By Dr. James C. Kroll
The year was 1978, and I was participating in a deer management seminar in Mississippi. Several of us “young” biologists were on the panel, and it came time for questions from the floor.
“How many does should we harvest this year?” a man asked.
A fellow panelist responded instantly, “Can you buy .30-06 cartridges in 55- gallon drums?”
The hunter’s face dropped as he sat down, shaking his head. While I shuddered at the flippant answer, I generally agreed with the basic thought. At that time, some hunting clubs along the Mississippi River had frightening densities as high as a whitetail per two acres. We had to take more does.
Back then, and for years afterwards, my view was that wildlife agencies hadn’t done a very good job of controlling whitetail populations. Without lowering numbers, such dire consequences as disease outbreaks and habitat damage were looming. Gradually, though, agencies began to take action, largely through increased doe harvest.
Is the approach we widely recommended in the 1970s still applicable in today’s deer world? Not necessarily. Whitetails are what we call a “K-adapted” species; that is, the population is controlled mostly by habitat. Yet a doe is biologically capable of contributing to an annual population increase as high as 150 percent, given good habitat conditions. Whitetails also are genetically programmed to saturate their range in as little as seven years.
Long ago, natural habitats were largely controlled by such factors as wildfires and severe weather, including tornados, hurricanes, blizzards and droughts. After a major disturbance, forests would undergo the natural process of succession. Bare ground gave way to weeds, grasses, shrubs and trees, producing large amounts of foods preferred by deer. The result was a shift from low fawn survival to high recruitment rates. A low-density deer herd rapidly became a high-density herd.
But within 7-10 years, the vegetation often grew beyond what we call the “deer zone” (from the ground up to 4 1/2 feet), shading out deer forage plants. Slowly, herd growth declined, ultimately returning to lower fawn survival and overall lower densities.
By 1900, in many places we had a landscape pretty much devoid of natural ecosystems. Forests had been cleared or destroyed by wildfires, and prairies had become fields of cereal grains or cattle pastures. Market and subsistence hunting had reduced deer numbers to the often-quoted but unsubstantiated “fewer than 500,000.”
Restoration efforts were enthusiastically accepted by hunters and landowners, and within 50 years, they enjoyed remarkable success. Unfortunately, at the time professionals and conservationists hadn’t yet given much thought to managing deer, only restoring them. The result was a runaway train.
But a lot has changed in 40 years. We’re learning that what was true in 1978 might not be so workable in 2018. At the time of that Mississippi meeting, deer conformed to what we commonly called a “compensatory” response to deer removal. I gave a paper to another gathering of deer biologists, outlining a theory that there’s a “sweet spot” of deer production at a population density of one-half what the habitat will carry. I adopted the term “maximum sustained yield” after a paper presented by a population ecologist.
About a year later, Dr. Dale McCullough published The George Reserve Deer Herd, which presented Michigan data supporting this theory. He showed that if you removed a large number of does from a herd that was hanging on at carrying capacity, there would be a compensatory bump in fawn recruitment. This led to the mentality espoused by the biologist recommending buying ammo in 55-gallon drums.
But as time passed, I began to question the long-term sustainability of this management approach. Because other controlling forces were appearing.
Not so long ago, deer biologists considered the coyote basically just a nuisance. I recall a well-known biologist at an early meeting of the Southeast Deer Study Group (an annual gathering of biologists) saying coyotes weren’t a problem. As of 10 years ago, he was publicly calling for coyotes’ heads! The predator had by then spread to the Atlantic Coast and northward into New England.
Meanwhile, public sentiment increasingly favored protection of not just coyotes but also bobcats, bears, mountain lions and wolves. Today, these species are increasing at an alarming rate. Scientific studies often report a “negligible” impact of a given predator, but the combined impact of the full suite of predators can be staggering.
In the U.S., the Wilderness Act ushered in a new philosophy in forest management. This hands-off approach caused some productive deer habitats to mature into non-productive ecosystems. Furthermore, deer themselves were having a huge impact. Years of over-browsing had all but eliminated the best native plants that had led to the population boom. The emergence of industrial farming using herbicide-resistant crops also contributed to lost deer productivity.
Many deer diseases are “density-dependent,” meaning their impact is directly related to population density. High populations were ripe for the appearance and spread of many diseases, most notably the viral hemorrhagic diseases EHD and bluetongue. Bacterial diseases also were beginning to be commonly seen in wild deer. (The much-feared CWD is not density-dependent.)
At first, whitetail biologists looked at hemorrhagic diseases as “natural,” because they’d been common in Southern herds with no apparent long-term effects. (EHD also has been known since the late 1950s in New Jersey and Michigan.) But more recently, new strains have appeared, caused by a rearrangement of the genes of an exotic strain with those of a native form. Such mutated viruses already have killed thousands of deer, if not millions.
Lastly, humans have had additional direct impacts. The number of whitetails killed annually by vehicles is equal to or greater than the annual hunter take. Increases in season lengths and bag limits have also substantially increased intentional deer mortality.
Since 2000, whitetail harvests and populations have fallen by almost 20 percent. For example, in parts of northern Minnesota and Wisconsin, increased predation, deteriorating habitat and over-harvest encouraged by longer seasons and higher bag limits have caused deer numbers to fall so drastically some hunters have given up. The old ways no longer work.
Harvest decisions must be based on data acquired locally, which few wildlife agencies have done. The Deer Management Assistance Program models developed years ago by Drs. David Guynn and Harry Jacobson need to be employed across the landscape. Biologists working cooperatively with local hunters and landowners is the best way to manage. A site-specific plan must be developed and accepted by local people, or it will never work.
Doe management is a fine-tuning process. Implement a conservative strategy, measure the response of the deer and habitat, then tweak your plan in response to what you learn. Each herd is site-specific, so doe bag limits for large geographic areas should be avoided. Unfortunately, many agencies still have problems accepting that.
Even if your wildlife agency authorizes a high bag limit on does, there’s no law saying you must kill that many! Landowners and hunters know more about what’s going on locally than do biologists at state headquarters. However, we must make decisions based on what’s really going on, not on what we wish were going on. That can mean refraining from shooting a doe even though it’s late in deer season and your freezer is far from full.
Management now is more challenging than ever. Faced with declining hunter numbers, wildlife agencies and biologists must give up on old dogma. Hopefully, young biologists will take up the challenge, just as my generation did back in the 1970s.