September 17, 2019

How Old Is That Big Buck You Just Bagged?

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We like to take a guess at the age of any deer we see and more importantly, the ones we shoot. And how do you guess the age of a deer? Some think they can do it by “sizing them up”, in other words, if they deer looks mature, coloring, antler size, etc. The method most used for many years is to yank open the deer’s mouth and take a gander at the deers molars. In this, we are looking for wearing. The logical conclusion is that the more a deer’s molars are worn off, the older they are. This is generally a true statement but it seems that this method may not be the most accurate way to age a deer.

The other day I received and email from Henry Chidgey of Wildlife Analytical Laboratories in Burnet, Texas. Henry works for a company that specializes in aging of deer. He thought readers would be interested in learning about other methods of determining the age of deer, how it is done, why it is important, etc. Henry sent several pages of information that he wanted to share.

The first might answer the question of why you might want to know the exact age of your deer.

Why do people care how old their harvested deer (or other mammal) is?

The best way we know to answer this is by way of an analogy. If you were a master gardener and your passion was growing tomatoes you might have as an objective raising the largest, most beautiful tomatoes you could. In addition to genetics and nutrition (soil, fertilizer and water) you would want to learn the right time to pick or harvest these tomatoes. You wouldn’t want to pick them too early or too late. Experience of picking too early & too late, over time, would allow you to do a better job at maximizing your goal—having the largest, most beautiful tomatoes you could.

Whitetail deer hunters and managers have goals for bucks that are very similar to these master gardeners. They want to have the bucks they harvest achieve their maximum potential. In a whitetail that usually occurs when they are 5-6 years old. They want feedback on the deer that they harvest about how good their judgment was this time, so that they can learn and improve
their skills at judging age before they squeeze the trigger or let loose of the arrow. Another reason for wanting to know the age of harvested mammals is to collect data that enables correlation between habitat and the health of the mammals in that habitat. Body weight vs. age is a great indicator over time of changes in habitat conditions either good or bad.

The second bit of information is what biologists have to say about aging deer and other mammals.

What do Biologists and Their Studies Say About How to Age Deer and Other Mammals?

In the Journal of Wildlife Management 64(2):441-449 Kenneth Hamlin and 4 other wildlife professionals from the Montana Fish, Wildlife, and Parks concluded (based on a study of 53 known age mule deer and 21 known age whitetail by eruption-wear and 108 known age mule deer and 74 known age whitetail by cementum annuli) “The accuracy provided by the cementum annuli method is necessary to determine whether various physical and population parameters change significantly with age of the animal…. Ages assigned by eruption–wear criteria were not reliable for comparing physical measurements and population parameters by age among populations…. Accuracy for a sample of known-age mandibles aged by eruption-wear criteria was 62.3% for mule deer, 42.9% for whitetails, and 36% for elk”. “The accuracy for individual biologists ranged from 54.7-71.7% for mule deer and 23.8-66.7% for whitetail deer” “This aging was done by 4 biologists from Montana and 2 from Washington considered to be experienced in aging deer used eruption-wear to age these mandibles…”. Cementum annuli aging yielded a 92.6% accuracy rate for mule deer (with no error over 1 year), 85.1% accuracy rate for whitetails (only 2 in error over 1 year) and 97.3% accuracy rate for elk.

Ken Gee, a wildlife biologist at the 2,947 acre Noble Foundation Wildlife Unit (NFWU) said at the conclusion of a study he did in 1996 “These results indicate that this widely used technique (sic eruption-wear) is very inaccurate for classifying adult deer into specific year age-classes on the NFWU….(it)only allows us to confidently place deer into three age classes: fawn, yearling, and adult.” The study was done using “34 practicing, established, well respected deer biologists from the southeastern U.S.

Here is a list and answers to frequently asked questions.

FREQUENTLY ASKED QUESTIONS

What is Cementum Annuli aging?

The basis for cementum aging is the cyclic nature of cementum deposits on the roots of mammals’ teeth each year, which results in a pattern of “rings” in the tooth, like those formed in the wood of trees. A darkly staining ring, or “annulus”, is formed during winter on most all mammals. Abundant, lightly staining cementum is formed during the growth seasons of spring and summer. Some “experts” say these rings occur because of nutritional or seasonal stress, but since the same rings occur on human teeth, we doubt that is true.

Why do people care how old their harvested deer (or other mammal) is? Mostly asked by our non hunter friends.

The best way we know to answer this is by way of an analogy. If you were a master gardener and your passion was growing tomatoes you might have as an objective raising the largest, most beautiful tomatoes you could. In addition to genetics and nutrition (soil, fertilizer and water) you would want to learn the right time to pick or harvest these tomatoes. You wouldn’t want to pick them too early or too late. Experience of picking too early & too late, over time, would allow you to do a better job at maximizing your goal—having the largest, most beautiful tomatoes you could.

Whitetail deer hunters and managers have goals for bucks that are very similar to these master gardeners. They want to have the bucks they harvest achieve their maximum potential. In a whitetail that usually occurs when they are 5-6 years old. They want feedback on the deer that they harvest about how good their judgment was this time, so that they can learn and improve
their skills at judging age before they squeeze the trigger or let loose of the arrow. Another reason for wanting to know the age of harvested mammals is to collect data that enables correlation between habitat and the health of the mammals in that habitat. Body weight vs. age is a great indicator over time of changes in habitat conditions either good or bad.

How does cementum-annuli compare to that of eruption-wear?

The eruption-wear technique of aging ungulates compares the tooth wear of known age animals to the tooth wear of harvested animals. The theory is that you should be able to determine age by finding a match, wear wise, with a known age specimen. I think the cold hard facts show that this is just guesswork, especially for deer 2 ½ years or older. Simply spoken, eruption wear does not work if you want an accurate age of the animal you harvested.

The cementum-annuli (cross-sectioning teeth) method of aging deer, elk and other wild animals is much different. It first requires decalcifying the central lower incisors and then cutting crosssections of the root tips to a thinness measured in microns. The slice of tooth is then placed on a slide and a special dye is added to enhance viewing. It is placed under a microscope. Circular
lines within the tooth’s diameter are readily visible and can be counted much like the rings of growth on a tree, indicating a deer’s age. The question is, how effective are each of these methods for aging deer and other ungulates?

And finally, an explanation of what cementum annuli is.

What is Cementum Annuli?

Would I know them if they walked up and said hello?

• Every year any mammal has a tooth in their jaw there is a layer
of cementum deposited around the root, under the gum line

• Annuli just means ring or rings in Latin

• A root of a mammal’s tooth ends up being very much like the
rings on a tree

• Science is not sure why it occurs, but it does

• Probably does not occur because of nutritional or seasonal
stress (because the human mammal exhibits the same
phenomena)

• Compared to other methods of aging is very accurate (but not
perfect)

• Studies show accuracy rate at 85% or better on whitetails, 92%
or better on mule deer, and 95 % or better on elk.

• Not necessary to accurately determine age of deer less than 2
½ years old at time of death. Deer, like humans, have baby
(fawn) teeth that are replaced by permanent teeth in the first 2
years of life in a very predictable way.

• Aging by use of cementum annuli requires two teeth sent to a
lab for a forensic histological process that ultimately allows the
cementum rings to be counted under a high powered
microscope.

• The two preferred teeth to be removed and tested in most
game animals are the two center incisors from the front lower
jaw.

• With practice, it only takes 3 or 4 minutes to remove these teeth
from a freshly killed animal.

• In whitetails these two center incisors are permanent at about 6
months of age, the same as elk and moose.

• In mule deer these two center incisors are permanent at about
1 ½ years of age, the same as pronghorns, goats, & sheep.

Henry also included a picture of the cross-section of a molar so that you can see the annual “rings”, if you will.

Deer Molar showing growth rings
This photo shows 9 years of age.

Tom Remington

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