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The EYES have it

October 9, 2010
By GARRY BRANDENBURG

WHITETAIL DEER vision is uniquely adapted to this specie's needs in the survival game of life. As an avid deer hunter, I know that movement is the first thing a deer may tend to pick up on ... if their nose or ears have not already detected me in a tree-stand. So I try to move very slowly, stay silent, and I've learned long ago to hunt into the wind or hunt from stands only when the wind will blow any of my scent molecules away from the most likely approach pathways of deer.

To compare the human eye with a deer eye has lots of similarities and many subtle differences. Researchers have been trying to figure out those differences and learn more about how a deer looks at is environment. The idea that non-human mammals see only in black and white tones is an old idea that goes way back in time. How that myth got started may never be known. I suspect it was just an uneducated guess. Deer do see their world in color both day and night, just not quite within the same ranges that humans are used to. If humans could see in the dark as well as deer, we wouldn't need artificial lights.

The subject of vision is a fascinating subject in itself. Just ask any professional optometrist how many college level textbooks one could review about the eye and its visual processing systems and you would have a very tall stack of books. This very short review today is a long way from a fully detailed scientific analysis of the deer eye. So I'll summarize the high points for you.

Article Photos

TR?PHOTO?By GARRY BRANDENBURG
Whitetail deer eyes are built just right for this species, to help see well both in daytime situations and at night. The biology of the deer eye helps them survive, find foods and detect predators. Deer do have color vision, just not quite in the same ranges of the human eye.  And at night, deer can see remarkably well in sharp contrast to human eye limitations. Today’s photo was made in April 2007 from a brush pile hideout using a 300 mm lens at a distance of about 15 feet. This wild free-ranging deer did not detect me for over a minute, which allowed me to capture several images.

We humans have a round pupil that expands or contracts based on light intensity. What we look at is quickly focused to make the image sharp. To look at something different, we turn our head and/or our eyes to the new subject and the eye quickly refocuses. Deer have a more elongated horizontal pupil that allows them to see a wide portion of their horizon and all of that horizontal view is in focus. They do not have to turn their head to pick up some movement. If a movement is detected, they will turn their head to point their nose directly at the "problem" and try to decipher it a bit more.

All eyes have rods and cones, specialized receptor cells to help interpret what is being seen. Deer have three classes of photo-pigments: a short-wavelength sensitive cone mechanism, a middle-wavelength sensitive cone capability, and a short-wavelength-sensitive rod pigment. Rod cells are more numerous and better at motion detection. For deer, these cells do serve a discriminatory role in color vision, especially in low to moderate illumination levels. One benefit of this is predator-detection. Another is locating foods due to the ability to discriminate between plant species or plant parts.

Cones cells help tell the color of things. Human eyes have about 6 to 7 million cones with 64 percent for reds, 32 percent for greens and about 2 percent for blues. Deer have a different combination and number of rods and cones which allows them to see well both daytime and at night, just using different parts of the eye system to interpret the scene. They see orange and reds differently than humans and in addition are excellent in the blue to yellow-green, especially at night for the latter. Deer can see their environment at night as well as we can see our daytime environment. While darkness may place us indoors, this is just another phase of the 24 hour cycle of time for a deer.

Deer eyes cannot be moved within their sockets very much. To really look at something, they have to point their nose at it and study the situation. Still, a deer's eyes have a 310 degree field of view (without turning their heads) concerning the total peripheral zone with a 60 degree overlap created by both eyes working together looking straight ahead.

Deer eyes also have special cell layers that bounce reflected light back to the retina. Scientists call this tapetum lucidum. This is the "shine" we see at night if our car headlights strike a deer. The ability of the eye to maximize the available light at night helps them navigate, find foods and avoid predators. Now you have a new way to look at deer eyes.

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Driving at night is now adding a bit to the possibility of seeing deer when you don't want to see them. That is, of course, right in front of your grill at 55 mph! This is the time of year to drive defensively, be alert, drive slower in known deer areas and just be prepared. The saying, "Don't veer for deer" is appropriate. If a collision is imminent, just try to slow down as much as possible before impact. Tis easier said than done.

As October crops are harvested, hiding places for deer will disappear. Deer are also on the move more as the mating season draws closer during late October and early November. This is a typical time of the year for increased car/deer accidents. Be aware.

Which state has the highest probability of car/deer accidents? West Virginia comes in at 1 in 42. Iowa is second at 1 in 67. One in seventy is the odds in Michigan. Fourth is South Dakota with 1 in 76. Montana is fifth place with 1 in 82. Hawaii odds are 1 in 13,011. Alaska odds are 1 in 385. These numbers are based upon the number of licensed drivers in each state and give an indication of the probability of a deer/car accident within the next 12 months.

Deer are most active between 6 and 9 pm. If you see one, there may be others. If the first deer gets safely across the road, keep slowing down because there is a high likelihood of other deer to follow. Do not buy deer whistles for your car bumper. The money spent only supports the manufacturer of the whistle without any proven evidence that they even work at all.

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PHEASANTS FOREVER members are invited to the Oct. 16 banquet at the Central Iowa Fairgrounds. Tickets can be secured by calling 641-752-3296. PF has done a lot of good things in Marshall County from private land food and cover plots to assistance with wildlife land acquisitions. Your help through this organization is needed and appreciated. The doors open at 5:30 p.m. A great meal will await you. There will games of chance and lots of fun. Prizes will be given and of course an auction of collectable items will be offered. See you there.

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On Tuesday from 11:30 a.m. 1 p.m., the Brown Bag Bunch will meet at the GrimesFarm & Conservation Center. Bring your lunch and join naturalist Diane Pixler for an informal program. This session includes a wagon ride to the Observation Tower.

Registration is now open for the October 23 Halloween Hike at the GrimesFarm. This year's theme is "The Return of the Retaw." Discover how the misuse of a natural resource could come back to haunt us. Reservations are required for this entertaining and educational 45-minute hike. Call 752-5490 to reserve your space. All children must be accompanied by an adult.

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Garry Brandenburg is a graduate of Iowa State University with BS degree in Fish & Wildlife Biology. He is the retired director of the Marshall County Conservation Board. Contact him at PO Box 96, Albion, IA 50005.

 
 

 

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