were stunning.

So, what is it about red-on-white? Our eyes are easily beguiled: cardinals in snow, STOP signs, Texaco, the Red Cross, Marilyn Monroe’s lips, Coca-Cola, candy canes, and flags, endless flags (USA, Japan, Canada, England, Poland, Turkey, Singapore, it goes on…). None of these are particularly subtle signals. The recurring theme is, “gimme your attention.”

So, why does it work? The contrast of hue and saturation obviously helps. But so does our heritage as primates. We’re unusual among mammals in being able to “see red.” In fact, most mammals lack the right type of receptor cell in their eyes and so miss out on the cardinals’ display. Only in one lineage of primates did this receptor evolve, probably to see red fruits (our monkey cousins still eat actual fruit, we use the receptor to find candy and sodas, then to define national boundaries — that’s evolutionary progress for you). So thank you, mutant ancestors, for my experience of the cardinals’ winter glory.

The cardinals themselves have an even richer experience. Not only do birds see red, but their receptors open the UV-range of light to them. We can’t begin to imagine the experience of these extra colors. What does snow look like in UV?