Study: Hunting and Trapping Coyotes May Not Improve Deer Survival

When hunting and trapping coyotes, this animal's adaptability makes it difficult. This trait is exacerbated by wolf DNA, making some coyotes slightly larger and likely more aggressive.

Study: Hunting and Trapping Coyotes May Not Improve Deer Survival

If you had to name one researcher who is the coyote/deer predation expert, it would be John Kilgo, who works for the USDA Forest Service.  In 2010, he published a paper suggesting coyotes could cause deer declines in the Southeast, in particular in South Carolina. Before we dive into how hunting and trapping coyotes may or may not aid in deer survival, first let's look at the data illustrating how coyote predation impacts deer herds.

Evidence from Kilgo's study shows the decline of the deer population in South Carolina at the same time the state's coyote population surged. In addition, deer recruitment at Kilgo’s South Carolina research site declined when coyotes increased there. Also a food habits study at the same site showed fawns were important food items for coyotes in the summer months.

Subsequent studies in other states in the Southeast also showed high coyote predation on fawns.

Later, Dr. Kilgo led a study where 216 fawns were radio-collar-tracked over seven years. The study found that coyotes killed a surprisingly high number of fawns. In fact, hunter mortality combined with coyote predation led to a significant decline in deer numbers in this large research area in South Carolina.

Photo: iStock

Data Suggesting Hunting and Trapping Coyotes May Not Work

One would think the logical way to solve this predation problem would be by hunting and trapping lots of coyotes.

Yet, Kilgo conducted a huge trapping study, removing hundreds of coyotes from a large area over three years. Common sense tells you that this would lower fawn mortality, but it didn’t. It turns out that about 1/3 of all coyotes are transients. They move about the landscape looking for a place with enough food to settle down as residents. Thus, when you remove a resident coyote, very soon a transient will move in and take that spot. This explains why, in this study, coyote numbers did not change much nor did fawn mortality. This was true even after several years of heavy trapping.

Intense trapping in the months prior to fawn drop would probably help, but that’s difficult and can be expensive for most landowners.

Adaptable Coyotes, Some with Wolf DNA, Complicate Wildlife Management

Coyotes have other attributes that make them difficult to control. For example, coyotes adapt well to new areas. We’ve got them in cities and in new areas where they’ve never been found before. This adaptability is exacerbated by the fact that coyotes in some Northeastern states, as far south as Virginia, have some wolf DNA. That makes them more adaptable, slightly larger and probably more aggressive than coyotes with no wolf DNA. This wolf DNA means they do better in forested habitats and eat more squirrels and other forest critters, but they still do well in agricultural areas too.

This photo shows a coyote sleeping on public transportation, a decidedly urban location. Photo courtesy of Port of Portland (via Louisiana Wildlife and Fisheries)

Some research from the western United States shows that coyotes may increase reproductive output in response to heavy trapping and shooting.

What about in the East?

Dr. Kilgo is in the middle of a big study on this issue in South Carolina. They looked at the reproductive tracts from 245 female coyotes trapped from 2010 to 2012. They trapped similar numbers of coyotes in each of those three years, indicating that population numbers didn’t change much — transients moved in.

Trapping Does Help By Creating a Juvenile Population

However, data showed more juveniles in the population after that trapping, and juveniles rarely breed.

When Kilgo just looked at the litter size and pregnancy rates for adult females, he found that there was a slight increase over the three years but — overall and because of the increased number of juveniles moving in — heavy trapping did not lead to increased reproduction. To impact coyote numbers, you have to impact juveniles in a large region. Why? Cecause high immigration rates of young transients render coyote populations extremely difficult to control.

Final Takeaways

So where does all this leave us? We now know that at least in Delaware, with no coyote predation in an area, lots of fawns still die from other natural causes. Maybe fewer predators would lead to less natural mortality. Maybe not. And we know that in South Carolina and other Southeastern states, coyotes really hammer fawns to such a degree as to lower deer numbers. In those areas since trapping doesn’t work well, the only solution may be to lower the number of does killed by hunters. Obviously, that won’t sit well with hunters.

We also know that in some deer states such as Ohio, Pennsylvania and West Virginia, coyotes cause about 10 percent of fawn mortality. Bears also cause about 10 percent, and bobcats another 8 percent or so.

However, deer numbers are still good and not showing any serious declines. Whether coyote numbers in such areas will go up and eventually lead to the situation found in some areas of the Southeast, is still unknown.

Yes, the coyote/deer situation is a fluid, changing one that seems to vary from one area to another. There are lots of variables and the need for on-going data collection. Most state wildlife agencies are aware of the situation and monitoring it.

My thoughts are pretty basic — I see the chronic wasting disease (CWD) problem as far bigger than the present coyote problem. For that reason, you’ll likely read more about CWD in future columns.

A related article examines the most common causes of death to deer fawns. It uses data to consider the real impact coyotes have on deer numbers.


Featured photo: Randy Roede


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