Story and Photos by Joan Herrmann
Whereiwander… one of the most amazing features of birds, mammals, and insects that truly intrigue me is their eyes. I have learned over the past forty years that some have eyes that change their color, some have unusual pupils and some even do more than observe or scrutinize. A bird’s eye color can be an indication of its age or sexual maturity or even its gender. I was surprised to learn that when a frog catches prey with its tongue and brings it back into its mouth its eyes actually help the frog to swallow the prey. The frog will blink its eyes and the eyes drop into its mouth cavity and actually push the food down its throat. While looking at the frog you can also tell its gender by its eyes. Adjacent to the frog’s eyes on both sides of its head are “round indented circles”. The circle is actually the frog’s ear, called a tympanum. If the tympanum is the same size as the frog’s eye or smaller the frog is a female. If the circle is larger than the eye then the frog is a male. I have heard people use the term “blind as a bat” which is not at all accurate. Bats have eyes and fairly good vision; however, they use their ears in the dark for echolocation to locate prey in the dark. They can see at dusk and dawn probably better than most humans.
By now most of the juvenile Bald Eagles have fledged from their nests and are fully grown. Their appearance will not resemble the mature eagle until they reach five years old. The adults have a dark brown torso and white head and tail feathers. The immatures are mostly a dark brown with white mottling or streaking. The juveniles have a brown beak and eyes that will change to yellow beak and yellow eyes when they reach their maturity. Many other birds also experience the change of eye color that is related to adulthood. The Northern Harrier also has the change of eye coloring from brown to yellow as it reaches its mature status. The Sharp-shin Hawks have a change in eye color from yellow to red and the Red-tailed Hawks change from yellow to a reddish-brown. The American Crow’s eyes change from blue or bluish-gray to brown. In addition to birds of prey, many other species of birds also experience eye color alterations; some of these birds are the Common Loon as well as Grebes, Ducks, Gulls, Woodpeckers, and Vireos. The Wood Duck male has a stunning red eye, ringed with red and the female has a dark brown eye, ringed with yellow. European Starling males and females are almost identical in coloring, but the females have a yellow ring around the edge of their iris. Most of the owls in the northeast have yellow eyes, but the Barred Owl is easily identified because of its dart brown eyes.
The expression “Eagle Eye” accurately portrays many birds, especially all the raptors (birds of prey). The Raptors must be able to see prey at great distances. They see prey at two to three times the distance that humans can as a result of their much larger eyes. For example, the human eye weighs less than one percent of the head’s weight, whereas an Eastern Screech Owl’s eye weighs about one-fourth of an ounce, which is about five percent of its entire body weight. The astonishing performance of a raptor’s eye lies more in the number of rods and cones in the bird’s eye. Bird’s eyes function like a telescope. The structure of the eye has a fairly flattened lens which is further from the retina which provides a long focal length and produces a larger image. Researchers have learned that most birds, that are active during the day, have excellent color visions, which makes sense when we see their astounding colorful plumage.
Many mammals that are nocturnal have unique eyes. The Red Fox has eyes that are similar to our domestic house cats. Their eyes have vertical oval pupils and a green reflective layer, which enhances both night and day vision. Black bears have tiny eyes compared to their body size. They have adequate vision up close, but cannot see details further than thirty feet. What they lack in eyesight, they make up for in their amazing sense of smell. They can smell a steak cooking on you barbeque grill for a distance of more than a mile away.
The compound eye of a Dragonfly contains about thirty thousand lenses. With a slight turn of its head, it has the ability to see three hundred and sixty degrees above and below. They can see in dim light as well as ultraviolet and polarized lighting. Their brain works so quickly that they see movement as if in slow motion.
Predators have eyes in the front of their faces as we do, but animals that are prey have eyes on either side of their head. Of all land-dwelling animals, horses have the largest eyes. Horses have an excellent range of binocular and monocular vision and can see everything except for what is directly in front of them, between their eyes, and a rider on their back is also a “blind spot”. Utilizing the monocular and binocular sight capabilities they have about three hundred degrees vision. This allows them to know when a predator, sneaking up from behind them.
In our area, most spiders have eight eyes. The eyes are arranged in two rows. In most spiders, the size, shape, and function is similar in all eight eyes, but the eyesight differs slightly per species. The spiders that hunt for prey, as opposed to those that create webs and wait for prey, often have larger eyes and excellent vision. Wolf spiders and Jumping spiders are two species that hunt. The Wolf spider usually hunts at night and the Jumping spider hunts during the day. Wolf spiders and others that are primarily night hunters have a reflective layer, the tapetum, at the back of their eyes. Tapetum lucidum is a layer of tissue in the eye of many vertebrates. It lies directly behind the retina, and it reflects visible light (from moonlight and starlight) back through the retina, increasing the light available to the photoreceptors. It is the tapetum lucidum that contributes to the superior night vision of nocturnal animals.
As a Professional Nature Photographer, Naturalist, and Outdoor Educator, Joan Herrmann has been teaching and doing programs for Schools, Garden Clubs, Libraries, and Nature Centers, about 38 years. After moving from the Rochester area in 1995 she began her Photography business, Essence of Nature, and also became a co-owner of The Artworks in Old Forge, New York. As a docent at Munson, Williams, Proctor Arts Institute, in Utica, New York she has been educating children and adults, for nineteen years.
In 2007 she began working with the Black River Outdoor Educational Program (BROEP) and in 2013 and 2014 did a week-long summer program at BROEP in conjunction with Mohawk Valley Community College (MVCC). Using her love of both nature and photography she created a Flora/Fauna outdoor educational program teaching students (ages 6 to 14) the joys of nature and creative photography skills.
Joan’s love of nature has been a lifelong study of Birds, Wildflowers, Mosses, Ferns, Trees, Amphibians, Reptiles, Grasses, Insects, Spiders, Tracks, Scat, and Galls. She has assisted in the cataloging of all trails used by the hiking Coaches and photographed and identified seasonal Flora.
Since October 2016 she has been writing a bimonthly nature column with Adirondack Express Newspaper. In October of 2019, she began a bi-monthly column with My Little Falls Newspaper. You may reach her at firstname.lastname@example.org