The Science of Deer Vision
Does wearing orange reduce your chance of hunting success?
Photo courtesy Savannah River Site via flickr
It’s happened to every bowhunter—a deer spots you for no apparent reason while perfectly concealed. 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 what colors deer can see is far less unanimous. Because of this, many hunters, especially bowhunters, 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 rapid growth 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 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. 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. It has been proposed that hunters wearing UV-treated clothes actually “glow” to deer.
Fortunately, many of these arguments can be laid to rest due to the results of several studies conducted since the early 1990s. I was fortunate to participate in the first and most important of these studies in 1992 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, 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 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. 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 allow only black and white vision. 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 cone photopigments (specialized photoreceptor cells) 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 basic differences between a deer’s eye and a human’s eye 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 much 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 light not absorbed by the receptor cells when it enters the eye the first time back across the cells for a second chance. In essence, deer get to use the same light twice while humans get to use it only once.
In August 1992, a group of leading deer researchers and vision scientists gathered at the University of Georgia to conduct this landmark study. The group 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 that interprets electrical responses produced by the eye and translates them into a “scientific best guess” of what deer can actually see.
Our study confirmed that deer possess two (rather than three as in humans) types of cone photopigments allowing limited color vision (Figure 1). The cone photopigment deer lack is the “red” cone, or the one sensitive to long wavelength colors such as red and orange. These colors are invisible to deer, but rather 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 disadvantaged wearing blue.
The results regarding the UV capabilities of deer were equally fascinating. Our results confirmed that, unlike humans, deer lack a UV filter in their eye. In humans, this filter blocks about 99 percent of damaging UV light from entering the eye. It also functions much like a pair of yellow shooting glasses and allows us to focus more sharply on fine detail. The trade-off is a loss of sensitivity to short wavelength colors, especially in the UV spectrum. Because deer do not have a UV filter, they see much better in the UV spectrum but lack the ability to see fine detail. This helps explain why deer often move their head from side to side when they encounter a hunter.
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 should be avoided because they reflect light much like the glare from a gun barrel.
Should hunters be concerned about the UV brightness of their clothes? Perhaps. One option is to stop washing your hunting clothes in laundry products containing “brighteners.” This may prove difficult because most products contain these agents. However, there are products available that eliminate UV light from clothing. Should you purchase such a product? This is difficult to answer. Hunters have successfully harvested deer for hundreds of years without the aid of such products. However, armed with our latest knowledge it remains possible that such a product may help. On the other hand, it definitely can’t hurt.
Brian Murphy is a wildlife biologist and CEO of the Quality Deer Management Association (www.QDMA.com). He also has been an avid bowhunter for the past 30 years.