Wondrous Wildlife
By Vern and Lori Gieger
Do You See What I See?

     Often we are asked whether one of our animals is a male or female. Sometimes it is obvious or easy to tell by merely looking at the animal in question. However that is not always the case, especially when it comes to birds. There are many species that to the human eye the male and female look identical. But are they really identical? Ultraviolet - just one more color. But if you can’t see it, you’re missing a lot.
     We readily accept that a dog’s sense of smell is far superior than our own, yet we ignore the possibility that animals see things that are beyond our ability to perceive. Many animals advertise their attractiveness with flashy colors beyond the limits of human perception.
     So while they may appear identical to us, you can bet they don’t appear identical to each other. In nature, as in home decor, often the female does the choosing; however in nature the female often chooses her mate for his pleasing color. Girl guppies go for the guys with the biggest orange spots; female house finches fall for fellows with the brightest red feathers. Scientists call this process female mate choice.
     Ultraviolet indication is fairly well-known in the natural world; however the role of UV color in female mate choice is still relatively unexplored. Harvard researchers suggest that ultraviolet signals keep two look-alike butterflies, the orange sulfur and the clouded sulfur, from interbreeding. These small butterflies look virtually identical to the human eye. Both have bright yellow wings with black borders. But the wings of a male orange sulfur butterfly reflect UV light; the wings of a clouded sulfur do not. It is proposed that females use their ultraviolet vision to identify a mate of the proper species.
     What else may UV reveal to the prospective mate? It feels intuitively sensible that the best-dressed guy gets the girl. But, can a female be sure that flashiness equals great mate? Is the butterfly or bird with the brightest wings really the equivalent of a Harvard-educated /Olympic athlete? Or is he just an average guy in a discount Armani suit? Some studies suggest that the best-fed males and the males with the fewest parasites and best over all health had a higher intensity of their UV reflectance. So although they look alike to us humans, females can see the difference. One hypothesis is that colorful displays are an honest advertisement of some superior quality that leads to better reproductive success.
     UV color - seeing more than just red - red, yellow and orange pigmentation in feathers is often derived from food and is easily visible to humans as well as birds. But such carotenoid colors can also produce vivid ultraviolet reflections, which when seen in UV are not the same color. The scarlet ibis for example, might be more correctly named the ultra purple ibis.
     Many species of fish, insects, birds and reptiles see and respond to UV light. Bees follow UV reflecting nectar trails on flowers much the way airplanes follow runway lights. Desert iguanas mark the ground with UV-absorbing urine, leaving territorial signals that stand out against the UV-reflecting sand.
     The eyes of insects and birds are attuned to wavelengths of light outside the visible range that humans see in. Birds that appear drab to us are often radiant in colors we don’t even have names for, when seen in ultraviolet light.
     Perhaps you wish you could see the world the way birds and butterflies do. To some extent, you could, but the means is radical - cataract surgery. Ordinarily, the lens in the human eye screens out UV rays; but when the natural lens is replaced with a plastic lens, as in cataract surgery, UV rays can pass through. And human cones do respond just a bit, to near-ultraviolet light. This happened to a researcher’s mother; she started to see the nectar guides on flower petals! So seeing may be believing but, we have to learn to look carefully if we are to understand other animals because they, with their eyes, may be seeing things quite differently. We tend to trust our eyes. We believe what we see and assume that what we don’t see isn’t there. Sometimes that’s not true.