The Nature of Seeing
By Susan Thurn,
Cable Natural History Museum
For four years now I have written this Nature Watch column every week. I have written about what to watch for in nature. I have received thousands of comments and heard stories from readers about their own observations in our north woods natural world. We are all phenologists, those who study the seasonal changes in nature, and we primarily do this through sight. We notice a movement out of the corner of our eye and suddenly see our first pileated woodpecker. A flash across the road comes in front of us and we have just spotted a timber wolf. It is our sight, an amazing sense, which provides such an important skill for discovering what surrounds us.
Our eyes contain many essential parts, but two of the most interesting to me include rods and cones. Inside our retina, a part of our eye the size of our thumbnail, are about 150 million light-sensitive rods and cones. Rods help us identify shapes using light. Cones identify color. Both cells then send information to the brain (believe it or not, the image sent to the brain is upside down, and then our brain turns the image right side up and interprets what we are looking at.) These are amazing details and operations that occur, but let us take a look at some specific animals and their visual adaptations.
An owl, if it could read, could read a newspaper from the other end of a football field. This makes sense since their eyes are one-third the size of their heads. They can see a mouse moving over 150 feet away with light equal to that of a candle. They can follow their prey with a head that can turn 270 degrees in each direction. Their relative, golden eagles, can see a rabbit from two miles away. This is astonishing eyesight!
Other daytime birds can see greater ranges of colors, including ultraviolet light. Pigeons have more cones than humans, so can see millions of different hues and are thought to be perhaps the best on our planet at detecting color.
Most snakes have two ways of seeing. Their eyes detect color quite well, but they also have a deep pocket called a pit organ that detects their prey in infrared. Chameleon's eyes can look in different directions at the same time. Frogs must pull their eyeballs in their body to blink. In the fish world, a flounder has both eyes on the same side of their body, allowing them to lie flat on the floor with both eyes looking upward.
Insects are famous for their compound eyes with many tiny parts. Some insects have up to 30,000 lenses in each eye in a honeycomb pattern. Each lens then makes up a small part of the overall picture like a jigsaw puzzle. This vision helps them in detecting movement, which comes clear to us as we try to swat a fly or mosquito! A dragonfly’s brain works so quickly that most movement they see appears to them in slow motion.
Some insects see color, although not as clearly. Butterflies can see colors better than humans while others cannot see as many. Bees see blue, green, and ultraviolet colors but do not see red.
Crab and shrimp are animals with some of the least developed vision. They have compound vision like insects, but with far less detail. Instead, they are very skilled at detecting movements, a behavior that helps them avoid predators.
Perhaps the next time we see the night-time flash of a nocturnal animal’s eyes, we’ll better appreciate how animals see the world. It amazes me that such amazing visual abilities exist in animals, and this is an exploration of only one of their senses!
The place in which we live brings continual wonder. It is this variety that adds to our days, and has added to the many articles in which I have enjoyed sharing throughout the past few years. This issue will be the last Nature Watch written by my hand. It has been great fun writing and learning with you, and I have loved every minute of it! Readers will now be able to enjoy the energy of new Museum staff who will share the wonders of the natural world. However, if you see me on out on the trail, or on the street, I hope you’ll continue to share the stories of your own adventures in our incredible north woods.
For over 44 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M. The new exhibit, The Joy of Birds: Feathers in Focus opens in May, 2011. Find us on the web at www.cablemuseum.org to learn more about our exhibits and programs. Also discover us on the web at www.cablemuseum.org, on Facebook, or at our blogspot, http://cablemuseumnaturewatch.blogspot.com/ to learn more about our exhibits and programs.