Do Your Deer Have Adequate Browse?
May 02, 2016
There are many reasons for the whitetail's amazing success as a species. One of them is its ability to adapt to a wide range of food items as needed.
Plants and the herbivores that feed on them have evolved to "outwit" each other as best possible. The plants have done so by developing thorns, toxins, pubescent foliage and/or indigestible leaves that make them less attractive.
Many of the herbivores, in turn, have developed their own ways of getting around these adaptations. Some have become specialized feeders, eating only a very few specific types of plants. Others are generalists and far less discriminating in their diet. Where do whitetails lie on this spectrum? Somewhere in the middle.
WHAT WHITETAILS EAT
Go to any game management textbook and you'll find largely the same verbiage: Whitetails eat a variety of plants and plant parts, including trees, shrubs, weeds, grasses and grass-likes, mushrooms, fruits and nuts.
All of that is true. But whitetails sometimes eat other items, too. They browse kelp on the beaches of New Zealand's Stewart Island and Quebec's Anticosti Island. They've been witnessed eating songbird eggs and live hatchlings, along with fish washed onto lakeshores. Starving deer even have been seen eating road kills of their own kind.
Of course, these are items whitetails have been known to eat, not what they necessarily prefer. As managers, we want to give them what they want and what their bodies are best equipped to utilize.
Whitetails and other ruminants (including cattle) have in the rumen tiny organisms (bacteria, protozoans, fungi and yeasts) that help to break down plant material into protein, energy and minerals. The most important compounds produced in this fermentation chamber are volatile fatty acids, the main source of energy for everything from running to producing milk, growing antlers and supporting other body functions.
Unlike many other ruminants, such as bison, antelope and some other deer species, whitetails aren't well adapted to digesting heavily fibrous plants, such as grasses. They basically are limited to the more easily digestible plants and plant parts. So what satisfies this need?
I'm convinced that if whitetails were given their choice among all plant categories, they'd pick certain weeds as their favorite foods every time. Yet the term "weed" includes almost countless species, most of which for various reasons a deer wouldn't even consider eating. So that narrows down the field of good deer plants considerably.
The reason some weeds aren't favored for forage lies in the chemicals they produce to keep from being eaten. A good example is a southern plant called croton, or "dove weed." It gets its name from the fact it produces seeds highly favored by doves. If you harvest the plant itself and have it tested for critical nutritional components, it actually tests out pretty well. But the plant manufactures chemicals that thwart digestion. Even cattle will walk away from it.
Weeds (biologists prefer the term "forbs") have another problem in regard to supplying a reliable food source for deer; they tend to be ephemeral, meaning they come and go quickly with climatic conditions. In droughty years forbs tend to disappear, leaving much of the ground surface devoid of usable food.
What about grasses? They're full of highly indigestible fiber, making them difficult for deer to digest. Secondly, most of the body mass lies underground, removing a lot of potential food from the forage game. Whitetails don't depend on grasses except during early stages of growth, when shoots are more digestible.
That brings us to mushrooms. Don't underestimate the volume of mushrooms produced during the average year. These fungi are important sources of protein and phosphorus, the latter of which is one of the most critical nutrients for antler and milk production.
Of course, mushrooms come and go, making them less dependable than we'd prefer. Likewise, various fruits and nuts are highly preferred by deer, but they're only seasonally available. And like mushrooms, they're also highly dependent on the right weather cycle.
So what's left? The one type of plant material on which whitetails have evolved to depend: browse.
A DIETARY MAINSTAY
Browse is the collective term for the leaves and twigs of woody plants: shrubs, small trees and vines. Some of these plants are almost always present, even during extreme drought. In 2011, we experienced a "millennial" drought, along with above-average summer heat here in Texas — but amazingly, most trees and shrubs somehow held on. Their root systems reach far underground, and they go dormant to protect themselves during such stressful periods.
During my recent stint as "Deer Czar" of Wisconsin, I discovered the primary culprit in the loss of credibility of that state's Department of Natural Resources, in the eyes of the public, involved the use of computer models to predict a given year's deer population. The model turned out not to be very accurate, leaving DNR staff to annually calculate an indefensible number (population goal) that never was achieved.
I suggested the DNR let the deer and the habitat say how they're doing. That's precisely what you should do, as well. If you know a little about preferred deer foods on the land you manage, you can assess habitat and herd health by conducting a simple browse survey.
DAN LAY'S DISCOVERY
In 1967, my friend Dan Lay published a landmark article in the Journal of Wildlife Management. The article was titled, "Deer Range Appraisal in Eastern Texas."
Dan, as did I, came from a farm and ranch background and thus understood animal husbandry. In an attempt to better understand the quality of habitat for whitetails, he divided browse plants into three categories: first, second and third choice. Roughly defined, first-choice plants are those deer will walk a considerable distance to eat. Second-choice plants are those they eat as they encounter them. Third-choice plants are those they avoid unless starving.
Once Dan had identified these three browse categories, the next step was to develop a way to use preferences to determine the health of the deer herd. The goal was to determine whether or not land was under-stocked with deer, fully stocked or over-stocked.
"Browse is the collective term for the leaves and twigs of woody plants: shrubs, small trees and vines. Some of these plants are almost always present, even during extreme drought." - Dr. Deer
This type of assessment is far different from numbers predictions. What matters isn't so much the absolute number of deer as it is making sure the deer present are healthy. One piece of land might have 30 deer per square mile and be fully stocked, while another meets that definition with just 10 deer per square mile. The difference is in the nature of the habitat and its ability to produce forage.
Deer roam over a certain amount of range each year, allowing us to devise a sampling procedure that doesn't worry unnecessarily about sampling design. The system I use commonly today involves establishing permanent walking lines across the landscape, letting me sample different habitat types as I go. I mark the start of each transect line with a permanent post so I can return each year to conduct my browse survey.
Although you can do one of these surveys at any time, the best period is at the end of winter. This lets you assess the accumulated impact deer have had on the browse plants since the previous growing season began. In the South, my surveys take place in early March, while up north I conduct them in April or May.
The number of sampling points is a related to property size. You need at least 20 per line on the average tract, but 10 well-distributed points will suffice.
Reaching the station marker, I randomly pick a starting direction and pace a set distance, usually 100 feet. I stop at this point and mark a circle in which I'll examine all browse plants for signs of use. This circle usually has a radius of 15-20 feet.
As I sample browsed plants within this circle, I record the species and estimate the percentage of the current year's growth that has been browsed. A good way to do this is to randomly examine 10 stems of each plant and count how many have been browsed. If four have been browsed, we'll call that 40 percent utilization.
(How do we know any low browsing sign isn't due to rabbits? Deer have no upper front teeth, so they must pinch off stems, leaving a telltale pattern. Rabbits, though, have very sharp front teeth that cut twigs at a clean angle.)
You don't need to compare the number of plants species to species — all you need to do is determine the average use of each species in that area. Then pace to the next point and repeat the process. Once you've concluded your browse survey, you can begin to analyze the data.
I concur with Dan's recommendation that you only assess browse species that are found in at least 20 percent of your survey plots, to avoid including rare plants that could bias results. Then determine which plants surveyed fall into each of the preference categories. This will require a bit of research. Every geographical region has specific plants deer prefer or avoid. The Internet is full of references to these, and your local deer biologist will gladly share his/her knowledge. You might have to learn to recognize some plants, but that's part of being a good woodsman.
In Dan's study, all three preference classes of browse were assessed. But I'll share a tip you might find useful: Only look at the average utilization of browse plants classified as second-choice species. Again, these are the plants deer tend to browse as they encounter them. They're the real mainstay for deer food.
In my experience, 30-50 percent utilization of second-choice plants means your range is fully stocked with deer. Use exceeding 50 percent throws up a red flag. Research indicates most plants can't recover adequately when more than half of their annual growth is removed. So if you reach that point, you need to make some adjustments.
USING BROWSE DATA
There are two uses for this information. First, if you conduct a browse survey on the same property each year (and especially if you use the same sampling locations), you'll be able to monitor how your deer and habitat are doing over time.
If my browse use estimates rise above 50 percent, I know we haven't taken enough does and an over-population situation is looming. If, on the other hand, browsing drops significantly, either we've removed too many deer (part of which could be through natural mortality, such as disease) or the land's capacity to produce forage has increased.
We really don't manage deer herds as much as we "fine tune" them. We conduct an action, monitor the herd and habitat for response to that action and then make adjustments to our management plan accordingly. Studying browse use is one way in which to monitor habitat quality and use.
Even while hunting I try to note how much of what the deer are eating. As we travel for North American Whitetail Television, we often find ourselves in new areas. With limited time in which to find and harvest nice bucks, it helps to be able to quickly figure out deer abundance, age and sex structure and travel patterns. If you observe browsing patterns as you scout, the deer will "tell" you where they spend the most time.
I've never seen a property that was uniformly used by whitetails; there always are "dead spaces" where deer seldom go, mainly because of a lack of food. Examine browsing along trails to see how heavily they're used.
I hope this look at browse has given you a new appreciation for how being able to read habitat and feeding patterns aids in management and hunting. It's an important skill, one that will pay dividends over the long haul.