Understanding The Whitetail "Limiting Factor"
November 16, 2010
Find the habitat element that's in shortest supply and highest demand and you'll likely find the deer.
I didn't know why or how, but I sensed I was not alone. Sitting high in a white pine overlooking a long-neglected apple tree I hadn't seen anything, though my eyes scanned the brush for any telltale shape, color or flicker of movement. I hadn't heard anything either. The woods were quiet, too quiet in fact. Yet somehow, I still felt the presence of another creature.
That's when it hit me. For the past two hours, I'd been mesmerized by the high-pitched chirps of crickets, so steady and hypnotic I didn't even notice them, until they stopped. Something had to be stirring out there to make them all suddenly cease. That's when I heard the faintest rustle of leaves and caught a glimpse of movement, just as the big doe stepped out of the dense cover scarcely 15 yards away.
As deer hunters, we're forever searching for things. Before the season, we search for sign, like tracks, trails, scrapes and rubs. During the season and while on stand, we look and listen for sights and sounds that will alert us to the presence of a deer. Though they're much harder to recognize, sometimes it's the missing pieces that are of greatest importance.
Biologists use the term "limiting factor" to describe anything that tends to make it more difficult for a species to live and grow, or reproduce in its environment, due either to its presence, or absence. For example, the major limiting factor for northern deer is lack of adequate winter cover. In arid regions, it might be lack of water. Whatever the case, find the habitat element that is in shortest supply and highest demand -- the limiting factor -- and you'll likely find the deer.
Down on the Farm
Take agricultural areas, for example. Hunters often key in on food sources. But food is obviously not a limiting factor here, at least early in the season. It doesn't make much sense to key on food sources when you're surrounded by hundreds of acres of corn. When the element in shortest supply is dense bedding cover, you may be more successful targeting that. Find the cover and find the deer.
The situation changes dramatically, however, when the crops have all been taken in. Suddenly, food becomes the limiting factor. How you modify your approach from early to late in the season may be very subtle, perhaps hunting the same travel corridor, but hunting closer to bedding cover in the early season and closer to food sources later on.
The Essence of All Life
In drier regions such as Texas and parts of the West, it's pretty obvious water is often a limiting factor. Where it's in very short supply -- isolated water holes, for example -- you can hunt the water, a favorite tactic of pronghorn and elk hunters. At the opposite end of the spectrum, say in the bottomland swamps of Alabama, keying in on water is probably not your best plan of attack.
But water availability, and therefore it's importance, occurs on a gradient. It may not be scarce in the rolling woodlands of Wisconsin or broken farms and woodlots of western New York. But I'd sure want to be sitting over a small ephemeral pond on an exceptionally warm afternoon during a particularly dry fall. Even where water exists in modest amounts, it can be a limiting factor. Water is important because wetter areas will have the most nutritious vegetation. Hunt there.
The Cost/Benefit Analysis
Often it is energy that is the limiting factor for whitetails. This can mean energy obtained from food, or the amount of energy needed to obtain food. Like a good economist, deer will try to minimize the cost/benefit ratio, seeking the most energy-efficient means of obtaining the most nutritious food.
Research has shown that, where available, acorns are by far the whitetail's most preferred food source in the fall. They are an easily obtainable source of carbohydrates deer need to fatten up before winter. In agricultural areas or mixed habitats, they're something of a luxury, but in areas dominated by hardwood forest, they can actually be a limiting factor to deer and squirrel populations. The scarcer they are, the more important they become, to deer and to hunters.
In the Northeast, for example, the deer kill is often directly related to acorn abundance. In years with lots of acorns, deer don't need to travel far to feed, and the harvest tends to be a bit lower than average. When acorns are scarce, deer travel more, making themselves more vulnerable. Even in bad years, however, there are usually a few acorn-producing oaks. Rest assured deer will find them. If you do too, you may be in for some exceptionally good hunting.
Maximizing the cost/benefit ratio can also mean thermoregulation, particularly in northern regions. In northern forests, deer migrate to traditional wintering areas dominated by a dense, softwood canopy. This intercepts snowfall, reducing snow depth and facilitating easier travel. The softwoods also buffer deer from winds. In late fall, or when winter arrives early, these areas can be as important to the big woods hunter as late-season food plots are to the Midwesterner. In northern or western plains habitat that lacks extensive forest but experiences equally cold temperatures, south-facing slopes play a similar role.
Different regions and habitats call for different tactics. But every one has something that is in particularly short supply, something deer need but must work hard to find. You should do likewise in your pre-season preparation. Look harder for the important habitat elements that are in shortest supply and greatest demand, and you may find it a sound investment, which is a rare commodity in this day and age.