Herd Stress Management
September 22, 2010
What do all of the following have in common?
In the Peace River region of northern Alberta, bucks seldom live to more than 4 years of age, despite low hunting pressure.
In the Southeastern U.S., whitetails are often covered with ticks and deer mites.
In South Texas, only about 30 percent of the adult does still have surviving fawns when fall arrives.
In the Central Texas Hill Country, you can ride rural highways almost anytime of day and see deer feeding.
In the river bottoms of eastern Montana, Wyoming and the western Dakotas, hemorrhagic disease sweeps through the whitetail herd about every six to eight years and kills off much of the population.
And finally, bucks in many places aren't nearly as big as they were 25 years ago.
Again I ask the question: What do all of these situations have in common? The answer is simple: stress!
Over several decades of hunting and managing deer, I've come to realize just how insidious stress is in a herd. It can affect size, behavior, health and even survival. Stress can and does result in smaller, less healthy deer that are more vulnerable to predation, sickness, parasites, disease and death.
What is stress? For our purposes, we'll define it as a condition wherein the animal's potential to grow, function and survive is impaired.
And what can cause stress in whitetails? Several things. One, of course, is a prolonged period of extreme cold or heat. Under such conditions, the introduction of other complicating factors, such as feral dogs, predators or even something as benign as cattle, can quickly take a toll on deer. (If you doubt cattle can be a factor, consider that when temperatures top 100 degrees in South Texas, fawns can die simply after being jumped by cows and forced to relocate.)
The effects of extreme cold and deep snow are well known and can even detrimentally alter a herd's social and behavioral patterns. For instance, in 1998 in western Montana, record snow fell suddenly before the rut and virtually trapped deer in isolated pockets. This disrupted movement to the winter range, the rut and normal social behavior. All of this initiated stress that, along with an eventual lack of food, ultimately led to a 60-80 percent herd die-off.
The rut is another source of stress, especially in bucks. The high level of activity, reduced feeding and the general physical abuse bucks endure place great stress on them. In fact, more otherwise healthy bucks succumb to "post-rut mortality" than to any other form of natural death.
As noted, livestock can stress deer. But the harassment and/or displacement by people, dogs, development and/or heavy equipment can as well. I saw this back in my early years on Middle Georgia's Burnt Pine Plantation, where feral dogs were a big problem. They constantly chased deer and kept them on edge and under stress, resulting in low reproductive success and lower body weights -- and perhaps other problems not readily apparent.
Obviously, disease and parasites bring plenty of stress, but as often as not, these ailments are the result of stress, not the original cause of stress. So what is at the root of this problem?
Malnutrition is the principal source of stress in herds across North America, and it lies at the root of many of the problems herds face today: diseases, parasites, low tolerance for extreme weather, low reproductive rates, low body weight, poor rack development and, believe it or not, even road kills. Healthy, well-fed deer can usually ward off the effects of other contributors to stress, but a malnourished deer is under constant stress and can be thrown into a tailspin by almost any added adversity that comes his way.
Let's look at some specific examples of stress-related problems. I mentioned that even road-related mortality can be related to stress. How can that be? It's simple. Hungry, stressed deer have to move and feed often and are willing to expose themselves to dangers they otherwise would avoid, including highways. The simple fact that they move more increases their chances of being hit by vehicles. Couple increased movement with the attraction that green, often clover-laden roadside rights of way offer hungry deer, and you have a recipe for a lot of insurance claims.
Until the big winter kill of 1998, the Swan Valley of western Montana, which is heavily wooded with little agriculture, was terribly overcrowded with deer. It wasn't unusual to see upwards of 100 hungry deer feeding along a 20-mile stretch of highway. It was no wonder the Swan Valley had more deer collision insurance claims than anywhere else in the state. One fellow hit five -- yes, five -- and he did it all in one night, in 50 miles! The deer were on the road because they were starving, and the right of way offered the best food available. Sadly, this isn't an unusual situation.
Stress simply forces deer to be more visible. If you ride through the Hill Country of Texas, where deer are notoriously overcrowded, you'll see them moving around during all hours of the day. You'll even see them lying in suburban yards like so many cows. Why? Because hunger-induced stress has removed their natural caution and forced them to abandon their natural low-light movement patterns. They must scrounge around all day, often in places no self-respecting whitetail should be.
The fact is that severely stressed deer essentially become tame, their hunger overcoming their natural instincts and fear. That's one of the reasons I say fair chase suffers in cases of severe overcrowding. Conversely, well-fed deer on good natural habitat are largely nocturnal, quick to respond to hunting pressure, wild as banshees and hard to hunt. It's a matter of stress, or the lack thereof.
Stress has strange ways of taking a toll. When I first bought my ranch in South Texas, stress killed deer, or allowed them to be killed, in ways I never imagined. One of my first jobs on the ranch was to get a handle on the status of the herd, including natural mortality. I assigned my ranch manager the job of cruising the place every day, checking for dead deer by watching for telltale activities of buzzards, caracaras (another scavenging bird), and/or coyotes.
In that first year, two surprising forms of mortality showed up. One, during the hottest summer days, when the temperature topped 100 degrees, we frequently found dead fawns, many of which showed no visible reason for death. The other surprise was the mortality of pregnant does heavy with fawns. In one six-week period in June and July, we found 16 does killed by coyotes, nearly all of which were about to give birth. (The rut is far later there than in much of the rest of North America.)
What could this have to do with stress? First, the herd was badly overcrowded and stressed when I bought the ranch. In that stressed condition, the does had a hard time supplying enough quality milk to fawns. As a result, the fawns were badly stressed. When the temperature hit three digits, the fawns, their tiny bodies unable to adequately insulate their vitals, were vulnerable to heat prostration. This vulnerability was exasperated when anything, real or imagined, spooked the fawns.
Does being chased by coyotes certainly might have also suffered from heat, but more likely the nutritionally stressed does simply didn't have the stamina necessary to escape pursuing coyotes when hampered by advanced pregnancy.
Evidence that stress was a major contributing factor to both of these forms of natural mortality came when the nutritional plane was raised through food plots. Once plenty of high-quality food was available, both types of deaths were virtually eliminated.
Another form of stress-related mortality was also very evident on my ranch, but it wasn't unexpected and certainly isn't unique to my ranch. I'm talking about post-rut mortality. This is a fancy way of saying buck deaths related to rut stress. It's real and it can be high, accounting for the death of as many as 30 percent of active breeders.
True, not all post-rut (or rut) mortality is directly related to stress. Often, death comes from fatal injury, usually from fighting but also from rut-induced carelessness and foolishness, or from becoming locked with another buck. Even the healthiest bucks are vulnerable to such fates, but stress can greatly increase post-rut mortality.
When I was managing Burnt Pine Plantation, there was a time during the early years when 4 1/2- and 5 1/2-year-old bucks seldom showed up, despite the fact that we limited the mature buck harvest to a number that should have ensured the presence of a reasonable number of such deer.
I finally figured out what was happening. At the time, we were overcrowded; the state had greatly reduced the number of days during which does could be shot. This also led to a relatively poor buck:doe ratio. Because we were just getting into our management program, we had a fairly young buck age structure, with only about 15-20 percent of the bucks being 3 1/2 years old or older.
This meant that relatively few mature bucks were serving as the dominant breeders in a herd with a disproportionate number of does, resulting in great stress on the mature bucks. As a result, the active breeders came through the rut beat up, worn out and as much as 30 percent lighter than they were when the rut began. Exhausted, hungry and with dangerously low body reserves, many fell victim to post-rut mortality, especially when their plight was exasperated by prolonged periods of cold and/or wet weather, harassment from feral dogs or coyotes, or any number of other challenges.
I have seen the same lack of older bucks in northern Canada, even through the region has very little hunting pressure and a lot of good food -- at least, during the warm season. What kills the bucks? Stress-related post-rut mortality.
Even though the bucks go into the rut in great condition, the rigors of rutting activity stress them enough to make them vulnerable to the extreme cold and deep snow that inevitably come to that harsh land. There, just a little stress can make the difference between life and death. That's why you don't see high populations in the northern fringes of the whitetail's range: The population must stay low enough so that every deer has enough of the highest quality food to maximize its body condition and thus its chances of surviving brutal winter conditions.
Stress is an open door to disease and parasites. Once such scourges take hold, stress increases even more; the slide down the slippery slope to poor quality/health and ultimately death is accelerated.
An earmark of stressed herds is external parasites, particularly ticks and deer mites. If you see whitetails with heavy tick loads, you can be sure those deer are nutritionally stressed. The immune system of healthy, well-fed deer is capable of rejecting major infestations of ticks and most other external parasites, but that's not so with poorly fed, stressed deer.
When I bought my ranch in South Texas, deer there were loaded with ticks and deer mites. But since we implemented our food-plot program five years ago, we've eliminated ticks and deer mites from our deer. The last time I saw a buck with ticks was three years ago, when my son-in-law shot an ancient, nearly toothless buck that was clearly stressed and starving. I've also seen parasites disappear with the arrival of high nutrition in many other places.
Interestingly, I've seen heavy parasite loads on deer in parts of the Midwest, where agriculture is generally thought to provide awesome nutrition. It does just that -- where the right agricultural practices exist. But it's a catch-as-catch-can deal, wherein good deer food exists sporadically from place to place and year to year. In any given year, the Midwest offers great nutrition -- in certain places, and in a sense, by accident. If you're a deer manager, you don't want to depend on happenstance. Food plots take the guesswork out and put consistency in.
Nowhere is the disease potential of a stressed herd more evident than on the river bottoms of Montana, Wyoming or the Dakotas. Here, ribbons of trees and brush trace the river courses and provide limited cover in the middle of wide-open plains and prairies. Irrigated alfalfa fields along the bottoms and wheat fields on the adjacent uplands provide a super abundance of high-quality food.
For all practical purposes, here you have a contained herd (the open prairies essentially are a "high fence") supported by a nearly year-round food-plot program. Alfalfa offers high protein during the warm season; wheat provides energy during much of the cool season. It's a perfect "food plot" program . . . to a point.
Because cover and space are more limited than quality food, deer numbers grow until they finally saturate the limited cover. The concentration of deer in some of these river bottoms surpasses virtually all other known density levels. In fact, I once saw more than 200 deer file out of a 75-acre block of woods on the Milk River in Montana! That's a density of nearly three deer per acre of cover: an unheard-of number!
While an extremely high deer density can bring on stress in itself, the high nutritional quality appears to override the usual social stress of so many deer concentrated into a small area. But alas, there's a limit to everything, and at a point, the number of mouths exceeds the capacity of even this super "food plot" scheme to keep filled. Stress enters the tightly packed herd, which is living nearly nose-to-nose, and the door is thrown open to disease. The "predator" that almost always steps through that door is hemorrhagic disease, or blue tongue. In a matter of weeks, usually in the fall about six to eight years after the last outbreak, it kills from 50 to 80 percent of the stressed herd!
Yes, stress is an insidious thing, leading to smaller antlers and bodies, lower reproduction and aberrant behavior, even death. But we aren't without the means to cope with it. I'm talking about sound management, which means keeping the herd in line with the food supply.
To correct the problem, we have two choices: Lower deer densities to match the available food or increase the food supply to accommodate the number of deer we want. I like the latter option far better. And with that, I think I'll engage in a little stress relief for both the deer and myself . . . by planting some food plots!