By Rick Asmus, “North American Whitetail’ October 2003
“How Old is that Deer?”
Hunters have asked that question frequently over the years. We are a curious lot, but recently the question has become more than one of passing fancy. It requires an answer in today’s deer-world more than ever before. Age is a most important ingredient whether managing for a healthy whitetail population or to answer the curiosity of a fortunate hunter. Often times trophy deer are measured by the amount of antler they are carrying, but for some, a buck or doe that has survived many deer seasons can make for a special kind of trophy magic.
A certain wonder of what an older deer has encountered to become the master of his domain and still continue on to older age. I found my curiosity piqued last year after harvesting a buck that was clearly older. The big eight-pointer had dark stained teeth that were well worn, with a muzzle that was mostly gray. I decided to have him aged. I also had the jawbone from a mature 10 pointer I had taken in 2001. I wanted to find out about him as well.
There are several ways to age whitetails. The most familiar technique is called eruption-wear. We have all seen the pictures of deer jaws with worn molars. This method is used to judge the amount of wear on the molar teeth of a whitetail by comparing it to the wear of other known age animals. Another technique, perhaps not as well known to whitetail hunters, is called the cementum-annuli method. The idea here is to process the incisor of a whitetail through a series of scientific steps and then view it under a microscope. When properly prepared the rings of growth can be counted to determine the age of a deer, much the same as the rings of a tree.
To have the deer aged I traveled to the Rose Lake Research Lab. It is a Michigan Department of Natural Resources facility located just Northeast of Lansing. The cementum-annuli program is one of the areas of animal research administered by wildlife scientist Paul Friederich. In addition to ageing whitetails the lab also ages bear, otter, fishers, elk, bobcat, martin, badger, fox, coyotes and wolves.
I was invited to join him and lab technicians Kristine Brown and Melinda Cosgrove, as they guided me through the multiple steps required to age wild animals.
The first step is the removal of the tooth.
“For whitetails we need the central incisors which are the teeth at the bottom front of a deers jaw. The two in the middle work best, though we can use pre-molars also, Paul noted. The teeth are easily removed when the kill is fresh. “Just take a knife and make a slice down either side of the tooth and at the bottom where the root lies then gently remove it being very careful not to break-off the root tip”, he added.
The tooth is then placed in a small bag and delivered to the lab.
The first step at the lab is to de-calcify (soften) the teeth by soaking them in a weak acid solution. A tooth becomes very rubbery like the eraser on the end of a pencil. The teeth are then frozen for ease of cutting and placed in a cryostat. A cryostat is a machine that slices the teeth to a thickness measured in microns. These thin slices of tooth are in turn placed on a slide.
“Setting the slices on slides is part art and part science”, said Kristine as she cut and arranged a half-a-dozen pieces on a slide. She added a solution containing methanol, glycerin and giesma stain to die the wafer thin slices of tooth and enhance them for viewing. A second glass slide is placed on top and the slender tooth slices are moved to a microscope for viewing. At this point the rings for most teeth will be clearly visible and may be counted. Each ring represents what scientists believe to be a ring of stress. Perhaps it is the animal’s response in preparation for the hardship of an oncoming winter or for the stresses of the breeding season. They aren’t exactly sure why the rings form, but they do know that they form at very regular intervals. “Most teeth are very easy to read but occasionally I will see some noise in a tissue sample”, said Paul.
Noise is a word for a line of a ring that is not distinct. If there is enough noise in a tooth it may create an error in ageing but that doesn’t happen often with the cementum-annuli method.
“On whitetails I would say our ageing estimates are correct more than 85 percent of time”, said Friederich.
Eruption Wear vs. Cementum Annuli
How does the accuracy of using the cementum-annuli method of ageing a deer compare to that of eruption-wear?
Jim Hammill is the owner of Iron Range Consulting and Services and a retired wildlife biologist for Michigan’s Department of Natural Resources. He has had a great deal of experience in the tooth-eruption technique in over 30 years of DNR service. “Visual ageing of deer is the most cost effective method. The problem is the difficulty encountered when trying to age older deer by tooth wear. After a deer reaches 3 years its tough to accurately age, the percentages drop precipitously even for trained biologists”. This fact is made clearer in a Montana study. The study was designed for evaluating the accuracy of ageing Montana ungulates, comparing the eruption-wear method vs. cementum-annuli technique. Six biologists, 2 from the state of Washington and 4 from Montana participated in ageing 126 known age whitetails. The study included elk, mule deer and whitetail deer but for the purposes of this article we will look only at whitetail data. Of 126 whitetails that were evaluated by the eruption-wear technique, 42.9 percent (54 of 126) were aged correctly. There were no fawns in the study group but 2 and 3 year olds were well represented with 76.1 percent (96 of 126). Of two and three year olds the percentage correctly aged was 48.9 percent (47 of 96) with some estimates off by as much as 3 years.
How did counting the rings fare? In another study of 74 known age whitetails, ranging up to 9 years old, 63 were aged correctly. That’s just over 85 percent with most of the incorrect estimates off by one year. These are limited samplings but with the money being spent on land purchase, habitat development and hunting equipment is it worth the while of serious managers and hunters to send the teeth off to the lab for ageing?
Experts disagree on how close is close enough when ageing deer. Dr. James Kroll, wildlife biologist and whitetail manager from Texas believes that being able to identify a deer as fawns, yearlings, which are obvious, (3 and 4 years), mature (5-6 years) and over mature 7 years and up is adequate for management purposes. All are aged using the eruption wear method. Yet others feel it is very important to have greater age accuracy. For Colby Bettis (Skipper), manager of The Legends Ranch in Big Rapids Michigan accurate ageing is very important and he feels that the cementum-annuli method produces the best results. “It may be for some southern deer manager that the wear technique is OK but some of those ranch’s feed their deer year around with pellets. It gives their deer a definite tooth wear pattern. We like to be as natural as possible so our deer eat what is available to them. Tooth wear isn’t always the same, that’s why cross-sectioning the teeth gives us the best results”, cites Colby. The success he has experienced is outstanding. “We tag some of our fawns so we know exactly how old they are. We send the teeth from a hundred deer or so a year and have been doing so since the late 80’s. We also send the teeth of the deer that are tagged but don’t give the lab that information. This year their numbers were lower than we like but up and until this year the lab was right on 99 out of a 100 on ageing our tagged deer.
Aging deer is part of a very important business for whitetail managers but how about the rest of us?
Remember the two bucks I took in to be aged? Well a month or so later the results came in. The 2001 buck turned out to be 5 ½ years old. A great buck that was in the prime of life. The 2002 buck? The gray-chinned oldster wasn’t carrying the head-gear of the first buck (about 120 inches compared to 153 inches), but he may well have been his granddaddy, because he was a whopping 9 ½ years old. When I learned how old he was I started to smile, what a trophy! Thoughts of what he must have seen as a juvenile, as a mature buck in full blossom and finally as an older deer. What would the tape have measured had he been prime at 5 ½ or 6 ½ years of age? I felt a certain honor in harvesting such a distinguished gentleman.
Having a deer aged can be for the fun of satisfying your curiosity or useful as a tool in a hunters bag. Though counting the rings is more accurate than comparing tooth wear it is not needed in every hunting and management situation. It is however a way to make for a very special hunting memory.