Aging Whitetails: How Close Is Close Enough?
September 22, 2010
"Boy, that buck looks like an oldtimer. I wonder how old he is?"
Many of us have asked that question over the years. For starters, we're a curious lot, but recently the question has become more than one of passing fancy. Today, more than ever, it requires an answer. Age is a key ingredient, whether you're managing the herd or trying to satisfy the curiosity of a fortunate hunter.
I found my own curiosity piqued earlier this year, after taking a buck that was clearly older than the norm. The big 8-pointer had well-worn, dark-stained teeth with a muzzle that was mostly gray, so I decided to have him aged. I also had the jawbone from a mature 10-pointer I'd shot in 2001, and I wanted to find out about him as well.
There are several ways to age whitetails. The most familiar technique, and the one most used by the public, is called the eruption-wear or wear-and-replacement method
We've all seen photos of deer jawbones 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 patterns of deer of known age.
Another technique, perhaps not as well known to whitetail hunters, is called the cementum-annuli method. The idea here is to process the incisor tooth of a whitetail through a series of scientific steps, then view it under a microscope. When properly prepared, the rings of growth can be counted to determine the age of a deer, much as we can age a tree by its rings.
To have my two deer aged, I traveled to the Rose Lake Research Laboratory, a Michigan Department of Natural Resources facility just northeast of Lansing. There, the cementum-annuli program is one of the areas of animal research administered by wildlife scientist Paul Friederich. In addition to aging whitetails, the lab also ages bears, otters, fishers, elk, bobcats, martins, badgers, foxes, coyotes and wolves for research and management purposes.
I was invited to join Paul and lab technicians Kristine Brown and Melinda Cosgrove as they guided me through the multiple steps required to age wild animals. The first of those steps, as you might guess, is the removal of the tooth.
"For whitetails, we need the central incisors, which are the teeth at the bottom front of a deer's jaw," Paul said. "The two in the middle work best."
The incisors are easily removed while the deer is still 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," Paul told me.
After the excess tissue is removed, the tooth is then placed in a small bag and delivered to the lab. There, the first step is to de-calcify (soften) the tooth by soaking it in a weak acid solution. As this is done, the tooth grows rubbery, like a pencil eraser.
The tooth is frozen for next ease of cutting and then placed in a cryostat. This is a machine that slices the tooth so thinly the resulting slices are measured in microns. The thin slices of tooth are, in turn, placed on a slide for viewing under a microscope.
Kristine arranged the wafer-thin tooth slices on a slide, and then added a solution containing methanol, glycerin and giesma stain to enhance them for viewing. A second glass slide was placed on top, and the slender tooth slices moved to a microscope.
Now the rings in most teeth will be clearly visible, and they can be counted in much the same fashion as rings in a tree. Each ring represents what scientists believe was a period of stress during the deer's life. Maybe it's the animal's response in preparation for the hardship of oncoming winter or the stresses of breeding season. Researchers aren't exactly sure why the rings form, but they do know that they form at very regular intervals, and that's obviously the key to using them for aging specimens.
"Most teeth are very easy to read, but occasionally I will see some 'noise' in a tissue sample," Paul noted. ("Noise" is a term for a line of a ring that isn't distinct.) If there is enough noise in a tooth, it can create an error in aging. However, that doesn't happen often with the cementum-annuli method. On whitetails, I would say our aging estimates are correct more than 85 percent of time."
How does the accuracy of this method of aging a deer compare to that of eruption-wear?
"Visual (eruption-wear) aging of deer is more cost-effective, but the problem is the difficulty encountered when trying to age older deer by tooth wear," claims Jim Hammill, owner of Iron Range Consulting and Services and a retired biologist with a great deal of experience in the tooth-eruption technique from more than 30 years of DNR service. "After a deer reaches three years, it's tough to accurately age. The percentages (of correct answers) drop precipitously, even for trained biologists."
This is backed up by a Montana study done to evaluate the accuracy of aging ungulates. Six biologists -- two from the state of Washington and four from Montana -- aged 126 known-age whitetails. (The study also included elk and mulies, but we'll look only at the whitetail data.)
Of the whitetails 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 1/2- and 3 1/2-year-olds were well represented, at 76.1 percent (96 of 126 deer). Of the 2 1/2s and 3 1/2s, the percentage correctly aged was 48.9 (47 of 96 deer), with some estimates off as far as three years.
How did counting the rings fare? In another study of 74 known-age whitetails ranging up to 9 1/2 years old, 63 (just over 85 percent) were aged to the right year. Most of the incorrect estimates were off by only one year.
WHAT SOME EXPERTS SAY
Granted, these are limited samplings, but with the money being spent on land purchase, habitat development and hunting gear today, is it worthwhile for serious managers and hunters to send deer teeth to a lab for aging?
Experts disagree as to how close is close enough when aging deer. It depends on your goals. Texan Dr. James C. Kroll, director of the Institute for White-tailed Deer Management & Research and a longtime contributor to this magazine, says being able to lump deer into rough age-classes is adequate in most management situations.
In James' view, most of us don't need to be able to do more than place deer into the following categories: fawns; yearlings (1 1/2 years); (2 1/2 through 4 1/2 years), mature (5 1/2 to 6 1/2 years) and overly mature (7 1/2 years-plus). James says a person who learns the eruption-wear method can do a good job of placing deer into these age-classes.
Some others think that in their situations, it helps to be more accurate. Among them is Colby "Skipper" Bettis, manager of Legends Ranch in Big Rapids, Michigan. He says he feels the cementum-annuli method produces the best results.
"It may be for a Southern deer manager that the wear technique is okay, but some of those ranches feed their deer year around with pellets," Skipper says. "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."
He claims the success he's experienced is outstanding.
"We tag some of our fawns, so we know exactly how old they are," Skipper notes. "We send the teeth from a hundred deer or so a year and have been doing so since the late '80s. We also send the teeth of the deer that are tagged, but we don't give the lab that information. This year their numbers were lower than we'd like, but up and until this year the lab was right on 99 out of a 100 on aging our tagged deer."
Getting an exact age on deer might be important to some professional whitetail managers, but what about for the rest of us? Remember the two bucks I had aged? Well, a month or so later the results came in. The 2001 buck was 5 1/2 years old. And the one from 2002? The gray-chinned oldster didn't have the rack of the first one (a score of about 120, versus 153), but he might well have been his daddy. He turned out to be 9 1/2!
When I learned how old that buck was, I smiled. I couldn't help but wonder what he'd seen as a juvenile, as a mature buck in full blossom and finally, as an old-timer. I felt honored to have harvested such a distinguished gentleman.
Having a deer aged can be done for the fun of satisfying your curiosity and adding to your memory of a special deer. It also can be quite useful in managing a herd. But while counting rings is more accurate than comparing tooth wear, it isn't needed in every hunting/management situation.
FOR YOUR INFORMATION
If you're interested in learning more about aging by the cementum-annuli method or want to arrange for testing of your own deer's teeth, visit whitetaildeer-bullseye.com.