EXCLUSIVE: Thinking Slowly About Coyote Predation on Deer

After reading the title, some of you might have thought: When it comes to coyotes, the only thing I want to slow down is my breathing as I squeeze the trigger.

While I’ve had similar thoughts in the past, and have taken a number of coyotes from the deer stand and on the trapline, allow me to explain. “Thinking, Fast and Slow” is a best-selling book by Nobel Prize winner Daniel Kahneman. In his book, he explains the human tendency to use our instincts, past experiences, personal bias and emotions to make most decisions. He considers this thinking fast. On the other hand, we have the ability to slow our thinking and approach the same topics from a more deliberate, logical perspective.

Coyote predation on white-tailed fawns is high in some areas and almost nonexistent in others.

Like many of you, I used to think fast when it came to the threat coyotes posed to my most cherished pastime, deer hunting. Coyotes kill and eat deer. I kill and eat deer. One of us has to go and I know it ain’t me! But as I became more involved in the latest research concerning coyote predation on deer, my think- ing slowed and I was surprised by the resulting shift in my perception. That said, my goal for this article is to present you with some evidence from my own and others’ work to encourage you to think slowly about the effects of coyotes on whitetail populations and what we should (or shouldn’t) do about it.

PREDATION CONCERNS
Allow me to begin by making it clear that, without question, coyotes significantly impact deer populations in some areas. If that weren’t the case, we likely wouldn’t see the multitude of magazine and online articles devoted to the topic, or the numerous fawn survival studies implemented by state wildlife agencies in the recent past. This undoubtedly raises some concerns. The whitetail hunting industry supports a wide variety of small and large businesses, rural communities and state wildlife conservation agencies.

In addition, private landowners invest significant time and money toward improving conditions for whitetails on their properties. Perhaps most importantly, deer hunting is a cultural and deeply personal experience for many of us.

However, what I’ve come to realize is that it’s important to not stop at the question of whether coyotes kill deer. From a management perspective the critical information is this: How many deer they kill; if predation rates differ among properties; and the effects of this mortality on the overall deer population. If the answers to these questions cause concern, the next logical step is to determine what tools might be used to combat coyote predation and how effective they are.

SURVIVAL AND RECRUITMENT
So, let’s start with the question of how many deer coyotes kill. Undoubtedly, coyotes do attack and kill some adult deer. You can confirm this with a quick online image search. However, many of my colleagues and I believe that coyote predation on adult deer is the exception, rather than the rule. Collectively, we’ve used radio or GPS tracking equipment on hundreds, if not thousands, of adult deer and there is little evidence to suggest that coyotes regularly kill adult whitetails. Thus, this article will focus only on the effects of coyotes on fawn survival and recruitment.

The question isn’t whether coyotes hunt and eat deer, especially fawns; they do. The questions to ask are: How many deer they kill; if predation rates differ among properties; and the effects of this mortality on the overall deer population.

Probably the best starting point for this discussion is the work done by Dr. John Kilgo and his colleagues in western South Carolina. From 2006-09 they monitored 91 fawns outfitted with tracking collars. When a fawn died, the researchers used a variety of techniques to ascertain the cause. At the end of the study, 56 fawn mortalities were attributed to coyote predation. To put that in perspective, only 14 additional fawns died as a result of all other mortality causes combined.

Certainly those numbers are cause for concern, right? Yes. If coyotes killed a similar proportion of fawns across the whitetail’s range, we’d be losing more than 60 percent of our annual fawn crop to coyote predation. However, the goal of this article is to get you to think slowly about coyotes and deer, and I mentioned earlier that a number of recent studies have focused on this topic. Dr. Kilgo’s study likely happens to be one of the most frequently discussed online and in print, not only because it was well designed, but also due of its shocking results. So let’s look at findings from a couple of similar studies to gain additional perspective.

Interestingly, an Auburn University study led by Dr. Stephen Ditchkoff from 2006-10 in South Carolina generated different results. Of the 219 fawns included in the study, only 14 were killed by coyotes. Despite these drastically different results, this site was only a little over a 90-minute drive from Dr. Kilgo’s! However, an important difference is that predator control is practiced on the site that hosted the Auburn study. Although this might make your fast-thinking side want to come to the conclusion that coyote control is the answer, hold that thought for just a second.

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RESULTS CAN VARY
Prior to beginning my work at Auburn University this past year, I conducted my graduate and post- doctoral work at the University of Georgia. During that time, I led a coyote research project on two study sites in central Georgia under the direction of Dr. Karl Miller. We documented fawn recruitment on both sites for two years before and two years after successive coyote removals using professional trappers. The sites were only about 5 miles apart along their closest boundaries.

Interestingly, fawn recruitment on one of the sites was about 50 percent greater than that on the other before we did any trapping. We had evidence to suggest the difference in fawn recruitment between sites was due to differences in coyote predation rates, although we couldn’t be completely certain. However, this offers additional evidence to suggest that coyote predation on fawns can vary quite a bit, even among properties within the same county.

Since discussion of additional results from similar studies all across the country is beyond the scope of this article, suffice it to say that this trend plays itself out from one study to the next across the whitetail’s range. Coyote predation rates on fawns vary significantly over space and time, due to a wide array of complex, interact- ing factors researchers are only just beginning to understand.

Now, remember my earlier assertion of the most relevant questions surrounding coyotes and deer from a management perspective. We’ve covered information on how many deer (mostly fawns) coyotes kill and how that predation rate can vary, but as deer hunters and managers, what we’re really interested in is how that affects the overall population. Luckily, a couple of groups of researchers have already tackled that question. It turns out that in all but the worst cases, fawn losses to coyotes can be compensated for by reducing or eliminating doe harvest.

HOW DOE HARVEST AFFECTS
FAWN RECRUITMENT RATES

The minute details of these studies are numerous, but the inset chart (Figure 1) presents a simplified model of how deer populations change in response to different fawn recruitment rates and levels of doe harvest. Briefly, the recruitment rate is the number of fawns (per doe) born every year that actually survive until fall. While most mature does give birth to twins, a recruitment rate of one is considered “good” in most of the whitetail’s range. As far as doe survival, in the absence of significant hunting mortality, approximately 90 percent of does survive on an annual basis.

This graph illustrates how deer populations change in response to differ- ent fawn recruitment rates and the level of the doe harvest.

The figures represent the estimated number of does on a 640-acre property over a 10-year period, start- ing with a moderate deer density (about 30 deer/mi2) and a 2:1 doe-to- buck ratio, which is not uncommon. I’m focusing on the doe population here because they are the reproductive “engines” of the herd. In Scenario B we see that when the recruitment rate is one fawn/doe (black line), even with an annual harvest of 30 percent of the doe population, the herd grows from approximately 15 to 30 does over a 10-year period. However, if recruitment decreases to 0.4 fawns/ doe (blue line), the same level of doe harvest results in a population decline from around 15 to fewer than five does over a 10-year period. In my experience, a recruitment rate of 0.4 fawns/doe is not unusual on a property with a high rate of coyote predation. Of course, the other recruitment rates presented in the figure yield a result somewhere in the middle.

At first glance, these results seem devastating. But now let’s jump over to Scenario A. Even with a recruitment rate of 0.4 fawns/doe, the population increases over a 10-year period when no does are harvested. It’s hard to see because of the scale of the figure, but the simple model actually
indicates a two-fold increase in the doe population over 10 years under this scenario. On the other hand, if we increase the recruitment rate in Scenario A back up to 1.0 fawns/doe, which is not unusual in the absence of significant predation, the population explodes to around 400 does over a 10-year period. In the real world, this population growth rate would slow over time as habitat quality decreased in response to deer overabundance.

However, this incredible rate of population growth is the reason state agencies use doe harvest to maintain or decrease deer abundance in certain areas. On the other hand, it’s easy to see why deer harvest was limited to buck-only hunting during the early days of deer hunting, when populations were still recovering.

Limiting doe harvest is the most reliable, cost-effective method of combating fawn losses to coyotes

The take-home point is that deer populations can withstand high rates of fawn predation, provided that doe harvest is reduced accordingly. Limiting doe harvest is the most reliable, cost-effective method of combating fawn losses to coyotes. However, situations exist where annual doe survival is lower than normal, perhaps 70 to 80 percent, even when does are completely protected from hunting. In addition, there are hunters and landowners who enjoy the opportunity to harvest a number of does annually, myself included.

If either of these conditions apply to a given property, you might want to consider coyote removal. When it comes to coyote removal, our fast thinking side says: For every coyote I kill, I’m undoubtedly saving one or more fawns. Unfortunately, that’s not necessarily the case. Early research on the effects of coyote removal indicated that intensive coyote trapping could increase fawn recruitment on a property by 100 to 200 percent. However, most of these studies involved only a single year of trap- ping.

A more recent study conducted by Kilgo on the same South Carolina site found that fawn survival did, in fact, increase follow- ing the first year of coyote removal. But following a second and third year of intensive trapping, the benefits of removal diminished. In fact, during one of the removal years, fawn survival was the same as during the pre-trapping period. These findings led the researchers to conclude that intensive coyote removal has only a modest positive effect on fawn survival.

The results from my previous work in Georgia were similar. On one site, fawn recruitment nearly doubled following the first year of coyote removal, but decreased back to the pre-removal level after the second year of trapping. Interestingly, recruitment on our second study area, a few miles down the road, was high throughout the entire study period. In fact, our records indicate that the recruitment rate was similar to what it was prior to arrival of coyotes on the site! This despite that our estimates of coyote abundance were similar between sites.

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WHAT’S THE BOTTOM LINE?
What conclusions can we draw from these findings? It appears intensive coyote removal can have a positive effect on fawn survival or recruitment. But its effectiveness might vary significantly among years and from one property to another. To clarify, intensive removal involves the removal of at least 75 to 80 percent of the coyotes occupying a given property.

This is typically only achieved through the use of an experienced trapper over an extended period of time. It is highly improbable that the occasional harvest of a coyote from the deer stand will have any notice- able effect. In fact, the results from the aforementioned studies likely represent a best-case scenario of what landowners might expect in terms of increases in fawn numbers following coyote control. Professional trappers were hired to remove coyotes for several months each year on our study areas.

Many logically conclude the reason for these observations is that coyotes compensate for removal by increasing their reproductive output, but recent research shows that might not be the case. In fact, coyote numbers may rebound following removal much faster than reproductive output would allow, thanks to a segment of the population known as transients.

Recent GPS tracking studies have shown that about 30 to 50 percent of coyotes do not have a territory. They basically bounce around the landscape, covering tens of thousands of acres in a given season, likely looking for a vacancy. These individuals likely serve as population “founders” following the removal of coyotes from an area. While there’s no clear answer as to how quickly these animals fill a vacant area, the results of the afore- mentioned removal studies indicate that it’s less than a year.

CONCLUSION
We’ve covered a lot of information very quickly, so let’s recap:

1) Coyote predation on fawns can decrease fawn recruitment, reducing a deer population’s growth rate.

2) Coyote predation on fawns is high in some areas and low to non-existent in others, even across small geographic scales.

Coyote hunting is awesome but the most effective means of predator management over a long period is sustained trapping.

3) Even in areas where fawn predation rates are very high, hunters can usually compensate for fawn losses by reducing or eliminating doe harvest.

4) If reduction or elimination of doe harvest is undesirable, hunters may consider coyote removal, but it’s not guaranteed to work every year or on every site.

5) Coyotes quickly repopulate areas, even following intensive removal. Thus, continued trapping might be required to maintain high fawn recruitment rates on an annual basis.

What’s the best course of action? First and foremost it’s more important now than ever for deer hunters and managers to know the current status of the deer herd where they hunt. A wide variety of techniques, including formal trail-camera surveys, can be used to gather this information. In some cases I’ve worked with landowners who want to control coyotes when, in reality, they have a deer overabundance problem on their hands.

Clearly defining the goals and objectives for a property, and getting an idea of its current status in relation to those objectives, can prevent management errors and misallocation of resources.

If this process reveals suppressed recruitment, evaluate other management alternatives prior to coyote removal. For example, overpopulation can suppress reproductive output. This should either be resolved via population reduction, or increasing habitat quality. Improving habitat quality for deer can have the added benefit of increasing the amount of available cover for fawns, potentially reducing their exposure to coyotes and other predators.

If deer overabundance or habitat quality aren’t limiting factors on your property, you might consider inten- sive coyote removal. However, make sure you don’t go into a removal program thinking it’s a silver bullet, and realize that you might invest significant time and money with minimal or temporary returns on that investment. On the other hand, each property is different, and although research gives us some insight into what we might expect given a certain set of circumstances, it is not perfect.

I hope you’ve learned something by spending some time thinking slowly about coyote predation on deer. The intent of this article isn’t to discourage hunters from taking coyotes. To be honest, there’s a huge container full of traps and supplies taking up space in my garage right now. Trapping, like deer hunting, is a time-honored tradition and can be a valuable population management tool. But most things in life are complicated, and the dynamics between coyotes and deer are no exception. That said, I am optimistic that you’re now more prepared than ever to tackle any challenges they might bring your way.

— Dr. Will Gulsby is a professor in the School of Forestry and Wildlife Sciences at Auburn University.

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