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Through the Eyes of a Whitetail
By Phil Bishop, PhD.
Oct 7, 2008 – 4:51:10 PM
Through the Eyes of a Whitetail: Understanding Deer Vision
Originally printed in Deer & Deer Hunting Sept 2008
Of all deer senses, vision is the most underrated and most debated. Any experienced hunter will tell you that a mature whitetail may have trouble figuring out what you are visually, but if he gets the smallest hint of human odor, that’s the end of the story. But we may be a bit premature in dismissing deer’s visual abilities. Deer see better than many hunters have given them credit for, and they see color and ultra-violet light well enough to change my thinking about camouflage. Because this has been a debatable issue, let’s take a scientific approach.
There has been a long raging debate about whether deer see color. The simple answer seems to be yes? and no. Several years ago some deer scientists linked up with some eye experts to answer key questions about what deer really do see. They carefully dissected some deer eyeballs and did microscopic studies of eye anatomy (structure) and physiology (function). But first let’s talk about how vision works.
Those buck eyes can see you in ways you haven’t imagined. Not only can they see well but their color vision is quite different than human vision. they only see two colors.
How Our Eyes See:
Sunlight is made up of a “rainbow” of light waves with each color having a different wavelength. Colored objects absorb certain wavelengths and reflect others and we see what is reflected back to our eyes. The visible spectrum (sometimes called the optical spectrum) is the portion of light energy wavelengths that can be detected by the human eye.
There are no exact bounds to the visible spectrum; a typical human eye can detect wavelengths from about 400 to about 700 nanometers (nm) (a nanometer is 1 billionth of a meter). Ultraviolet wavelengths are at the short end of the visible light band for humans and infrared wavelengths are at the long end of the visible light band for us. For example, the color violet is at the short-wavelength of the visible light scale at 380-450 nm and red is at the long end of the scale at 620-750 nm. A blaze-orange vest (with no brighteners or dyes) primarily reflects light at about 605 nm. Dark red would be long wavelengths at near 700 nm.
The eyes of all higher animals have similar basic anatomy. Eyes are round organs with an adjustable opening (pupil) covered by a lens that can be focused.
The inside of the eye is filled with an almost-clear fluid and the inside surface is lined with the retina which contains special sensing cells, one type for low-light vision (rods) and the other type for color vision (cones). The cells are connected to an optic nerve which conveys information to the optic center of the brain where images are composed and interpreted. In humans, the very central region of the retina is specialized for high acuity vision. Among mammals, this specialization is found only in humans and other primates but not in deer.
The simplest way to interpret deer vision is to compare it to our own. Our eyes and deer eyes have basically the same parts, but there are key differences. Understanding those differences can make us better hunters.
This buck is colorblind as we describe it. The grass is yellow to a deer as is most of his world. Deer see the world in shades of yellow.
Looking Inside a Deer’s Eye:
There are several fundamental differences between deer eyes and human eyes. In general most humans are sensitive to three broad bands of light, which gives us three-color vision. A human’s color sensors are usually able to detect red, green and blue. This allows us to distinguish four basic colors: red, green, blue, and yellow. What we see as “white” is the seen as the reflection of all light waves and “black” is the absorption of all light waves.
We also distinguish as many as two million color blends giving us the ability to see many shades of different colors. Think of all the different colors of green that we can see in the deer woods in late summer. We are most sensitive to green-yellow wavelengths of light and, for equal intensities these wavelengths are seen as brightest. We don’t see the short-wavelengths (blue and violet) very well. This is why yellow is easily seen and why we can easily see the red-yellow of blaze orange, especially in contrast to the dark background of brown leaves and dark tree trunks.
Humans who are red-green color blind only see two color bands. Deer are similar to color-blind humans, and are only sensitive to two broad bands of light. Deer have one color sensor similar to our human blue sensors; the other is similar to human green sensors. But there are still some big differences between human vision and deer vision.
Deer are missing the sensors to detect red. Deer should be relatively less sensitive than we are to long-wavelength light (orange and especially red). Deer color sensors are most sensitive to short-wavelength light (blue-violet); and to middle-wavelength light (green-yellow). The relative sensitivity of deer eyes to short wavelengths (blue and violet) is high compared to humans.
So, in general, the colors that deer can see are shorter wave lengths than we see. This means that deer are much more sensitive than we are to shorter wave lengths of light (blue-violet) and less sensitive to longer wavelengths (reds). So, deer see best in the yellow, deep blue and some parts of the ultraviolet (U-V) portions of the light range.
What’s important about this difference is that deer are about eight times more sensitive than humans to color wavelengths near 430-440 nm. So what? These are the wavelengths emitted by ultra-violet (UV) brighteners (ultra-violet blue wavelengths are about 440 nm) such as those used to treat textiles (including most camouflage clothing) and those used in many clothing detergents. These UV wavelengths of light will be reflected from garments of any color from camo to blaze orange whenever brighteners are present. Light at a wavelength of 440 nm is seen as bright blue in the eyes of the deer.
And, in very low light, the deer switches to the rod vision cells (black, white, and gray) and the 440 nm light caused by the brighteners is seen by the deer as gray, and much brighter than we see it. So, the presence of blue, violet and UV components in our hunting clothes can make us stand out as both bright and colored against the natural browns, grays and greens of the woods and fields.
We don’t see the U-V and short blue colors because the lens of our eyes have yellow pigments that block about 99 percent of all UV light to protect our eyes. You can think of the filter as a pair of permanent super yellow sunglasses. The trade-off for having this protective filter is that it keeps UV light from entering our eyes, but it also makes us insensitive to short wavelength (UV) colors. Because deer lack the yellow pigment in their lens that filters out the U-V, more of the blue-violet light reaches their eyes so deer see UV well.
The blue glow coming from this hunters camo is a result of UV-brighteners in his clothes. Humans have a UV filter in their eyes, deer do not. This is what a deer sees. This pic was taken using a black-light to illuminate the brighteners in his camo.
We humans don’t see UV as color but rather as a brightening effect, especially in white or light garments, which is why clothing companies and detergent manufacturers use UV brighteners in the first place. Because trees and grass don’t reflect a lot of UV light, if our clothes do reflect a lot of UV light, we are going to stand out in the woods. If our clothing is reflecting UV light, our camouflage is more effective in hiding us from other hunters and less effective in hiding us from deer.
The specification of blaze orange requires a dominant wavelength between 595 and 605 nanometers. Deer can see this wavelength. However, the deer’s sensitivity to 605 nanometers is less than half our sensitivity. So 605-nanometer light reflected by blaze orange would be seen by deer as colored, but that color would be more yellowish-green than we see it, and less than half as bright.
Night vision scope?
Deer are outfitted with incredible night vision capability. In fact, whitetails have better night vision than we do even when we use modern night-vision optics. This is because deer have more light-detecting cells in their eyes. We humans have more color receptors for daytime vision (cones), but deer eyes have 10 times as many rod cells for black and white vision and night vision than humans.
These bucks see their world as black and white at night. Fact is they can see as well at night as we can during the daylight hours. This is due in part to the huge number of rod cells they have in their eyes.
For several hundred dollars you can buy a decent night-vision scope. Deer are born with two night vision scopes. The difference is in the physiology. Our eyes are dominated by color receptors (cones); but a deer’s, eyes have many more light receptors (rods). Rods are about 1,000 times more sensitive to light than cones. Deer’s eye cells are comprised of more than 90 percent light detection rods with only about 10 % color detecting cones giving them great low-light vision and less color sensitivity.
Another advantage for whitetails is that in low light, the pupil of the deer opens much wider than ours can, gathering about nine times more light. This is partly because whereas our pupil is round, the deer pupil is a horizontal slit that extends almost the entire width of the eye. Any small amount of light that is available is maximized by the use of internal mirrors inside the deer’s eyes.
We have all heard of the “Deer in the headlights look”, fact is, It is due to a reflective layer in the back of a deer’s eye. This layer reflects the available light across the retina twice, doubling the available light. Many animals who conduct their business at night have this adaptation.
When the light enters the eye, it hits the internal mirror and bounces the light back for another chance at detection. These mirrors are a special membrane in the eye called the tapetum. The tapetum is what makes whitetails’ eyes shine when exposed to bright lights. However, in bright sunlight a deer’s pupils contract into narrow bands. This lets a whitetail focus across a wide field of view. So while bedded, a deer can scan a broad area to detect danger.
Vision is a marvelous thing. When we walk through the woods, our heads move up and down and side to side. Our brain adjusts for our motion to stabilize the image that we see. Deer can do the same thing, but when deer really want to see clearly they stop dead still. By remaining motionless, the motion-compensation isn’t needed and vision improves.
Deer don’t see as clearly as we do for several reasons. Humans have a special spot on the retina called the fovea where a high concentration of cone cells detects fine detail. This means we have to move our eyes to maintain sharp focus. Deer eyes have a different set-up. Instead of a spot, deer have a long swath of cone cells that are only about 20% as concentrated as ours. The result is that instead of 20/20 vision, deer have about 20/100 vision.
All of us have seen deer bob their heads. This is probably because of the way the deer’s eyes are set in their head. Deer eyes are on the side of the head, which means that both eyes do not focus on the same object except for about a 65 degree overlap right in front of their nose. This limits their depth perception. That is, deer don’t see as clearly in 3-dimensions as we do.
Humans who have lost vision in one eye have the same limitation. Deer tend to see a flatter, less confusing world, so moving their heads gives them a little more depth of field. But the deer’s vision characteristics give them somewhat better motion detection and much better peripheral (side-to-side) vision than we have.
The normal human field of view reaches from about 35 degrees inward toward the nose, in each eye, to 90 degrees outward, and approximately 50 degrees above and below the horizon. To see further we have to turn our head. Contrast this with the white tail whose field of view extends about 310 degrees. This means that with a 50- degree head turn in either direction (310 +50) they can see all the way around them (360 degrees). No wonder they’re so hard to sneak up on.
Deer vision and Deer hunting:
The better we understand deer senses, the better hunters we can be. Deer do NOT see the world as we see it. They see colors much differently and they are much better equipped to see us than we are to see them.
This is a good example of how you can eliminate the blue UV-Glow in your camo or blaze orange. The hunter on the left is UV-HOT and the one on the right has treated his camo with U-V-Killer by Atsko.
Better understanding deer vision can help us be better hunters by helping us see the world from the whitetail perspective.
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