Deer Overpopulation

Sebastian Indacochea

When one speaks of deer, it is usually referring to the North American Whitetail. Whitetail deer are one of the most prevalent game animals, found in every state except for Arizona and California. Around a hundred years ago, the population of this particular deer was about 500,000. That number has grown to an estimated 20 million. Many researchers believe that this increase results from continued human incursion into deer habitat, and the mismanagement of deer populations by forest and wildlife authorities that see hunting as the primary means of population control. The implications for local ecosystems are great and many proposals have been suggested to control the population.

The main impact that deer have on local ecosystems is over consumption. By browsing on tree seedlings, shrubs and climbers, deer tend to reduce stem densities, limit height and reduce foliage density. Stephen Budiansky describes an example of this in U.S. News and World Report. In his article, Budiansky discusses the studies of William Alverson, a professor at the University of Wisconsin who has studied old growth forests in Wisconsin for many years. Alverson found that the dominant hemlocks and white cedars have failed to reproduce. When asked what was causing the problem he stated, "the deer simply eat up all the seedlings that emerge. The changes due to deer are so slow that it's not obvious to someone driving by in a car, but at the regional level, hemlock forests are becoming rarer and rarer."

In the same article, Budiansky describes another issue concerning deer overpopulation. The deer herds in Irondequoit, New York stripped bare the local park and arboretum of exotic plants. The reason for this was a change in public policy. In 1978, the town officials banned hunting in the area, resulting in a dramatic increase of the deer population. Besides damaging cars and plants, the estimated herd of nearly 500 deer were slowly starving themselves by overpopulating the area. They had very low body weight, little body fat, and poor reproductive success.

What can be done to control the deer population? Many proposals have been brought forward. The expansion of the deer hunting season and allowing more does to be killed is a popular answer. This option poses many problems. The open hunting of does would leave many fawns motherless, significantly reducing the female population. As a result, many states passed laws restricting the amount of does that could be killed, contributing to the increase in population. Also, after hunting season ends, the remaining deer prosper due to less competition for food.

Introducing and maintaining existing natural predators, such as wolves and mountain lions, to the deer habitat is another measure suggested. These predators naturally keep the population in control. Due to hunting and human development, the number of predators has dwindled and, in turn, the deer population has increased.

A fairly new method of deer population control is the use of immuno-contraceptives. This process is non-lethal, making it popular with animal rights advocates. It causes the does to mount an immune reaction to a protein on the surface of their egg cells. The reaction kills the egg, preventing pregnancy. Unfortunately, administering this contraceptive is problematic; since the contraceptive would be destroyed in the gastrointestinal system, it must be given by injection. That entails shooting does with a dart from close range at least once a year. While relatively tame does are easy to hit, it's difficult to dart the reclusive ones, which form a larger percentage of the population.

Most likely, in the end, deer management will comprise of not one method, but a combination of many.  Each proposal, excepting perhaps stimulating predator populations, is a temporary solution because they are not sustainable.  A tech-fix is not a reliable resolution; a long-term solution that takes into consideration the cause of the problem as well as the effect is needed.

Budiansky, Stephen. "Deer, Deer Everywhere." U.S. News and World Report. 117.20 Nov.1994: 85

Ibid. 86

Return to ENVS2 homepage

Send message to Swarthmore College Environmental Studies

last updated 1/25/06