July 14, 2022
Back in college, my wildlife professor had us take a quiz on aging 10 deer jawbones. We were using a technique developed in 1949 by deer researcher Bill Severinghaus from New York, based on tooth wear and eruption. To this day, this method has been the standard in aging deer for all wildlife biologists, and I was very proud to see an “A+” on my quiz.
Aging deer has become somewhat of an obsession for many hunters. How cool is it when you know the exact age of your buck! One of my all-time favorite bucks only scored in the low 150s, but he was 9½ years old. Obviously, having a deer live this long, let alone being fortunate enough to tip him over, is something I’ll most likely never get to experience again.
Although all wildlife students and professional deer biologists are familiar with the tooth replacement and wear technique developed by Severinghaus, through the years, various research papers started to question the accuracy of this aging technique. The initial study only used a small sample size of 26 known-aged deer between 2½ and 10½-plus years old. This is not a slam on the classic research, but as you can imagine, getting a sample size of known-aged deer in 1949 had to be very difficult. In fact, even today, an adequate sample size of known-aged deer is still challenging.
Although still not proven, more questions concerning the accuracy of Severinghaus’s method started to emerge concerning tooth-wear difference as it pertained to various soil types. For example, the teeth of a deer that lives in a silty loam soil may not wear as fast as the teeth of a deer living in a sandy environment. Additionally, there may be differences in wear due to variations in nutrition (good versus bad), or what was found in mule deer — does tended to be incorrectly aged more often than bucks.
Through the years, various research papers have concluded that deer older than 3½ were extremely variable and showed no consistent pattern of wear using the Severinghaus method. They further determined that many biologists would under-age older deer and over-age, younger deer.
Then, in the 1970s, researchers started to compare the jawbones of known-aged deer with the cementum annuli method. The latter is the process where you count the dark rings of cementum (like the growth rings in a tree), which is in the root of a deer’s lower front teeth. Cementum rings tend to coincide with seasons; appearing dark and thin during winter, when resources are scarce, and light and thick during spring and summer, when resources are more abundant. This annual layer of cementum on the tooth makes aging possible.
Although not 100% accurate, this is still the most precise way of aging deer (or other critters). The advantage of using the Severinghaus method is that it can be used in the field, whereas the cementum annuli method requires laboratory analysis and costs roughly $33 per deer.
Another potential bias in many of the previous aging studies is they were conducted with known-aged, deer raised in pens. As you can imagine, acquiring a data set of known-aged, free-ranging deer can be a daunting challenge.
In 2002, biologist Ken Gee presented data on 432 deer collected from the Noble Foundation Wildlife Unit in Oklahoma from 1983–1997. These deer were captured as fawns using a drop-net and marked with either an ear tag or a tattoo. Although Gee was trying to compare or modify the Severinghaus model, he also found inconsistencies throughout. He concluded that aging deer 3½ years or older was simply too variable to classify into a specific age class.
Last year, I drew an Iowa deer tag and had the opportunity to hunt on land managed by wildlife biologist Dr. Mickey Hellickson, owner of Orion Wildlife Management Services. While hunting, I came across some of Hellickson’s raw data on deer they’d harvested on the ranch. Hellickson compared a total of 228 jawbones from bucks and does taken off his properties in Iowa, and compared the tooth replacement and wear results with the cementum annuli process.
Hellickson’s rough data indicated the tooth replacement wear method developed by Severinghaus was only accurate 18% of the time. The cementum annuli method indicated the majority of jawbones were one year older than the tooth replacement and wear methodology had shown. Additionally, 51% of Hellickson’s jawbones were classified as one year older using the cementum annuli process, while 23% were two years older, and 8% were three years or older.
I shared this data with the National Deer Association’s Chief Conservation Officer, wildlife biologist Kip Adams, and he said, “I’ve heard of these discrepancies before, and it may occur more in the Midwest and South.”
My question back to Adams was, “If this is true, just how far geographically does this disconnect between Severinghaus’s tooth replacement and wear method exist?” As of this date, no biologist knows.
Having an idea of the age of the bucks in your area can be a valuable tool in determining which bucks to tip over, and which ones to pass. Although this column may seem to rock the boat on aging deer, the good news is state deer biologists only need to know three age classes — fawn, yearling, and adult — of deer when they create population-reconstruction models.
As for hunters, I’d suggest aging your deer with the Severinghaus method up to 2½ years of age. For anything 3½ years old or older, I recommend sending in your deer’s bottom front teeth to Wildlife Analytical Laboratories. For a nominal fee, they can perform the cementum annuli technique and accurately age your deer. Just like people, through the years I’ve seen deer with missing or extra molars on the side of the jaw; one jawbone had its first molar growing perpendicular to the jawbone.
Although rare, some whitetails (generally in the South) even possess upper canines. Variability can also include deer wearing down the teeth on one side more so than the other. The result is two different age classes within the same jawbone. Additionally, biologists have also suggested that sex biases and nutrition (or lack thereof) can have significant impacts on tooth wear, as will soil make up, particularly in areas with especially sandy soil.