Sunday, May 29, 2016

Understanding The Life Span Of Whitetail Deer

male whitetail deerJust about everyone who saw the Walt Disney classic “Bambi” shed a tear, or at least stifled the urge to lacrimate (that’s cry in Scrabble-ese). Even if I had known of the devastating effects deer have on forest regeneration, not to mention crops, landscapes and gardens, it still would have been a trauma for my five-year old self when Bambi’s mother got killed. (Oops—spoiler alert there, sorry.) But how might the movie have ended if they had all lived happily ever after?

What is life like for those few lucky, possibly smarter, white-tailed deer which manage to avoid cars, coyotes, projectiles and parasites beyond the first few years of existence? Could an aged deer manage to gum your hostas to a nub when its teeth have worn away? I picture a wizened Grand-Buck griping that salt licks were better when he was a fawn, and that yearlings have it easy crossing the road these days now that cars have anti-lock brakes.

Seriously though, life gets harder in many ways as organisms age. Ask anyone who retired to Florida why they left northern New York and they’ll probably tell you winters were enjoyable until arthritis and various other ailments set in. What happens to wild deer as they become senior citizens—do they succumb to age-related health issues like bad joints, decayed teeth, or tumors?

I put the question to retired New York State Department of Environmental Conservation (NYSDEC) Wildlife Biologist Ken Kogut, who lives outside of Potsdam. He laughed. “To have a deer die of old age in the wild is an oxymoron,” he said. Ken went on to explain that in terms of hunting, NYSDEC data show the vast majority of harvested deer are in the 1.5 to 3.5 year-old range (because they are born in May and June, deer are always in a half-year by hunting season). “To see a seven or eight year-old buck [at a NYSDEC check station] is very, very unusual.”

To illustrate this point, consider that the Max Planck Institute for Demographic Research states the average lifespan of captive white-tails is 16 years, with the confirmed oldest captive deer living to be an ancient 23 years old. Compare that to wild white-tails, which do not have a good track record, so to speak. The average lifespan of a wild deer? According to a University of Michigan report, two years. Yeah. Ten is considered the upper age limit, and a very rare occurrence at that.

Determining the vintage of white-tails is called aging deer, not to be confused with the aging of parents, which is a function of both the number and activity level of their children. How do we find how many birthdays a deer has had? Dentistry.

White-tails have canine teeth (the irony of which, sadly, is lost on them) and incisors on the lower jaw, but none on the upper. In other words they can’t snip off a twig the way a rabbit can, but have to tear it away with an upward motion. But they do have upper and lower molars, and the wear on these is used to tell how old a deer is. Or was, as this is generally done post-mortem.

Aging deer started as kind of a home-grown citizen-science project. In years past, keenly observant hunters who could identify an individual deer from yearling stage onward took note of molar wear when it was harvested. Years of correlation of known deer age with measured teeth wear (turns out it’s one millimeter per year) made hunters like dairy farmer and NYS Big Buck Club founder Bob Estes of Caledonia, NY, experts in aging white-tails.

Aside from hunting, another thing driving down the average lifespan of wild deer is predation of fawns by coyotes and black bears. Surprisingly, in the Adirondacks, the latter may kill more fawns than coyotes do. Predation is hard to quantify, though, as coyotes and bears eat every last vestige — bone, hair and innards — of any animal they kill or find dead of other causes. Because predators do not feel safe out in the open, they don’t eat dead deer on roadsides, which are left to rot.

Deer-vehicle collisions are another huge factor, with the New York State Department of Transportation reporting an average of 65,000 per year. But starvation during hard winters, says Kogut, is probably the single factor likely to kill older deer. For various reasons including worn molars, they are likely to have less stored body fat going into winter than a younger deer.

With all this carnage, are white-tails disappearing? Hardly. Dr. Peter Smallidge, the State Forester for Cornell Extension, says New York State had an estimated 20,000 deer in the early 1900s, fewer than one deer per two square miles. Today there are a million, more than enough to destroy the ability of many forests to regrow, as young trees are devoured by deer while they are seedlings.

Lyme disease is also a result of deer overpopulation. Cornell Extension Wildlife Specialist Dr. Paul Curtis believes that if the deer population went down below six per square mile—still higher than the historic density—then deer ticks, which spread Lyme disease, would become too scarce to be a public health threat.

What might cause the deer population to decline like that? I don’t know, but it certainly won’t be old age.

Photo courtesy the U.S. Fish and Wildlife Service.


Paul Hetzler

Paul Hetzler is the Horticulture and Natural Resources Educator at Cornell Cooperative Extension of St. Lawrence County.

You can reach Paul at the Cornell Cooperative Extension office in Canton at (315) 379-9192.




11 Responses

  1. Richard MacKinnon says:

    What is the experience of hunters contracting maladies from the venison they consume? Is enough attention given these risks? It’s not just CWD, I believe.

    • Dan'L says:

      There has been some attention paid to these matters but you don’t hear much about it. Within the hunting fraternity, however, there is much awareness but the focus is more on transporting deer carcasses from or through states with CWD.

      Most hunters will not consume the venison from a deer they suspect to be sickly and can actually get another tag issued to them if they turn the deer over to DEC, who does try to monitor such things: http://www.dec.ny.gov/press/79622.html

  2. Cranberry Bill says:

    Three things Paul, and it will take three beers.

    First, I always look forward to your superb writing. Well, that was easy

    Second, somewhere in Delaware, my home state, there was a wildlife area with a fenced-in area, closed off to deer. It showed what deer did to the fields compared to the segregated area. It was Night and Day.

    Second, I thought older and bigger deer had a better chance because they could reach higher for the goodies than their offspring.

    Third, I saw tons of deer scat in the 5-ponds area last month (2 weeks), and actually saw one of them which froze for about 5 minutes. So what, I am on my third. (I guess my point is that since the 5P is pretty much vegetated, younger shorter deer might have a better chance there.)

    Fourth: Will be looking for the invasive species “white clover” near Big Shallow in the Five Ponds this time soon. (sorry, off subject).

    Bill Ott
    Lakewood, Ohio

  3. Tim-Brunswick says:

    Great straightforward article on Whitetails> I’m a hunter and come from a Family of whitetail hunters. We used to be called “Meat Hunters” because we use what we take to help feed ourselves and Family with quality meat. Today we’re “Subsistence Hunters” and we’re among a dwindling segment of our outdoors society, which help manage Deer populations that would otherwise be out of control, particularly in suburbia.

    Thanks again for a very informative article!

    Tim-Brunswick

  4. Dave says:

    Are there any significant areas where whitetail deer are not artificially “managed” via hunting? Where they exist in a natural environment and are allowed to achieve balance with resources and predators? That of course would assume that the predators have not been artificially “managed” out of the environment in question too…

    It seems like studying such an area would be the only way to understand the real, natural lifespan of whitetail deer. I’m guessing it would sit somewhere between the artificially “managed” 2.5 year average and the 16 year average in captivity.

    • John Warren John Warren says:

      Great question!

    • Dan'L says:

      I believe there have actually been studies at Huntington Forest in Newcomb but I’m not sure on this particular subject. I know there was one on male deer dispersal. While hunting does not happen there, you can’t control where the deer go, especially bucks, once they leave their birth area (which should happen naturally) and establish their own home range.

    • Boreas says:

      It would be a great project, BUT, much of the problem is that whitetails are more prolific around border areas between fields and forest. However, this doesn’t occur often naturally in their range except where people are. Where people are, the predator/prey balance is usually messed up. In more extensively forested areas whitetails aren’t all that common because of lack of browse. That is where moose tend to take over. It might be a little easier to do the study on mule deer because there are areas out west with significant predation, but the habitat is quite a bit different and may not correlate to whitetail populations.

    • Cranberry Bill says:

      Dave, I spent some time researching this, and could not find a large unmanaged whitetail deer population. There is one in Oregon & Washington, the Columbian white-tailed, named for the Columbia River, but the population is small – read about it here: https://en.wikipedia.org/wiki/Columbian_white-tailed_deer.

      The most interesting article I found was by the Quality Deer Management Association (QDMA), a 60 page pdf with interesting numbers, especially on page 38; https://www.qdma.com/uploads/pdf/WR2012.pdf

Leave a Reply

Leave a Reply

Your email address will not be published. Required fields are marked *