Burroughs Backyard

Backyard biology from a field ecologist's perspective

Deer Checking

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Warning: though the content here is cool, some may consider the pictures below to be rather gruesome. In fact, they are pretty gross. But biology can often be pretty gross, right? Especially when you’re talking about dead things. 

Now, on with the show.


What am I doing in this picture?
looking a dead deer in the mouth
 If you guessed “looking in the mouth of a dead deer”, you’re right.

More specifically, I’m examining its teeth to determine how old it is (was).
This buck? Three and a half.

Deer aging can be a bit gory, and before doing this last year I’d never handled so many dead vertebrates before. I’d never even considered the procedure of butchering anything, since I grew up in a family of non-hunters and became a vegetarian early in college. But here are some reasons I examine the mouths of dead deer with gusto:

1) The aging itself is interesting and sometimes challenging
All the deer we age come in half-years, since they’re born in the spring and we’re looking at their teeth in the fall. Based on the replacement of teeth (they lose their baby teeth and replace them with adult teeth during the first year-and-a-half of their life) and the wear of their adult teeth, we can make a pretty good guess towards their age. As a deer gets older, the hard outer enamel of its molars wears away to expose the softer, brown dentine in the middle. Observing how much dentine is visible in which teeth, you can determine, relatively well, how old they are.  Sort of like looking a gift horse in the mouth.  Only with deer.

The first time I was looking at our practice teeth (a collection of bleached jawbones with agreed-upon ages), I was a bit baffled by the tooth structure. The molar of a deer is much more complicated, in terms of surface area, than the molar of a human. There are multiple portions, which I at first had trouble distinguishing from separate teeth. And on each portion of the tooth, there is a lingual cusp (on the tongue side) and a buccal cusp (on the cheek side). Each of these 4 cusps on a tooth might wear in different ways, exposing dentine at different ages.  Unless you can tell which tooth a cusp belongs to, it’s not going to tell you a whole lot about the age of the deer.  (Aside: have you ever seen an elephant’s molar?  Talk about different structure! It makes deer molars look WAY simple!)

In our region, most deer that get brought in are between 1.5 and 3.5 years old. Because of hunting pressure, the bucks (males) rarely make it past that age. It’s more common for the does (females) to live a bit longer, and I’ve seen a few 6.5-year olds while aging this year. At that point, their teeth are worn down close to the gum line, and it’s hard for me to imagine them getting a whole lot older without starving.

Why is deer aging challenging? For one thing, the teeth can wear differently based on diet. Telling 2.5 from 3.5 can be tough if the enamel wear is in-between the idealized amounts you would expect for those ages. For another, the molars and premolars are in the very back of the deer’s mouth. For many deer, we can cut their cheek to make the teeth easier to see. On trophy bucks that hunters want mounted, however, it’s more of a challenge to peer down their mouth with a flashlight and hope there’s not blood covering the teeth we need to see.  Gory?  Sometimes.  Interesting?  Yes.

Here are a few images of teeth, to show some of the differences.

yearling 1 DSCN1583 DSCN1576
This deer was 1 year, 6 months old. Its second premolar is a baby tooth with 3 cusps. In this picture, it’s getting pushed out by the adult premolar emerging underneath. This deer was 1 year, 7 months old. All 3 premolars are adult premolars, but you can see that the 2nd and 3rd premolars are very fresh and new. The last molar in the back of the jaw, the 3rd molar, hasn’t come all the way in yet. This deer, an adult, was 3.5 years old. All the teeth are adult teeth, and the wear on the 1st molar has a diagnostic amount of dentine showing between the white enamel.

2) It’s part of my job
The DEC tries to age a large proportion of the deer taken by hunters to understand the population structure in different parts of the state. In addition, comparing the age of a buck to his antler beam diameter (how thick it is at the base) can give you information on the health of the herd. In general, the message from all the deer in the mid-Hudson Valley is that the population is HUGE, the population structure is biased towards young deer, and they’re  eating VERY WELL.  As well as looking at teeth, we collect the heads from some of the deer so they can get tested for Chronic Wasting Disease (CWD), an emerging disease of cervids (deer and other similar hoofed animals). Aside from being fatal for deer, at this point nobody knows the long-term health implications for humans, or even whether it’s transmissible to humans. There is no CWD in New York, though in the past few years it has shown up in more states, including NJ.

3) I enjoy eating venison
Wait, didn’t you mention that you’re vegetarian a few paragraphs back???
Yes, for the most part. I’m vegetarian for ecological reasons: it takes a lot more resources to make animal calories than plant calories. The ratio is approximately 10:1, so that it takes approximately ten times more land, water, petroleum, fertilizers, herbicides, pesticides, fungicides, emissions, shipping, packaging, etc., etc., etc. (did I mention water and petroleum?) for a human to eat animal calories instead of vegetable calories.  Luckily, it doesn’t take a whole lot of fertilizer or pesticides or petroleum to grow a deer (at least not a wild deer…incidentally, it’s illegal to sell wild venison in New York, so any venison you see on a restaurant menu here is farm-raised which seems…. silly… to me.)

The punchline is that, in New York and many other parts of their range, the deer population is large enough that they’re actually damaging the ecosystem – they’re overeating. Or rather, enough of them are eating that in many areas, forest regeneration has more or less come to a standstill. They eat the tree seedlings and saplings before they grow into mature trees, and many forest understories look park-like because the next generation of trees doesn’t exist.  They’ve all been eaten and converted into deer.  There are some cool scientific studies on this, which I think are better saved for a later post.  Anyway, deer are retarding forest regeneration, and also don’t take extra inputs of resources to produce. Because of all this, I don’t have a problem eating deer.

4) I enjoy learning new things
Not much more to say about that, except that looking at dead deer teeth was definitely new for me last year.

Final thoughts:
There’s a song we sing at the farm, written by our farm manager, that’s about making sure you don’t get Lyme disease from ticks. Part of the refrain is “quick, quick! Pick off the tick!” We sing a lot at the farm, and it’s easy for song lyrics to come to mind when they remind me of something.  When my coworker and I were checking a fresh deer and I looked down at my sleeve to see a deer tick crawling over it, I instinctively said “quick, quick! Pick off the tick!” My gloves were a little bunchy around the fingers, so I pulled my hand temporarily away until I could remedy that and grab the nasty little arthropod. But my coworker looked at the tick, looked at me, grabbed the tick and flung if off. It wasn’t until 20 minutes later, as we were walking back to the car, that it occurred to me to explain: “I’m sorry! Before when I said ‘quick, quick! Pick off the tick!’ I wasn’t trying to give directions; it was just the line to a song!” She started laughing: she hadn’t thought I was that scared of ticks.

Deer tick, deer tick, get off of me
I don’t want no Lyme disease!
Take away your spirochetes
Deer tick, deer tick, get off of me!
(song by Creek Iverson)

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