Antler Points

People "budget" money; they manage its flow in and out. Deer budget energy. They do this naturally and by their behavior. Around the world, animal that do it well survive; those that do not, perish. This is true for species as well as individual animals. (It is true for humans as well, but we need not discuss that important concept here. Society can learn a lot from people who really understand deer.)

Many biologists now understand the deer as an energy-budgeter. In the '70's university professors Aaron Moen, Henry L. Short, and Roy Kirkpatrick advanced this concept. It has taken a long time (as most good ideas do) to come into widespread use in the field. Even if never directly used, it is an important perspective - a place to stand - when looking at the deer resource.

The income to the energy budget is sunlight. The deer manager is not really an animal manager, but a sunlight manager. The north-facing slopes do not get much sunlight, solar radiation. They are not as good for deer - either to warm them in winter or to supply energy to plants that deer eat - as are southern slopes. The manger can't influence the amount of sun coming in very much (they are very concerned about air pollution, which they can influence), but they can improve the areas selected for purchase by hunt clubs and reserved wildlife areas. They can decide where their money will have the best payoff in sunshine units. Slopes pointing northward (315 degrees to 135 degrees) can be mapped along with others. A simple count of the acres N and acres S is the beginning of understanding about the "goodness" of a tract of land for deer. It is just the beginning.

Plants capture little sunlight coming into an area. It is of such great importance that it seems that all plants are starving and, like beggars, are grasping, reaching, clawing to get over and around other plants in order to get and hold as much sun energy as possible.

Deer eat all types of vegetation. Once called "browsers", they are best known as "herbivores" because they eat all types of herbs, grass, small plants, and stems, and they are so successful because they can get energy from so many different plants. Some people think they should be called "grazers" since they resort to woody materials where grasses are not readily available. The more dense the high-quality plants in the feeding zone of deer, the better the conditions. In green grasslands and brush fields the energy in abundant plants is abundant. Under a dense forest cover, there is little leafy matter. Leaves and green stems, from the energy perspective, are solar collectors. Stems are the storage tanks and the structure to get above competitors and into the sunlight. Energy for deer in a one-acre grassy field may be 100 times greater than on the floor of an acre of forest.

Plants have to collect sunlight by leaf-surface processes, photosynthesis. It is stored as sugar. Where is it stored? There has to be structure. That structure, over-simplified, is bones (calcium and phosphorus) and protein. The key element in protein, again over-simplified, is nitrogen. Even after being simplified we're still left with the key parts of the R* Deer management picture - energy, nitrogen, calcium, and phosphorus. The last three are of interest in another development (which we'll discuss in future Antler Points). Phosphorus is significant here in this unit because it is the basis for "bound energy", the so-called double bonds of the complex organic molecules of the deer. The energy of life is stored as the bonds of the chemical molecules.

A deer can be warmed by standing in the sun, but compared with its needs for energy, this form of energy that is gets is like desert. The real energy "meal" has to come from bound energy in plants. The only energy relevant to deer is that which they can "get to" and eat. Clearings in forests, roadsides, thinned forests, and carefully planned timber harvests are the means to supply a continual supply of energy (in the plain plant wrapper) to deer.

It takes very careful management of plant communities to stabilize a deer herd. Since this has rarely been done, deer are described as boom-or-bust populations. This is not required of them, not built into their genes. They just respond over the region to the available energy. It booms and busts. It doesn't have to and The Deer Group, through its clients and members, is committed to preventing these awful, unstable conditions.

Deer managers express energy as kilocalories. A Calorie on the box of Wheaties is one kilocalorie in the world of deer-science. There are about 4 kilocalories in every gram of stuff a deer is likely to eat. This is a good number to remember. Thus, there are about 1812 kilocalories in a pound of average deer food (easily remembered as "the War of 1812").

On average, a deer must eat a dozen (12) times its weight each year (on average, its weight each month). A herd of 30 deer in an area for 365 days needs a lot of solar collectors at work - about 28 tons of food. There has to be at least 47 tons present in the area because they must never take more than 60% of what is growing. (Taking too much reduces plant vigor.)

A small doe producing milk and a growing fawn need about as much energy as do large bucks. Average figures don't serve well very long. That is why R* Deer managers break down data into three age classes , and buck/doe categories, resulting in six different types of animals, each with different energy requirements, all changing during the year and as they age. Fortunately, our computer programs handle the numbers well.

Food may be low in energy. The deer has a second problem. It costs energy to walk to it but even more to chew and digest the stuff! There may appear to be much food available. Only by careful range and forage analyses can the energy in each type of plant be evaluated and that total - in each month! - be analyzed so that he progress and potential of the herd can be appreciated and used for its lasting benefit.

Young deer convert food into flesh. Older deer need food to maintain their "equipment" and reproduce, but they convert little of it to body weight. The production of fawns increases as energy supplies increase. This is coupled with reduced mortality. The higher the energy, the lower the fawn mortality. If we start with a herd in a part of a county, say around some creek, and it only has 3 age classes, then a gross analysis can be done as in Table 1.

Once the analyses are done (and under specific conditions we use exact amounts of food eaten by each age class and specific numbers of each age), we see that 830 (that is, 912-82) or 91 percent of the food is left for deer when harvests are concentrated on the young age class. When only older animals are taken (as in Table 2), then substantially less food is left for the remaining population. Note that in this example, only 18 percent of the population is taken in both cases (usually more must be taken, about 30-35 percent, to avoid problems of insufficient high energy).

Table 2. Forage and harvest relations in a herd similar to that in Table 1. Here, harvest is concentrated on older animals as in an antlered buck harvest.
Age Class	Animals Present	% Harvest	Harvest	Forage (Tons eaten if Under-harvested)	Forage eaten by Harvested Deer
Fawn	500	0	0	456	0
1.5	100	8	8	91	9
2.5+	400	43	172	365	188
	1000		180	912	197

It is reasonable that with good management, deer may exist at half the density and twice the productivity - four times the energy flow in a herd.

The laws of energy rule deer herds. The herds need energy - consistently, without interruption, in sufficient quantities, and along with good supplies of protein. Any failures in any of these (due to weather, fire, drought, etc.) can result in lowered body size, small antlers, and a reduced number of fawns.

Over-use of plant by deer destroys the solar-energy-collecting and sugar-energy-storing base of the herd area. When native plants cannot be increased (as usual), then the population will decline normally. Predation is rare. The reasonable alternative is to manage human objectives, the food supplies, and the animals, all together. The objectives are as critical as the other factors. If, for example, large-antlered bucks are desired, 6 years of food energy must be traded off for them. This means that to get a 6-year old trophy buck (and the solar energy trapped by the wild plants needed for it), the other small, young deer that would eat that buck's food need to be removed. On average, in a balanced area, three 2-year old deer need to be removed to allow an area to supply the needs of a 6-year old trophy buck.

Future articles will describe the influences of cover on the deer energy budget.

This Web site is maintained by R. H. Giles, Jr.
Last revision January 17, 2000.