How coyotes affect deer

In order to get a better understanding of the coyote-whitetail relationships, biologists at the Savannah River Site then examined the results of an intense coyote removal effort in the same areas they studied fawn predation.
How coyotes affect deer

Seven years ago, Charles Ruth gave little thought to the effect of coyotes on deer populations. As the deer project leader for the South Carolina Department of Natural Resources, he fielded calls from hunters concerned about the state's growing coyote population and what seemed like a decrease in deer. There's no question coyotes eat fawns, but Ruth figured the predators couldn't possibly keep up with South Carolina's booming deer population. Coyotes simply weren't anything to be concerned about.

"I'm a Southeast deer biologist. I was trained in the Southeast and I've always worked in the Southeast," he says. "Coyotes just weren't part of the equation for much of my career, so when I started examining coyotes and deer, I got my information from Western biologists in states that have always had coyotes. Deer and coyotes seem to get along just fine in those Western states, so I assumed the same thing was happening here."

But then Ruth participated in a six-year in-depth study. The first leg, which lasted three years, examined coyote predation on fawn mortality. Researchers captured does and placed transmitters in them that fell out when they gave birth. They then captured the newborn fawns and fitted them with tracking collars and monitored their survival rates. If the collar stopped moving for a set period of time, indicating the fawn had died, researchers went to the site and determined the cause of mortality.

The results were astounding. Researchers involved in the study, which took place on the grounds of the Savannah River nuclear facility site, knew coyotes ate deer fawns. They had no idea they ate so many. As it turned out, 80 percent of the fawns that died from all causes were killed by coyotes.

Other studies have found similar predation rates. One conducted in Alabama by researchers at Auburn University attached radio collars to seven fawns. Only one survived, and five of the six mortalities were likely caused by coyotes. Another Alabama study found that coyotes accounted for more than half of all fawn mortalities.

Kill All The Coyotes

In order to get a better understanding of the coyote-whitetail relationships, biologists at the Savannah River Site then examined the results of an intense coyote removal effort in the same areas they studied fawn predation. The first year, three trappers removed a total of 169 coyotes, with trapping efforts running right up until the fawn birthing season. The trappers were given financial incentives to stretch out their efforts so they didn't catch their quota right away, which would have allowed coyotes from surrounding areas to fill the void.

"We were pleased to see that fawn survival doubled that spring," notes Ruth. "That was the response we were expecting."

Trappers caught another 160 or so coyotes the second year, but a curious thing happened. Ruth says it didn't appear to have much of a result on fawn recruitment.

"It's like we did nothing. Fawn recruitment was essentially right where it was before we started trapping coyotes," he recalls.

Trappers removed 160 more coyotes the following winter, and Ruth says fawn survival was "somewhere in the middle."

"We aren't really sure what's going on, although we haven't finalized all the data yet. There are many more factors related to fawn recruitment and survival than just predation, but I can say that if you are concerned about coyote predation on your deer herd, trapping is the best solution," he says. "The trouble is that it can take a lot of effort, as we found out, to catch the number of coyotes you need to catch in order to have an impact on the population. The average deer hunter isn't going to have the time or resources to do that."

In other words, the random shooting of the occasional coyote will likely have no noticeable effect on fawn recruitment rates. That's not to say shooting every coyote you see won't help at all, but South Carolina deer hunters shoot about 30,000 coyotes each year. Still, the state's deer population has declined by about 30 percent since 2002. Part of that can be attributed to aggressive efforts by the agency to increase the overall harvest, but there is no doubt coyotes are a factor in that decline. That's why Ruth and his fellow biologists at the SCDNR are recommending changes to the state's deer management program. To him and other deer biologists, managing coyotes isn't the answer. Instead, wildlife managers will have to instead change the way they manage deer.

Manage Deer, Not Coyotes

"We've already cut back on the number of antlerless quotas for our deer management assistance program (DMAP) by about 15 percent, and we've cut back on either-sex days in parts of the state," he says. "Many of our DMAP cooperators were already taking steps to reduce antlerless deer harvest, so I think hunters are beginning to understand how to better manage their deer with the presence of coyotes."

Wildlife managers on Alabama's Fort Rucker also cut back on the deer harvest by eliminating the antlerless deer season and limiting hunters to two bucks per season. Additionally, those bucks must have at least three points on one side. Those changes are the direct result of increased coyote predation. Ruth says he plans on recommending additional changes, including measures that would decrease the buck harvest. The final decision rests with state legislators, who have the final say in the DNR's management recommendations.

The good news is that South Carolina's deer herd is still healthy and success rates among all hunters still hover around 70 percent. Ruth says there is no cause for alarm yet. However, he cautions that the growing presence of coyotes will likely have far-reaching management implications for state wildlife agencies throughout the Southeast. Coyotes are abundant throughout whitetail country, but their numbers seem to be growing in the East and Southeast. That means other states will likely be forced to change the way they manage their deer herds as well. Until then, however, hunters might want to make some changes of their own. Just as DMAP cooperators in South Carolina have backed off on the numbers of antlerless deer they are taking, concerned hunters in other regions can do the same thing, says Quality Deer Management Association education and outreach coordinator Kip Adams.

First, remember that just because you have coyotes in the area doesn't necessarily mean they are having an impact on your deer herd. That's why Adams says it's important to know if your fawn recruitment is below a sustainable level as it relates to the current harvest level. The best way to figure that out is through old-fashioned field observations. Simply counting the number of bucks, does and fawns you and other hunters see and keeping a careful tally can help you determine if your fawn population will sustain your current population level of adult deer. A one-to-one fawn-to-doe ratio is ideal. Many states don't come close to that, but still maintain a sustainable deer population that meets hunter demands through the adjustment of antlerless harvests. If fawn populations go down, killing fewer does will help maintain current population levels.

"Once you figure out the fawn-doe ratio, you can adjust your antlerless harvest to meet your population objectives," notes Adams, who adds, "Reducing the number of antlerless deer can certainly help, but there are other steps hunters can take to help fawn recruitment."

He recommends improving fawning cover by encouraging the growth of thick underbrush, which gives fawns a place to hide and, thus, a better chance of escaping the jaws of a coyote or bear. A Pennsylvania fawn predation study found that survival rates were higher in farm country than in the study area's mature forests, which typically have little or no undergrowth.

"Either selective logging or clear-cutting will encourage new growth, which in turn creates great fawn cover," says Adams. "It's also good for other species of wildlife, including adult whitetails."

Adams agrees with Ruth that killing the occasional coyote will have little effect on deer populations. Removing a few predators from the landscape only creates a void that others from surrounding areas will fill. Numerous studies have found that at least 75 percent of coyotes must be removed from an area in order to have an impact on fawn survival. No hunter or hunt club can achieve that rate through recreational hunting alone.

"Focus on the things you can have an impact on, like habitat and reducing the harvest of antlerless deer," says Adams. "Coyotes are here to stay, and the sooner hunters realize that we can't shoot or trap our way out of them, the quicker we can focus on things that we can do that will make a difference."


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