If you live in the suburbs of the Northeastern US like I do, on any given day you might be able to look out your window and see a herd of deer like the one pictured above. In my neighborhood in particular, I am surprised if a day goes by where I don’t see any.

In 1930 the US white-tailed deer population was down to about 300,000. Today, estimates of how many there are range as high as about 30 million. That’s a 1,000-fold increase in less than 100 years.

What would an ideal number of white-tailed deer be in the US? Scientists estimate the average carrying capacity is about 8 deer per kilometer. The current average? Up to 100 deer per kilometer.

The shift in the white-tailed deer population can be attributed to many factors. In the 1920s the species was actually nearing extinction due to overhunting before government protection programs and national parks sought to save it. You could say that they succeeded. Unfortunately, a number of factors are now leading the deer population to spiral out of control. These include:

No predators. Wolves, cougars, and grizzlies, which all once preyed on old, sick, and newborn deer, are now extinct in most states, and much of their former habitat is gone. However, the increase in human population will not stop the deer because…

Deforestation actually helps the deer. The white-tailed deer is a species that flourishes in “edge” habitats: that is, habitats along the edges of forests and roadways, as well as newly-planted lawns. This is why they have been so explosively successful in the suburbs. Which also means…

Hunting rates are going down. On average, about 6 million deer are killed each year by hunters, though this number is decreasing. By contrast, the deer population will double every other year under ideal conditions; the latest estimate suggests that 12 million fawns were born after the last hunting season. And this number will keep increasing because…

Due to the fact that they preferentially graze on disturbed or edge habitats, white-tailed deer populations naturally fluctuate. As such, they have evolved few methods of self-regulation (such as birthing fewer fawns in crowded conditions).

So there are a lot of deer and the population is still growing. The impacts this has are not just the annoying ones that I see every day (deer poop everywhere, deer carcasses all over the roads, destroyed gardens, and the occasional deer attack).

Deer in the US eat 15 million tons of vegetation each year, which costs about $248 million in damage to crops and landscaping in the Northeast alone. About 150 people per year are actually killed due to car collisions with deer. Furthermore, deer carry deer ticks, which can transmit lyme disease to humans.

But the impacts are not limited to us. Native ecosystems are bearing the brunt of the damage. A study on one forest in Pennsylvania found that over half of all plant species diversity had vanished thanks to hungry deer. Other studies suggest that deer prefer eating native to exotic plant species, which facilitates the spread of invasive plants.

This can lead to a cascade of effects on other animal species. Nesting bird populations drop due to the loss of certain tree species (the deer like to eat the new saplings). Insect species, particularly caterpillars, may lose their food sources. Conversely, biting flies and other parasites that prey on deer will increase.

What we should do about the deer overpopulation has been a highly divisive issue in the US; specifically between those who favor lethal vs. nonlethal methods. There is limited success with methods such as fertility control, but these successes are mostly found in closed populations (i.e., fenced in or isolated) and take a long time to take effect.

Lethal methods also have their pros and cons. The possibility of reintroducing wild predators of deer in parts of the US where they are now extinct is often raised and just as often vetoed, given that the bulk of the deer population lies smack dab in the middle of the suburbs.

Similar concerns are raised when people bring up hunting; furthermore, hunters must be advised to take does rather than trophy bucks or they will not significantly affect the population. Studies have shown that controlled hunting programs are effective over small areas, but the effects are mixed over larger ones.

While people argue over what the best way to manage deer is, the population continues to grow and grow, leading to an increase of diseases (such as epizootic hemorrhage disease, which can also spread to livestock) and starvation.

With deer populations going well over carrying capacity in many areas, the risk of population crashes grows. While a crash- which dramatically decreases the number of animals- sounds like it might be a good thing in this case, crashes can be catastrophic. In one famous reindeer crash on St. Matthew island, 95% of individuals died in a single winter.

That, however, is the worst-case scenario, and since few deer populations are so constrained, the more likely one is that deer populations will eventually strike a kind of limbo- not increasing very much but still heavily overpopulated, and constantly on the brink of starvation.

In this case, what is the correct thing to do? The longer we wait, the more damage is done, not just to people, but to the local ecosystem as well. But methods like contraception take several years to really show positive effects, while hunting has to be carefully managed in order to be effective. And this isn’t even bringing in the “moral” aspect of hunting versus nonlethal methods. Yet either way, many, many deer are going to die, and the only way to improve their- and our- quality of life is to dramatically reduce their population.

This isn’t the first time I’ve written about the issues with animal overpopulation- check out my post on rodent plagues. I’ve also written an article about deer with fangs.

To see a list of all animal articles that I’ve written, head to the Nonfiction section of this site.

References

Alverson, W.S., D.M. Waller, and S.L. Solheim. 1988. Forests too deer: edge effects in northern Wisconsin. Conserv. Biol. 2: 348–458.

Brown, T. L., Decker, D. J., Riley, S. J., Enck, J. W., Lauber, T. B., Curtis, P. D., & Mattfeld, G. F. (2000). The future of hunting as a mechanism to control white-tailed deer populations. Wildlife Society Bulletin, 28(4), 797-807.

Eschtruth, A. K., & Battles, J. J. (2009). Acceleration of exotic plant invasion in a forested ecosystem by a generalist herbivore. Conservation Biology, 23(2), 388-399.

Horsley, S. B., Stout, S. L., & DeCalesta, D. S. (2003). White-tailed deer impact on the vegetation dynamics of a northern hardwood forest. Ecological Applications, 13(1), 98-118.

Insurance Institute for Highway Safety. 2009. Deer-vehicle collisions: no easy solutions but some methods work or show promise. Advisory No. 31.

Iowa State University, 2012. Epizootic hemorrhage disease in deer and cattle.

Kilpatrick, H. J., & Walter, W. D. (1999). A controlled archery deer hunt in a residential community: cost, effectiveness, and deer recovery rates. Wildlife Society Bulletin, 115-123.

Patterson, B. R., & Power, V. A. (2002). Contributions of forage competition, harvest, and climate fluctuation to changes in population growth of northern white-tailed deer. Oecologia, 130(1), 62-71.

Peek, L.J., and J.F. Stahl. 1997. Deer management techniques employed by the Columbus and Franklin County Park District. Ohio. Wildl. Soc. Bull. 25: 440–442.

Piesman, J. (2006). Strategies for reducing the risk of Lyme borreliosis in North America. International Journal of Medical Microbiology, 296, 17-22.

Rooney, T. P., & Waller, D. M. (2003). Direct and indirect effects of white-tailed deer in forest ecosystems. Forest Ecology and Management, 181(1), 165-176.

Rooney, T. P., & Dress, W. J. (1997). Species loss over sixty-six years in the ground-layer vegetation of Heart’s Content, an old-growth forest in Pennsylvania, USA. Natural Areas Journal, 17(4), 297.

Rooney, T. P. (2001). Deer impacts on forest ecosystems: a North American perspective. Forestry, 74(3), 201-208.

Roseberry, J. L., & Woolf, A. (1998). Habitat-population density relationships for white-tailed deer in Illinois. Wildlife Society Bulletin, 252-258.

Rutberg, A. T., & Naugle, R. E. (2008). Population-level effects of immunocontraception in white-tailed deer (Odocoileus virginianus). Wildlife Research, 35(6), 494-501.

Seagle, S. W., & Close, J. D. (1996). Modeling white-tailed deer< i> Odocoileus virginianus population control by contraception. Biological Conservation, 76(1), 87-91.

U.S. Department of the Interior, Fish and Wildlife Service, and U.S. Department of Commerce, U.S. Census Bureau. 2006. National Survey of Fishing, Hunting, and Wildlife-Associated Recreation.