This is the only article of its kind on this website, one that I cannot accurately determine the validity of. I wrote this article after having first heard about a notion that the abundance and quality of food can affect reproductive rates among a population. To this day I am unsure of whether this is true. Still here is the article written from the perspective that diet can determine birth numbers. See what you think, but I recommend further research before committing to either perspective.
Hunting as a Method of Population Control
By Jeremy Alcorn
Among the variety of reasons provided for the continuation of hunting we find an appeal from the standpoint of conservation presented in the form of population control. While there is information regarding the effectiveness of hunting towards the goal of population control, there is also research that would suggest otherwise. This information lends a degree of plausibility to the notion that population control methods such as hunting constitute more of a risk than initially thought.
Deer herd populations are controlled by a number of variables. For the purposes of this article we shall be examining the effects of population numbers based on the availability of food and the male to female ratio. Briefly examined is the severity of winter casualties.
Winter Attrition
The first variable we should explore is one that we will return to a number of times in the course of this article. In climates that experience winters where vegetation is adversely affected deer herd populations drop because of a process referred to as “die-off” [1]. Winter die-off is where the old and/or weak segments of a population succumb to the elements such as cold and starvation. Winter die-off helps to alleviate food shortages for the surviving members of a population and has the effect of eliminating weaker genetic lines. By eliminating some members of a population whose genetic code causes them to be among the least adaptable, future members will be better able to survive. This is what is referred to as natural selection and it insures that the future population will be equipped with the traits that are best suited for survival.
Food Availability
Food, and its availability, is another factor that relates to the number of deaths as well as births. Predictably, a lack of food can cause deaths from starvation, but another factor may be far more important in controlling populations.
When food is scarce the birth rate of a population will decrease [3; 4]. This is due to biological changes brought about by malnutrition. Malnutrition causes male deer to become less virile than what is present during nutritionally adequate years. As for the obverse gender, female deer when undernourished will encounter reduced or, in extreme situations, complete cessation of ovulation (This is in keeping with studies of malnourished humans as well) [1]. Both of these occurrences limit the number of births and help to keep the population in balance with the availability of food.
Male to Female Ratios
Now let’s briefly address the dynamics behind the male to female ratios amongst deer populations. The natural outcome of deer births rest around fifty-percent male and fifty-percent female, that is, an equal number (1:1) of males and females are born each year [1]. The birth ratio when it varies usually favors more male births than females [3]. However, this difference is usually not significant.
Birth ratios are important because during mating season a single male deer will mate with as many females as are receptive to him. If there were more females than males the birth rate would increase each year. This is especially important considering that some females, depending on the quantity and quality of food, will give birth to more than one fawn. A given area of land can only provide food for a limited number of deer. So it is advantageous that half of a population be male, because more females will lead to more births and, subsequently, less food.
The Negative Effects of Hunting
The natural 50/50 birth ratio is often offset by the actions of hunters either intentionally or accidentally. As we will see below, some believe the ratio of female to male deer in the wild is 8:1 respectively [2]. Hunters who participate in big game hunting involve themselves in the search for a trophy. I know hunters who continually seek to “bag”, or kill, a big buck; often they succeed. In the case of deer hunting, a trophy is a male deer with a large number of antler points or tines (which branch off of the animals main antler beams) than what is normally seen.
Because many hunters would like to kill large bucks, states try to limit this by issuing certain types of permits. These permits are “either-sex” which allows a hunter to choose which sex deer to kill, or “antlerless” meaning a hunter can only kill a deer with no antlers or antlers coming in under a specified height. Many hunters possessing an either-sex permit set out to kill primarily male deer. In fact, local research has determined that of the either-sex permits issued, 87% of those were used for male deer [8]. To overcome this states issue antlerless permits to some applicants. However, even with these permits in hand; hunters sometimes kill male deer because they were too young to have developed antlers, and were resultantly mistaken for females. Again, local research indicates that of the antlerless permits issued, 29% of those are used for male deer rather than females [8]. This is perfectly legal, but it can further skew the population ratio. Also, not all antlerless permits are filled every year leaving to chance the situation of too few female deer being killed. Given the hunter’s desire to kill a trophy buck, the killing of young bucks when attempting to kill females, and the plausibility that female deer will be under killed each year; it is easy to concede that the population can be thrown off balance. In Illinois, for instance, the states leading employed biologist Dr. Paul Shelton stated, "During the 1999 season we didn't take as many does as we should have" [5]. This statement indicates that indeed, at times female deer are not killed in the numbers needed.
Implications of Skewed Sex Ratio
When more female deer survive than do males, the subsequent year(s) will produce more fawns in the spring. Add to this factor the decrease in food usage caused by hunting season deaths, winter die-off, and nonhuman predation, and a population increase will inevitably follow. Peter Muller, board member of Wildlife Watch, Inc bases his example on a 80:20 sex ratio (80 female: 20 males). With such a ratio present Muller contends that,
“Nature's mechanisms that adjust the population to the browse will now miscalculate and cause an overpopulation. Based on 50-50 ratio, a herd of 400 will produce a maximum 50-animal net gain assuming a 100 animal winter die-off and 150-fawn increase from the remaining 150 does. Based on an 80-20 ratio, a 400 animal herd will produce a 140 animal increase, assuming again a 100 animal winter die-off, but this time 240 does will give birth to 240 fawns instead of 150 does giving birth to 150 fawns. With the ratio distorted at 80-20, the population will increase to 540 instead of 450” [1].Two things can happen as a result of this. The first is that a die-off greater than normal may result either from starvation or disease. The second, and far worse, scenario is that the increased herd population survives only to further inflate its population for the upcoming mating season.
From the Field
Certain historical accounts lend credence to the second scenario stated above. Consider Missouri’s conservation efforts at increasing deer populations. Around the turn of the 20th century Missouri’s deer population consisted of “395 deer in 23 counties” [6]. Missouri was in danger of losing one of its species. Because the populations were severely below natural levels Missouri soon banned hunting (unregulated hunting was a reason for the decline). In 1944, Missouri implemented a “bucks only” hunting season in an effort to increase the herd’s population [7]. This allows more births in the spring than if the females were killed. Due in part, to this special hunting season, Missouri now is experiencing a population of around 750,000 deer [6].
Hunting is no doubt central in affecting population but with an increasing body of research it is seen by many as a dangerous gamble. It is true that the immediate problem of population control is resolved. For instance, the Missouri Department of Conservation estimates that 200,000 deer are killed annually by some 400,000 hunters [7]. While this seems as if hunting has served a vital purpose in reducing herd numbers, some believe that the stage is set for a population increase. It seems as if the second scenario is sound given that deer herd populations almost everywhere are increasing.
Conclusion
By the preceding account, if hunting controls population at all, it serves to elevate population levels to the eventual point of starvation on a wider scale than what occurs naturally. Given the natural propensity for deer herds to biologically control their population numbers; the strain humans place on those reproductive tendencies serves to exacerbate the dynamics of herd demographics while increasing population numbers simultaneously. Until society comes to realize the folly of its conservation efforts (i.e. hunting), the unnatural trend towards increasing population numbers will likely become more of a problem than it is today. Hunting, then, is not a utility for thinning out deer herds but more of a liability to their health and longevity.
Works Cited
1 - Muller, Peter. 1998. The Committee to Abolish Sport Hunting. 27 November 2002
2 - In Defense of Animals. 2002. In Defense of Animals. 25 November 2002
3 - Marchington, Larry. 2002. University of Maryland: Agriculture and Resource Economics Department. 27 November 2002
4 - Humane Society of the United States. 2002. Humane Society of the United States. 1 December 2002
5 - Potts, Brenda. 2002. Illinois Game and Fish Magazine. 28 November 2002
6 - Missouri Department of Conservation. 30 January 2002. Missouri Department of Conservation. 24 November 2002
7 - Missouri Department of Conservation. 25 April 1996. Missouri Department of Conservation. 24 November 2002
8 - Alcorn, Jeremy. “Project Deep Woods: A Survey of the 2004/2005 Deer Season.” VeganVanguard.com. 4 Jan. 2005. 4 Jan. 2005
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Posted/Updated: 5/01/07
