Have you ever wondered why certain animal’s eyes shine like reflectors when car lights illuminate them? Or how well nighttime species actually can see? Do animals see color the same way we do? If not, do some see in shades of just black and white? What species have the most acute vision abilities?
Early hunters quickly ascertained that deer (and other herbivores such as elk, caribou, moose, etc.) failed to see color in the same manner that humans did. A theory was then spawned by some that these animals saw their world in basic black and white. Later, as more was learned about the effects of colorblindness in humans, the idea of colorblindness in these animals became a more realistic solution to their inability to spot unnatural colors amidst natural ones. But no one could prove exactly what colors failed to be detected, or what colors they appeared to be to the animals. However, thanks to extensive research and new technology, we’re beginning to see how deer and other animals view their world.
“Ophthalmology” is the branch of medicine concerned with the eye and its diseases. Thanks to the research in this field, we now understand far more about how our human vision works. This same technology has also resulted in increasingly understanding how animals’ eyesight works, and what they see when compared to human eyesight. This branch is known as “veterinary ophthalmology” and it goes a long way toward explaining how animals view their world.
Deer, for example, have only two types of cones in their eyes and are termed “dichromatics,” or having the ability to sense two colors of light – blue and green. Man has three and is a “trichromatic” species and is thus able to see all three primary colors – red, green and blue – and the various combinations of the three. Cones are also useful to detect stationary objects and for vision in bright light. Deer do not interpret colors in the same manner humans do, but have sensitivities to blue and green colors. Determination of various shades of green may be useful in identification of edible plants. However, deer’s inability to see red is why an immobile hunter dressed in red or hunter orange isn't obvious in the eyes of a deer.
Why do deer and some other animals' eyes shine at night? It’s a part of their eyes called the tapetum. The tapetum is a reflective layer of tissue just behind the retina. After light strikes the retina, any that is not absorbed will pass through the retina and contact the tapetum. The tapetum serves as a mirror to reflect light back onto the retina, giving the retina a second chance. The tapetum allows low levels of light to be magnified and also acts like a roadside reflector when bright light strikes it.
The retina of nocturnal predators, however, is almost entirely composed of rods. The other type of vision cells, cones, is absent or almost absent, leaving them with virtually no color vision. The photosensitive pigment inside the rods, rhodopsin, is particularly sensitive to low levels of light. At night, in the rod-rich eyes of dark-adapted animals, rhodopsin is created faster than it breaks down. Therefore, the threshold of light needed to stimulate the eye and create good vision is reduced.
Most nocturnal predators are largely inactive during the day to avoid over-stimulating their highly sensitive eyes, but do have specialized pupils to shut out damaging bright light. Their pupils are usually circular or vertical slits, which is the most effective for allowing light into the eye when their pupils dilate to their maximum at night. The circular pupil is not that efficient at blocking light, but the vertical slit is. The slit pupil can shut out all light except a narrow band.
Large eyes, with a wider pupil, larger lens and increased retinal surface can collect more ambient light. For example, an owl's eyes fill over one half its skull. Likewise, some species have evolved tubular eyes. By expanding the eyes in this way, they are tightly fit in the socket. Because of this feature, many nocturnal animals can’t move their eyes within the orbit. Instead, they have extraordinary rotational ability in their neck. Owls, for example, can rotate their neck a full 270 degrees.
Terms such as “eyes like an eagle” or “hawkeye” refer to a person with extremely keen eyesight, and they have a solid base for fact. Many species of raptors boast eyesight many times more efficient than humans. Raptors have front facing eyes. This makes possible a binocular vision similar to our own. In binocular vision, the fields of view of the left and right eye overlap. Animals with eyes on the sides of their head (such as fish or rodents) have low binocularity (what each eye sees overlaps very little) but high periscopy (each eye has a wide field of view). The right-eye and left-eye visual fields of a hawk overlap about 90 degrees. A further adaptation in raptors is the cornea and lens are angled toward the beak to increase the overlapping region even more.
Binocularity allows for stereoscopic vision, which in turn allows for determination of distance. A stereoscopic species views the slightly different images from the right and left eye, and then its brain automatically determines the distance to the object. Raptors, with their greater amount of visual field overlap, have the greatest abilities to use binocularity to develop a sharp, three-dimensional image of a large portion of their view.
Another unique structure in a bird's eye is the pecten. Pecten is a thin, greatly folded tissue extending from the retina to the lens. Predatory birds such as eagles and hawks have the largest and most elaborate pecten of all the birds. The pecten supplies nutrients and oxygen throughout the eye, thereby reducing the number of blood vessels in the retina. With fewer blood vessels to scatter light coming into the eye, raptor vision has evolved to be the sharpest vision known among all organisms.
One thing all wild creatures do detect very quickly is movement. So regardless of the species you encounter, if you don't want them to spook, worry less about what colors you’re wearing and more about not moving. And keep a sharp eye out because they sure do.

Antler Collection At Fair
Visitors at the Chenango County Fair on Saturday should make a point to visit the Conservation Area. The entire year-by-year collection of shed antlers from the “Charlie Buck” – a popular trophy whitetail that lived out its life within the fenced area of the Cortland Waterworks – will be on display.