Coyotes Could Drive Deer Into “Predator Pit”

Researchers confirm impacts on deer can be serious. If you're killing a lot does, pay attention to fawn survival rates.

Daryl Kirby | May 15, 2012

Coyotes may be killing enough deer that populations can’t recover from overharvest.

Deer managers and hunters now know for certain coyotes in Georgia are taking a bite out of fawn numbers. Top deer researchers studying fawn mortality are finding survival rates significantly lower than they used to be, and coyotes are the primary fawn killer.

Studies in the Southeast are finding only 20 to 25 percent of fawns are making it, and recruitment rates are 0.2 to 0.25 fawns per doe. Recruitment rate is the number of surviving fawns (5 to 6 months old) per adult doe in the pre-hunt population. In a healthy Georgia deer herd, recruitment rates should be 0.8 to 1.0, and the fawn survival rates should be more than 50 percent.

GON first sounded the alarm that coyotes were impacting deer populations when we published a two-part series the summer of 2006. Hunters had been scoffed at for the mere mention of coyotes killing a significant number of fawns. Those who dared to post messages on Internet forums saying their deer numbers were way down because of coyotes were ridiculed and told they needed to learn how to become better hunters if they weren’t seeing deer.

For at least eight years, GON has been flooded with complaints from deer hunters that deer numbers had dropped drastically in some areas. The annual Rate Your Deer Season survey went from year after year of mostly Excellent and Good ratings to mostly Fair and Poor ratings. Last year, one-third of deer hunters who responded to the survey rated their season as Poor. Yet, any mention that coyotes might be to blame was met with skepticism or even derision.

Two leading researchers, retired WRD biologist Kent Kammermeyer and UGA professor Dr. Karl Miller, were sources for those 2006 GON articles. Their comments—although tentative and guarded at that time—saying coyotes might be limiting and even lowering deer numbers in some areas gave credibility to the coyote alarmists.

Now, six years later, the impact of coyotes on deer numbers is a fact backed by solid research. Even more alarming is that fawn-eating coyotes, when combined with overharvest by hunters of female deer, may be causing a deer-management black hole called a predator pit.

In the predator-pit scenario, if a deer population is reduced past a certain point by hunter harvest, it will then get hammered even more by coyotes to a point the population is so low the coyotes won’t let the deer herd recover.

Dr. Steve Ditchkoff, an Auburn professor and a top whitetail researcher who heads up Auburn’s respected Deer Lab, talked about the predator-pit concept, which has come to the forefront as researchers examine fawn mortality at several locations where deer populations are usually low.

“We’re guessing at this point—trying to make an educated guess—at what is going on and why. This predator-pit model really describes, I think, what we’re seeing,” Steve said. “If a predator pit is occurring, essentially what it’s telling us is we can harvest does, and that’s an important part of a deer-management program, but we just have to be careful not to push it ‘too hard.’ I put too hard in quotes because I don’t know how to describe that any better.”

The general consensus in southeastern states has been that it was nearly impossible for hunters to kill too many does. Either-sex days have been liberalized, and limits for antlerless deer were practically deemed unnecessary in the minds of many deer managers. In 2002, Georgia’s Wildlife Resources Division (WRD) pushed for doing away with having a limit on antlerless before stubbornly compromising by only raising the limit from eight to 12 deer per season.

Fort Rucker Wildlife Biologist J.B. Bruner holds one of 14 fawns radio-collared during a fawn mortality study at the military property. Only three of the 14 fawns survived to 6 months of age.

Now it appears coyotes are a wildcard and are dramatically changing the deer-management game. It is almost a certainty this predator has already had a significant impact on some tracts of land where hunter harvest of deer has been very high.

“If you keep a deer population above a certain threshold level, the deer population will rebound back to high deer numbers,” Steve said. “But if you push it below a threshold level, then coyotes are able to pull it down further to a second point of equilibrium.”

Once the deer herd gets to that point—mired in a predator-pit scenario—reducing hunter harvest isn’t enough to bring the deer population back up. The coyotes won’t let the herd recover.

Dr. Karl Miller is a professor of wildlife ecology and management at the University of Georgia’s D.B. Warnell School of Forest Resources and one of the country’s foremost whitetail experts. Karl was one of the first to begin extensive coyote research in the mid 2000s when he began to suspect coyotes were impacting deer numbers.

“I don’t think in a lot of places we’ve gotten to that [predator pit scenario] yet, although in one study we saw some of that. On a 2,000-acre property in northeast Alabama they did a reduction in their deer density, and they expected to see this rebound that you typically see. They didn’t see it. They just ended up with fewer deer. We went in and did a coyote removal, and we saw recruitment rates—fawns entering the population at 5 to 6 months of age—jump from .4 before the coyote removal up to 1.2 fawns per doe. In another study we did coyote removal in southwest Georgia, and it went from .45 to .9 fawns per doe.

“On these study areas coyotes were having a significant impact of reducing recruitment by half or maybe even more than half. If that’s the case, and you’re running a fawn recruitment rate of .4 fawns per doe, it’s going to take that population a while to recover. Typically across the state, I’d say we’re running recruitment rates of about .8 to about 1.0 in the absence of coyotes.”

The Fort Rucker Situation

Too many deer, time to whack some does. That was the thinking in the late 1980s at Fort Rucker, a 63,100-acre Army facility located in southeast Alabama. Fort Rucker has a rich history of great hunting, and like many tracts of land in the mid 1980s, the deer herd at Fort Rucker flourished a bit too much. Low weights and heavy parasite loads indicated an overpopulation of deer. Antlerless harvest was increased, and dog drives were allowed so more deer could be killed. It worked.

The record harvest at Fort Rucker was 633 deer in 1987, which was the first year hunters killed more female deer than male deer. Five years later, the harvest had dropped to 338 deer. Two years later, in 1994, the harvest was down to 162 deer, and that’s when antlerless harvest was reduced and dog drives were stopped. The next season only 74 deer were killed, including only three female deer. But even with hardly any antlerless harvest, the herd never recovered as it should have. The highest harvest in subsequent years was 189 deer in 2000.

In 2010, only 50 deer were killed at Fort Rucker, despite prime habitat and years of hardly any antlerless harvest. Something significant was going on. The wildcard, the game-changer was at work—coyotes.

Auburn University’s Deer Lab published a study last August on the Fort Rucker deer situation. Researchers found very poor fawn survival rates, and coyotes were the primary predator. The study estimated the probability of fawn mortality at Fort Rucker due to coyotes to be 65 percent. The study, like other recent studies in the Southeast, found low fawn recruitment was driven by greater levels of coyote predation than originally believed.

This chart shows the dramatic drop in the deer population, and how it remains low even after doe harvest was eliminated.

How We Got Here

In the late 1980s, deer populations were at all-time highs after making a remarkable comeback. Restocking efforts in the 1950s worked, and enforcement of game laws limited the harvest of does.

Too many deer meant it was time to kill some does, and deer management in Georgia and other southeastern states quickly went from little antlerless harvest to hunters killing about as many and in some cases more does than bucks. About the same time, the concept of quality deer management (QDM) took off. Fewer deer meant better quality.

“With the QDM push, it did a good job of educating the hunters about the need to harvest does,” Steve said.

Deer management in the late 1990s and the next decade seemed to be on auto pilot—the herd had been restored, liberal doe days and limits allowed for plenty of antlerless harvest to keep overpopulated areas in check, and bigger bucks were being grown.

Hunky-dory in the deer woods.

“Cruise control is a real good description of where we were,” Steve said. “But the thing we started to push was harvest does, harvest does, harvest does, not realizing that you possibly could push populations over the edge.”

Coyotes have changed the game. The idea that it’s possible to kill too many does may have seemed ludicrous to some deer managers, but it’s a concept that’s now on the table even for biologists who have been digging in their heels in dismissing the theory.

“We’re realizing it is possible to push a population down too far in some cases,” Steve said. “We don’t know if this is common, but there have been a couple of populations that have been studied that show that you can push a population to the point where you have very low recruitment rates, and as a result that population has a very difficult time rebounding.

“Now we’re essentially saying, ‘Whoa, you can shoot too many does,’” Steve said.

The 2012 Southeast Deer Study Group Meeting was held Feb. 26-29 in Destin, Fla. Coyotes were the primary topic during this gathering of the region’s top deer researchers.

“The entire theme was, ‘What do we need to do in the face of this new predator?’” Karl said.

“I gave a keynote address, and basically it was that we need to start thinking about our recruitment rates,” Karl said. “The idea we used to preach of having an intensive doe harvest to maintain these deer population may not be applicable. The ball game has changed. We have a new predator here, and that predator in some areas is reducing recruitment rates, and in some areas there are probably very significant reductions. We have to be more cognizant of what our recruitment rates are and adjust our doe harvest accordingly.”

Karl said state wildlife agencies are recognizing the impact of coyotes, but they haven’t gone as far as adjusting their harvest or bag limits.

“I think the onus is on the people who are actually managing the deer herds where they are hunting,” Karl said. “My take-home message is it becomes very important for the hunters and managers of their particular property to start monitoring what they see as far as recruitment rates.”

Steve summarized the situation: “Three things we’ve documented… one, coyotes are here. Two, we’re documenting greater rates of predation on fawns. Three, we’ve documented if you reduce predator numbers, you can get increases in recruitment rates. I don’t think that’s a solution to the problem, but it may play a role in management in some form or fashion.”

As hunters who also want to best manage their property, what do we do about the coyote wildcard?

“I think what this means is, take a more conservative approach, No. 1. But two, I think it requires us monitoring our deer population a little more carefully. More specifically, what I’m saying is we need to understand what recruitment rates are. If we have recruitment rates that are like .2 to .25 fawns per doe, then we need to be very, very, very cautious. Hunters have considered themselves managers for years. They read the QDM magazines, watch TV and try to do everything—well, they just need to do a little bit more.”

That little bit more should focus on getting a handle on the recruitment rate of deer on their property. Fortunately, there’s a tool many landowners already have that is helpful for determining recruitment rates—trail cameras.

“Camera surveys can provide a decent estimate if done at the right time and the right way,” Steve said. “Essentially, you can’t do it on bait. If you run your surveys on bait, depending upon the time you do it, your numbers can be significantly inflated or may significantly under-represent the number of fawns that are out there. Do them on trails. You start to get an unbiased estimate of what’s out there.”

In Georgia, the prime months for using trail cameras to estimate your recruitment rate are July and August. Karl agreed that camera surveys were the best way for the average landowner or hunting-club manager to learn about their recruitment rates.

“Look particularly at how it changes from year to year,” Karl said. “Also keep up with hunter observations—record the number of fawns and the number of does seen with observations scattered across the property. Record that data, and compare it from year to year. Also record lactation data in October and November. Does that are dried up then likely lost their fawns early. If a doe stops lactating, it doesn’t just mean she lost a fawn; it means she lost both fawns if she had two. A 70 percent lactation rate probably means only a ballpark figure of 50 percent fawn survival.

“If your recruitment rate goes down, what do you do? For many hunters, they can’t afford to do intensive coyote trapping. They’re going to have reduce the doe harvest,” Karl said. “If you get down to a .4 recruitment rate, the percent of the population you can remove every year drops significantly. I hear from hunters who just say the deer aren’t out there anymore, and in some cases that very well may be the case.”

Getting a feel for the recruitment rate will help guide your antlerless harvest, but that’s only half of the equation. If your property has already fallen into the predator-pit scenario, reducing your doe harvest isn’t going to help. You’ll have to deal with the coyotes.

Fighting back against coyotes through trapping is something we discuss on page 80 of this issue of GON. Hunting coyotes is another option, and we’re about to hit a prime time to have an impact by taking out some coyotes—the fawning season. Hunting with fawn calls targets coyotes that are actively hunting and feeding on fawns, and each one of these fawn killers that is removed could result in better fawn recruitment on your land this season.

Karl’s current research centers on improving recruitment rates by removing coyotes. They’re working a research project on 5,000 acres of B.F. Grant and Cedar Creek WMAs.

“The data is coming in right now. I don’t have the definitive numbers yet, but we’re seeing a response in recruitment in response to the coyote removal there,” Karl said.

How many dead coyotes does it take to make a difference?

“It’s not that many; it really isn’t,” Karl said. “There’s a lot we don’t know about coyotes right now—social behavior and their dispersion across the landscape. Killing a transient coyote that’s moving through an area might not do anything, but if you have a territorial pair out there that are feeding pups, killing them will. They’re out there grabbing protein packets. Think about it… they can go grab a bunch of cotton rats or mice or rabbits, or they can grab a fawn. It behooves them to go out and actually look for fawns. Fawns are not that hard to catch, especially if you don’t have good fawning cover.”

There is no longer any doubt the rapid expansion and growth of coyote numbers in the deer woods has changed the game yet again.

“This is the new face of deer management in the Southeast,” Karl said.

“We’ve got the coyote. And we’re going to have to deal with them.”

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