Deer Vision

By Robert J. Korpella

First posted on 12-03-2010

Even perched in a tree stand, I’ve been found by deer. If the wind is blowing, just slightly, from my direction to theirs, I never stand a chance. But often times, deer have looked directly at me when I know they can’t pick up my scent. They sense something is wrong and start to jerk their heads side to side, trying to get a better view. Does often paw the ground as I sit as motionless as possible.

At times, those deer moved on at a walk, maybe in quick, short runs, sometimes snorting as they went. On other occasions, the deer simply went back to feeding and ignored me. But why the difference in behavior? Wildlife biologists who have studied deer vision have come up with some interesting finds.

Eyes project images onto the retina, which is composed of cells called rods and others called cones. Rods provide contrast in low-light situations, like night driving for humans. Cones help animals distinguish colors and details.

Humans have three types of cones that allow perception of colors from low-wavelength blues to high-wavelength reds as well as the medium-wavelength greens in between. Deer are limited to two types of cones, lacking the ones that distinguish reds and oranges. It doesn’t mean that anything in that color range disappears from a deer’s view, it only means deer process those colors differently than humans. Bees, for example, cannot see red. To a bee, a red flower looks the same as a black one.

So, to a deer, a blaze-orange hunting vest might just blend in with the scenery, or at least be more difficult to distinguish because the color is not perceived, so it doesn’t stand out. But, a denim jacket might look like an unexpected blue patch in a tree or on the ground, and give deer something to worry about.

Researchers at the University of Georgia have looked at the concentration of cones in human eyes versus those in deer. Human eyes have a high concentration of cones, allowing us to discern a great deal of detail in objects. Deer, do not have as high a concentration and are likely to see at a 20/200 vision level. That means a deer sees at 20 feet away what a human sees at 200 feet, which makes a deer legally blind in human terms.

The way the rods line up in a deer’s eye gives them more detail perception in a horizontal section in the middle of their field of view. That would be similar to looking at a photograph where the subject is in crisp detail in the center of the image, but the background is blurry because the photographer adjusted his aperture setting to concentrate on the center of the image.

So, if I wore a blaze-orange shirt and moved very slowly to pick up my camera when a deer looked in my direction, I would stand less of a chance of disturbing the deer than if I was motionless but wearing a blue shirt.

To add one more interesting angle to the mix, researchers believe deer may be able to see light in the ultraviolet range. The theory has yet to be proven, but it is based on the idea that humans have special pigments in the eye to block UV rays because we are a species that live long lives. Without the pigment, our eyes would fail us too early in the ageing process. A deer, however, lives a comparably short life with no need to be concerned about UV light.

Most laundry detergents today advertise how bright they make colors and whites. The reason is UV brightener additives. Color aside, that blaze-orange jacket might just glow in the dark – or in the light – to a deer’s eyes.