From a physiological/behavioral perspective (the two are inseparable, of course), white-tailed deer are unbelievably hardy and clever. If not for their seasonal metabolic adjustments, shelter-seeking tendencies (often requiring long-distance migration), and energy conservative nature in response to harsh winter weather, there would be no whitetails on northern fringes of their geographic range.
I’ve written this before for the pages of Deer & Deer Hunting, but it deserves repeating: There are many trade-offs — involving nutrition, shelter, and predator risk — in the whitetail’s tactical bid for winter survival. However, it’s as though the stressed whitetail possesses its own sophisticated computer system necessary to calculate energy cost-benefit ratios, predict potential predator risks, and make the best judgments possible in order to survive. Here, we have an animal that is an expert in opportunism.
The key to winter survival of whitetails on Northern range hinges upon favorable winter habitat — areas commonly referred to as “deeryards” — where good shelter and quality browse occur in close proximity.
The Migratory Problem
Unfortunately, because their summer and winter ranges are often widely separated, many deer must migrate twice annually, traveling considerable distances from one seasonal range to the other.
Keep in mind, throughout the upper Great Lakes region, only 10% to 15% of the habitat will naturally support deer during winter. Herein lies the problem: Although deer might be sparsely scattered on summer range, often well below biological carrying capacity of the habitat, concentrations of several hundred deer per square mile are not uncommon in many deer wintering complexes.
During the autumn hunting season, many deer are still on their summer ranges, often miles from their traditional wintering grounds. So in order to reduce deer browsing pressure within a given deeryard, antlerless deer harvests must be focused on a relatively large geographic area encompassing both summer and winter ranges used by the herd.
Likewise, many deer wintering complexes are under private ownership. This means any forestry/land-use management practice that does not consider the long-term welfare of wintering whitetails, even on small areas of critical winter deer habitat, can negatively impact the deer herd over a large area.
Hence, it’s important for wildlife managers to know the migratory patterns of deer using any given deeryard, to know the distance and direction deer travel, and be able to delineate the total geographic area that any given deeryard serves.
The Study
About 30 years ago, the late wildlife supervisor, Dick Aartila, called me with a rather unique problem. It seems a group of Michigan sportsmen wanted to become more directly involved in deer management. “Did I have any ideas,” he quizzed.
I suggested he have the sportsmen trap and tag deer. Hopefully, return sightings and recoveries of marked deer would help to more accurately determine the migratory behavior of deer associated with critical white cedar and hemlock wintering areas.
Sportsmen across the state took to this project with unbelievable enthusiasm and zeal. They built portable deer traps, hauled them from one trapping location to another, and ultimately trapped, wrestled down, and tagged more than 2,600 deer.
Deer trapping was carried out primarily at known deer winter concentration sites, especially where timber harvesting operations were in progress, January through March, 1989 to 2006. Generally, six to 12 traps were deployed at each site and pre-baited with corn for about a week prior to trapping in order to pre-condition deer to the traps.
All deer were handled manually — that is, without the use of drugs. This involved grabbing the deer by the hind legs and literally wrestling it to the ground. Within a few minutes the sex and age (adult or fawn) were recorded, a numbered plastic livestock ear tag (color coded to a given deeryard) was attached and the animal was released — a procedure often resulting in a few bumps and bruises for the handlers but minimal wear and tear on the animal.
The public then notified the DNR of subsequent marked deer observations, which included live sightings, hunter-harvested animals and deer killed on highways. Biologists mapped these locations to determine migration distances and annual range for deer that occupied each deeryard.
During an 18-year period, 2,694 deer were captured, tagged and released in 28 deeryards. An average of 96 deer were tagged per winter concentration site, but trapping success varied from a low of six deer to a high of 249.
Observation Rates
Thirty-eight percent (1,030 deer) of the tagged deer were subsequently observed at least once. Most (64%) were seen only once, generally during the year they were tagged. But one was observed 13 times and another 19 times.
In other words, 62% of the tagged deer literally disappeared.
Although a few were reported 12 years following tagging, only about 10% of the observations were recorded two or more years after being tagged. Nearly half (48%) of all deer observations were made during October and November when deer hunters are active.
Observation rates of tagged deer also varied among tagging sites. For example, only 26 of 174 deer (15%) tagged in one deeryard were ever observed afterward. In contrast, 28 of 39 deer (72%) tagged in another yard were observed at least once. Apparently, observation rates of deer hinged heavily upon the proximity of the tagging site to human population centers.
Sex-Age Differences
Forty-nine percent of the bucks tagged as adults were observed, at least once, compared to 36% of the adult does, 38% of the buck fawns and 37% of the doe fawns.
This adult sex difference is not unexpected, of course, since hunters are more apt to kill and report antlered bucks, rather than antlerless deer, which comprise a smaller percent of the annual harvest.
Because a high proportion of the tagged deer were never observed, it seems reasonable to assume that most of them succumbed to natural causes, especially during harsh winters typical of this northern region.
This data might also suggest that male fawns were more likely to die due to malnutrition during winter, since buck and doe fawns were observed at about the same rate the next autumn. That is, since hunters are more likely to shoot yearling bucks rather than yearling does, fawn sex differences in observation rate should have been similar to that noted for adults in subsequent years.
Given the light antlerless deer harvest throughout much of the region, it’s more difficult to explain the low observation rates for adult does. Because deer are normally reluctant to enter traps, females in the poorest physical condition (the hungriest) were probably the first ones captured — many of which did not survive the winter.
READ: 5 LESSONS ON WHITETAILS TO REMEMBER
In this region, adult deer typically make up about 70% of the wintering herd, while fawns comprise about 30%. However, in this study, 54% of the deer captured were fawns, 37% adult does, and 9% adult bucks.
Obviously, fawns are more easily trapped than adult deer, hence contributing to an inflated fawn per doe ratio of 1.5 fawns per doe among tagged animals. To the contrary, this region’s deer hunters on average report seeing only about 0.5 fawns per doe during the November firearms season — suggesting that about 50% of the fawns die soon after birth.
Assuming adult bucks and adult does were equally trapable, (which might not be the case) the post-hunt doe-to-buck ratio was 4.2 to 1. This compares to about three does per buck reported by hunters during the first day of the annual firearms season. In other words, adult deer sex ratios are not nearly as skewed to females as most hunters believe.
Migration Distance
Many deer that reside on summer ranges in areas of high snowfall migrate southward to areas of lesser snowfall during winter. These deer tend to travel long distances and can be classified as “obligate” migrators because they tend to migrate every year, some spending as much as five months annually on winter range.
In contrast, many deer in the southern areas are “conditional” migrators. They move shorter distances from summer to winter range, only during the most severe weather, and spend less time in winter cover.
The greatest distance between tagging site and observation for deer in this study was 53 miles. Fifteen deer were sighted 40 or more miles from their tagging site, and all 15 were observed in the same county.
The average distance from tagging sites to summer observations was 11.6 miles for does and 10.6 miles for bucks. These distances are somewhat greater than the average (8.6 miles) previously reported for U.P. deer and for deer in northern Lower Michigan (9.4 miles).
The fact that does were observed at greater distances from tagging sites is somewhat surprising, given that bucks tend to disperse 2 to 20 miles from their mother’s home range. If buck dispersal movements were random, we would expect some tagged bucks to move farther away to establish new home ranges. So it appears that dispersing males are more likely to move toward familiar winter concentration sites, as Mike Nelson and Dave Mech reported for deer in northern Minnesota.
We expect deer to return to their traditional yarding areas, winter after winter. But this might not be the case, as revealed by the relatively large average distance between consecutive winter observations of individual deer — 4.9 miles for does, 4.2 miles for bucks.
These long distances between consecutive winter observations of the same deer could be due to mild early winter weather and delayed or incomplete migration movements.
On the other hand, wintering whitetails might be much more mobile than previously thought, and eagerly seek (or are literally trained to seek) active timber cutting operations for food — a finding that could be critically important when managing winter deer habitat.
If wintering whitetails are highly dependent upon winter logging operations for sustenance (i.e., survival), as some biologists suggest, then natural selection would logically result in perpetuation of such behavior.
Annual Range
This study demonstrated that distinct populations of deer are associated with individual wintering complexes. However, the total annual range occupied by deer populations using any given winter complex were highly variable, in some cases due to small tagged deer sample sizes. But the majority of wintering complexes had annual deer population home ranges ranging from about 300 square miles to 500 square miles in size. One wintering complex had by far the largest annual range, covering about 2,388 square miles — amazing!
The large size and importance of that wintering complex has been known for a long time. However, this new data indicates the annual range for this particular deer population covers far more geographic area — and therefore is much more important to the region — than biologists originally estimated.
Based upon limited data, biologists estimated the annual home range for the large deer wintering population in 1987 covered about 1,400 square miles — obviously a gross underestimate.
At that time, this deer wintering area supported about 43,000 deer through winter. However, corporate forest-management practices emphasizing production of wood products, as advocated by the primary landowner, have since then fragmented and degraded the hemlock and white cedar stands in this area. As a result, the wintering complex has lost much of its former deer wintering value and now likely harbors fewer than 25,000 whitetails — a good example of how unfavorable forestry practices on a relatively small area of critical deer winter habitat can impact deer numbers over a vast area.
Conclusions
This hands-on deer tagging project required more cooperation, and did more for improving relations, between my home state’s sportsmen and biologists than any other such venture I know of. Even today, those involved still talk fondly of their “deer wrestling” days.
To effectively manage deer wintering habitat, it is essential to control deer numbers via controlled antlerless harvests. Likewise, in order to harvest surplus deer, managers must know where those deer are during the annual gun-deer season.
Data like this provides such critical information, makes it possible to establish meaningful deer management unit boundaries and more accurately set antlerless deer harvest quotas to control deer numbers using a specific wintering complex.
Also, if deer contract diseases, such as bovine tuberculosis or chronic wasting disease, biologists now have basic data to calculate how these diseases might spread, and more effectively formulate containment and eradication programs.
Unfortunately, the majority of deer tagged in this study simply disappeared — likely due to rigors of the tough winter climate and resultant malnutrition related mortality. Clearly, winter weather and the quality of the winter habitat still determine relative deer abundance.
— John Ozoga is a retired deer research biologist from Michigan. This year marks his 26th anniversary as Deer & Deer Hunting’s research editor.
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