What do Deer See?
(En anglais seulement)
By: By Brian Murphy
It’s happened to nearly every deer hunter—for no apparent reason a deer spots you from a distance through heavy cover. Why? Was it your scent, your noise, your movement, or perhaps what you were wearing? While all hunters agree that deer have an amazing ability to detect movement, the consensus regarding their ability to see color is far less unanimous.
While the debate over deer vision is not new, it has intensified in recent years as more states have required hunters to wear blaze orange clothing while hunting. Many hunters are concerned that wearing blaze orange reduces their chances of success.
Another topic of debate is camouflage clothing. During the past decade, there has been a tremendous increase in the number and variety of camouflage patterns available to hunters. This has occurred despite little knowledge of what game animals actually see.
A more recent question is whether or not deer can see ultraviolet (UV) light. UV light is the type of light that causes your clothes to “glow” when near insect zappers or nightclub lights. The connection with hunting is that many laundry products and dyes used in the manufacture and care of hunting clothing contain “color brighteners” or more technically, UV “enhancers.” This is why clothes containing these products look “brighter” and “whiter” to the human eye. In fact, it has been proposed that hunters wearing UV treated clothes actually emit a “glow” that deer can see in low light conditions.
Fortunately, arguments on deer vision can largely be laid to rest due to the results of the most advanced deer vision study ever undertaken. This study revealed many previously unknown facts regarding deer vision. I was fortunate to participate in this study while working as a Wildlife Research Coordinator for The University of Georgia.
What is Vision?
Before discussing the results of the study, it is important to understand the basics of vision. First of all, what is vision? Vision occurs when light enters the eye and is absorbed by specialized cells located in the back of the eye. These cells respond to the light and send a signal to the brain which is translated into sight. The color perceived by the brain is determined by the wavelength of light reflected. In other words, objects do not actually have color they simply reflect light of a particular wavelength that our brain perceives as color. The spectrum of color ranges from ultraviolet on the short end of the spectrum to infrared on the long end of the spectrum. Humans can see the range of colors between, but not including, these two extremes.
Understanding the general make-up of the eye also is important. In all mammals, the retina, located at the back of the eye, consists of two types of light sensitive cells called rods and cones. Rods function in the absence, or near absence, of light and permit vision in darkness. Cones function in full light and permit daytime and color vision. Humans can see a wide range of colors because we have three types of cones in our eye. One is sensitive to short wavelength light (blue), one is sensitive to middle wavelength light (green) and the third is sensitive to long wavelength light (red). This three-color, or trichromatic, vision is the most advanced form of color vision known.
Differences Between a Deer’s Eye and a Human’s
Prior to our study, we reviewed the existing information on deer vision with some interesting findings. First, deer have a higher concentration of rods (nighttime cells) than humans, but a lower concentration of cones (daytime and color cells). Therefore, deer have better nighttime vision than humans but poorer daytime and color vision.
Second, deer have a pupil that opens wider than ours. This allows more light to be gathered in low light conditions. Third, deer have a reflective layer in the back of their eye called a tapetum that causes their eyes to shine at night. The tapetum acts as a mirror and reflects the light not absorbed by the receptor cells when it enters the eye the first time back across the cells for a second chance. In other words, deer get to use the same light twice while humans get to use it only once.
A fourth difference found between a deer’s eye and a human’s gives us some idea of their ability to see UV light. The human eye is protected by a filter that blocks about 99 percent of UV light from entering the eye. This filter protects our eye, much like a pair of sunglasses. It also allows us to focus more sharply on fine detail. The trade-off for having this filter is a severe loss of sensitivity to short wavelength colors, especially those in the UV spectrum.
Deer, on the other hand, do not have a UV filter. Therefore, they see much better in the UV spectrum but lack the ability to see fine detail. This explains why deer often move their head from side to side when they encounter a hunter. Since deer lack this filter, they would be expected to see a greater difference in UV treated fabrics than humans.
In August 1992, a group of leading deer researchers and vision scientists gathered at The University of Georgia (UGA) in Athens to conduct this landmark study. The group of researchers included Drs. R. Larry Marchinton and Karl V. Miller, and myself from UGA, Dr. Gerald H. Jacobs and Jess Degan from the University of California, and Dr. Jay Neitz from the Medical College of Wisconsin. This study was made possible due to a highly sophisticated computer system developed by Dr. Jacobs. This system is based on the principle that an electrical response is produced when light enters the eye. The computer interprets these responses and translates them into a “scientific best guess” of what deer can actually see.
Findings of the Study
The results of our study confirmed that deer possess two (rather than three as in humans) types of cones allowing limited color vision (Figure 1). The cone that deer lack is the “red” cone, or the one sensitive to long wavelength colors such as red and orange. This suggests that wearing bright colors while hunting does not affect hunting success. This does not mean that these colors are invisible to deer, but rather that they are perceived differently.
Deer are essentially red-green color blind like some humans. Their color vision is limited to the short (blue) and middle (green) wavelength colors. As a result, deer likely can distinguish blue from red, but not green from red, or orange from red. Therefore, it appears that hunters would be equally suited wearing green, red, or orange clothing but perhaps slightly disadvantaged wearing blue.
The results regarding the UV capabilities of deer were equally fascinating. Our results confirmed that deer lack a UV filter in their eye and that their vision in the shorter wavelengths was much better than ours. Deer also were found to have a relatively high sensitivity (good vision) in the short wavelengths where UV brighteners and dyes are active.
While not entirely conclusive, this finding suggests that deer are capable of seeing some UV light and that fabrics containing UV dyes and brighteners may be more visible to deer than to humans.
Implications for Hunters
What do the results of this study mean for hunters? Should you throw away all of your camouflage clothes? Definitely not. It is important to keep the findings of this study in perspective. There is no question that scent and movement are far more important than the color of your clothing or whether or not it contains UV brighteners.
As far as a deer’s senses are concerned, their daytime and color vision is pretty average. In fact, the actual color of the fabric is relatively unimportant as long as the pattern blends with your surroundings. Therefore, camouflage clothing is still recommended. In contrast, solid unbroken patterns, especially of light colors, are not recommended. Similarly, garments made from vinyl or plastic can alert deer because they reflect light. This works much like the glare from a blued gun barrel. It is not the color of the barrel that alerts the game, but rather the light the barrel reflects. The best of both worlds would be a product that provides both camouflage for concealment and blaze orange for safety. Such camouflage blaze orange hunting apparel is available but unfortunately is not legal in many states.
Should hunters be concerned about the UV brightness of their clothes? Perhaps. Keep in mind that this would only be problem during low light conditions such as early morning and late evening. However, this is when deer are most active. One option is to stop washing your hunting clothes in laundry products containing “brighteners.” This may prove difficult because most laundry products currently available contain these agents. However, there are now products available that eliminate UV light from clothing. Should you purchase such a product? This is difficult to answer. Hunters have been successfully harvesting deer for hundreds of years without the aid of such products. However, armed with our latest knowledge it remains possible, even likely, that such a product may help. On the other hand, it definitely can’t hurt.