GloucesterTimes.com, Gloucester, MA

November 7, 2012

What deer see

Outdoors Dave Sartwell
Gloucester Daily Times

---- — Deer do not have good visual acuity because their eyes lack foveae (no sharp central vision). The fovea centralis is a small pit or depression at the back of the retina forming the point of sharpest vision. It allows primates and humans, which are basically hunters, to focus intently and see very clearly when they look directly ahead at an object.

That being said, deer are much more aware of movement around them. Their eyes are located on the sides of their skull as opposed to ours which are in front. As is the case with many flight animals, their eyes bulge out a bit from the side of their face and are curved a bit more. As a result, they are able to see more than 270 degrees around them without moving their head.

This allows them to be more aware of their surroundings and movement in a wider range than humans.

For a variety of reasons, deer cannot see colors in the same way humans do. In a paper by Karl Miller, et. al., entitled “Photopigments of Whitetailed Deer”, the full range of the ability of a whitetail deer to see color was explored under research conditions.

Vision is the result of light being absorbed by photoreceptors in the retina which is the light absorbing tissue in the back of the eye. Vision is limited by the size of the eye, the size of the pupil and the refractive power of the eye’s optical elements. There are also filters the light passes through before it reaches the retina that vary by animal. In addition there is a difference in the light absorption qualities of the photoreceptors, and, the reflective tissue that lies behind the photoreceptors.

Under lab conditions, nine deer were anesthetized to measure the sensitivity of the deer’s eyes to wavelengths of light across the spectrum. The researchers came to several conclusions that help us as hunters to understand deer better.

“Deer like all other mammals have two types of photoreceptor, rods and cones.,” states the study. “The rods are responsible for vision in dim light and the cones are responsible for vision in daylight. The light absorbing properties of the rods in deer were found to be similar to those found in other mammals, including humans. Two classes of cone photoreceptor were detected in the deer. One most sensitive to short-wavelength light (blue-violet); the other most sensitive to middle-wavelength light (green-yellow).”

“The lens of the human eye contains a yellow pigment that absorbs ultraviolet light almost completely; it absorbs strongly in the violet and into the blue spectral regions. In contrast, the transmission of short wavelength light is very high for the lens of many mammals that are active at dusk, dawn and at night. The recent experiments indicate that this is true for the deer. The relative sensitivity of deer eyes to short wavelengths (blue and violet) is high compared to that of humans, as expected because deer lack yellow pigment in their lens.”

The biggest difference is that humans have three classes of cone photoreceptors while deer have only two. The three types of cones allows humans to have excellent color vision.

Unfortunately deer have only two and therefore they can see blue and yellow but they lack the ability to see the colors yellow-green, green, yellow, orange and red.

Because of the absence of red cones They are less sensitive in the spectral region that appears orange to humans and are virtually insensitive to deep reds.

With only two classes of cone photoreceptors, deer can distinguish no more than two basic colors, animals with dichromatic color vision do not see an intermediate color in the spectral region between the two colors.

That is, they do not see a color that appears bluish-yellow. Instead they see the intermediate spectral region as colorless.

The issue of how deer see blaze orange is of considerable interest to hunters and those interested in hunter safety.

Recent results lend insight into how deer may perceive blaze orange. Blaze orange is highly visible to humans because, for us, it is both intensely bright and intensely colored.

The worst news for hunters would be if blaze orange was seen by deer as intensely colored and intensely bright as it is for humans.

At the other extreme, perhaps the best news would be if blaze orange was not seen at all by the deer. Given what is known about deer vision neither of those extremes is likely to be true.

It is important to understand that a flat blaze orange garment is not an ideal camouflage.

It still stands out as colored and/or bright against dark backgrounds, against bluish-greens, pure greens, browns, tans, and grays.

As a result of this research, Dr. O’Neill, formerly of the United States Military Academy, worked out colors, textures and shapes that would be most effective for camouflage.

“The essence of digital camouflage goes back to the old question: Is the purpose of camouflage to match the background or to break up the shape of the target?” Dr. O’Neill says.

“The answer is yes — you do both. You create a micropattern that matches the ‘busyness’ of the background and makes it harder to detect the target, and you overlay it with a macropattern that makes it harder to recognize the shape of the target once you’ve detected it.

What have we learned? Deer see reasonably well, are more aware of their surroundings than we are, and see in low-light conditions fairly well.

To counteract their sense of movement, stay still in a blind or tree stand, move very slowly when stalking, and wear blaze orange that has a pattern to it to brake up the flatness of the color.