September 5, 2008
Northern Mockingbird
Northern Mockingbird
I've been photographing birds for several years working under the conceit that if I'm not moving, the birds can't see me, especially if I'm wearing camouflage.  Recent studies by Muir Eaton, a postdoctoral researcher at the University of Kansas (a fellow Jayhawk!), have shown this may not be entirely true.  It had been known for some time that certain birds had ultraviolet (UV) vision, but Eaton discovered it's most important use and just how widespread it really is.

We all know examples of avian sexual dimorphism, males and females of the same species that wear strikingly different plumage.  The deep red male cardinal and its drab brown female are a good example.  Most of us assume birds see like we do and that these visual differences help them find a mate.  But how does this work for over half of the world's songbird species which are monochromatic?  The sexes look the same.  Or at least they do to us.

Under a spectrometer, Eaton examined the feathers of many songbird species monochromatic to our eyes, and found over 90 percent were, in fact, dichromatic, primarily because feather patches on various parts of their bodies reflect UV light.  We can't see it, but they can.  They don't look the same to one another.  Among the families of birds known to see UV light are songbirds, hummingbirds, parrots, and gulls.  Raptors and crows cannot.

This explains how many species distinguish between gender even though we cannot, and why many species can practice elaborate courtship displays without fear of attracting predators.  It also sheds light (pardon the pun) on our own species' anthropocentric view of the natural world.  Sorry, but it's not all about us.

Here in Arizona some of the formerly assumed monochromatic species include both the least and most colorful.  Who knows whether the neighborhood mockingbird is a male or a female, or if you're seeing the same one all the time or a pair?  You don’t, but it's for sure they do.  Mockingbirds' UV patch is on their chest.  And the beautiful Painted Redstart, coal black with white wing patches and scarlet belly?  It's UV patch is on its throat which is just coal black to our eyes.

If birds were listers, their lists would far surpass ours.  Listers all know several "sibling" species, almost impossible to distinguish from one another in the field, and often wonder why or if they don't interbreed.  Eaton's research, of course, gives us the answer.  And if you were on the beach in San Diego this summer and wondered if the sunbathers were wearing UV sunscreen, the seagulls flying overhead could have told you.

Birds don't see like we do, and on some levels where it enhances their chances for survival, they see better. They see a broader range of colors and finer differences between those colors than we can.  And they probably see me, even in my camouflage, and they're probably laughing as they put me down on their weird-looking bipeds-seen list.