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Hunting
Coyotes Plus Doe Harvest Could Lead to Predator Pit
New research at Fort Rucker shows heavy predation of fawns.
 
By Daryl Kirby
Originally published in the November 2011 issue of AON
 
Coyotes may be killing enough deer to keep herds from recovering from overharvest.
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Deer managers and hunters now know for certain coyotes in Alabama and other southeastern states are taking a bite out of fawn numbers. Top deer researchers, including the team at Auburn’s Deer Lab, have studied fawn mortality and found survival is significantly lower than it used to be. Coyotes are the primary fawn killer.

A recently published study on fawn survival at Fort Rucker showed there was hardly any survival to speak of. At Fort Rucker and in other recent studies in the Southeast, fawn survival ranged from 20 and 23 percent, and that is translating to low recruitment rates of 0.2 to 0.25 fawns per doe. Recruitment rate is the number of surviving fawns per adult doe in the pre-hunt population. In a healthy deer herd, recruitment rates should be 0.6 to 0.8., and the fawn survival rates should be at about 50 percent.

A decade ago, you’d have been scoffed at for saying coyotes kill a significant number of fawns in the Southeast, but it’s a fact backed by the latest research. Now, there is growing evidence coyotes are actually limiting deer populations. Even more shocking is that fawn-eating coyotes, when combined with overharvest 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 to AON 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 Alabama and other southeastern states was that it was nearly impossible for hunters to kill too many does. Either-sex days were liberalized, and limits for antlerless deer were practically deemed unnecessary in the minds of many deer managers.

Now it appears coyotes are a wildcard that could dramatically change the deer-management game on some tracts of land.

“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.


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 Dale and surrounding counties in the Wiregrass region of southeast Alabama. Fort Rucker has a rich history of great hunting and fishing, thanks in large part to on-staff biologists and good management practices.

Like many tracts of land in the mid to late 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 the 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 reduced antlerless harvest, the herd never recovered as it should have. The highest harvest in subsequent years was 189 deer in 2000. Last season only 50 deer were killed at Fort Rucker.

Something significant was going on. The wildcard was at work — coyotes.

On Aug. 6, Auburn University published a graduate thesis written by Angela Jackson titled “Survival Estimates of White-tailed Deer Fawns at Fort Rucker, Alabama.” Angela and other researchers, under the direction of Dr. Ditchkoff and with the help of Fort Rucker biologists and volunteers, radio-collared and monitored 14 fawns in 2009 and 2010. The low deer density that made Fort Rucker a prime location to study fawn survival also posed a problem. There were so few deer they couldn’t get enough for a larger sample size.

Does were trapped with cannon nets over areas baited with corn. The does were sedated, and vaginal implant transmitters were inserted. When a doe gave birth, the transmitter was expelled, and researchers could move in and find the fawn, which was fitted with a telemetry collar.

According to Angela’s thesis, “Of the 14 fawns, only three survived to 6 months of age. Six of seven predation events were attributed to coyotes based on examination of bite patterns and remains left at the site.”

The study estimated the probability of fawn mortality at Fort Rucker due to coyotes to be 65 percent.

“This study, like other recent studies in the Southeast, has found that low fawn recruitment seems to be driven by greater levels of coyote predation than originally believed,” Angela wrote.

The Fort Rucker study was the first in the Southeast to look at both fawn survival rates and coyote densities.

“Presenting both of these estimates creates a baseline for comparison with future studies and could help to elucidate our understanding of the interactions between these two species,” Angela wrote.


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 Alabama 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. I pretty much felt that same thing, and 15 years ago we would have been on cruise control,” 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, the wildcard, 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 at least for discussion and study.

“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.’ The scary part from a deer-management perspective is that hunters could go too far back the other way and not shoot any does.”

Hunters were the first to sound the alarm that they were seeing drastically fewer deer. As far back as 2006, the Conservation Advisory Board (CAB) heard enough complaints from hunters that coyotes and doe days were the subjects of a discussion during a CAB meeting.

“Some of them were seeing considerably lower deer numbers, and I think others were just seeing less deer,” Steve said. “The one thing I’ve always said is, the whole reason we increased doe-harvest numbers was to drive deer populations down. If our goal was to reduce a population by 20 percent, then we should see less deer, No. 1. But No. 2, if you reduce a deer population by 20 percent, your deer sightings probably go down by 50, 60 or 70 percent, and most people don’t realize that. So it’s difficult to gauge hunter observations.

“Three things we’ve documented,” Steve said. “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. But if our recruitment rates are .5, .6, .7, then we can shoot some does. 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. Here in Alabama, you don’t want to do it in August and September — you’ll under-represent the fawns. Go out in October and November and throw a camera out there on a trail,” Steve said.

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 much. You’ll have to deal with the coyotes. Fighting back against coyotes is something we covered most recently in the June 2011 issue of AON, and we’ll continue to provide information on hunting and trapping coyotes.

Deer management always seems to be evolving. In Alabama, the rapid expansion and growth of coyote numbers in our deer woods has changed the game yet again.



Support The Deer Lab

Auburn’s Deer Lab is largely dependent on financial support from private individuals and organizations. Donations have provided support for important deer research that would not be possible without their support. Please visit <http://deerlab.auburn.edu> for information on how you can help support important deer research in Alabama.
 
 
 
 
 
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