A study being considered by the Pennsylvania Game Commission board looking at the impact of predators on deer populations could provide some valuable insight, but it’s only part of the bigger picture, according to a researcher in New York.
Dr. Jacqueline Frair, an associate professor with the Department of Environmental and Forest Biology at the State University of New York, completed a five-year study in 2012 gauging the potential impact of coyote predation on deer populations. By tracking coyotes fitted with GPS collars across three study areas in New York, Frair’s research determined that deer do comprise part of the coyotes’ diet, but the canines may not be killing as many as people think.
“Coyotes do kill deer, but a lot less frequently than expected,” Frair said, adding there are other factors to consider before determining any impact.
“We know coyotes kill some fawns, but without studying survival from the deer’s perspective it’s hard to tell exactly what impact coyotes have. You need to look at other mortality factors that deer face - winter survival, roadkills, disease.”
Frair has conducted predator-prey studies with wolves and elk out west and used the same techniques for a similar study in New York. In 2007, 15 coyotes were fitted with GPS collars and their movements were tracked during the winter and summer months for two years each.
The collars recorded each coyote’s location every 20 minutes, and when Frair and her crew noticed several locations coming from the same area they backtracked the signal hoping to find a kill site.
“If they killed something big, it would take time to consume it,” she said. “It’s a more efficient way to find carcasses while there’s enough evidence left. It even worked really well in the summer finding fawn kill sites.”
Here’s what Frair’s study found:
- 86 carcasses were found in the winter, with 42 being scavenged deer that weren’t killed by coyotes. Three adult deer were killed by coyotes and they all had severe pre-existing injuries, such as broken joints.
- In the summer, fawns accounted for 33 of the 56 kill sites discovered, followed by woodchuck (13) and turkey (10). Four percent were goose and cottontail.
- Nine of the 15 collared coyotes killed fawns.
- Fawns were only vulnerable to coyote predation for a short time. Frair said all of the fawn kills occurred in June and declined sharply beginning in July.
Frair said the fact that the fawn predation occurred primarily in June is evidence of “predator swamping.”
“The does all drop their fawns in a short window so it kind of overwhelms the predator - coyotes. It’s an effective strategy because there’s too many fawns that the coyotes can’t kill them all,” Frair said. “By the 29th of June, when fawns were bigger and more mobile, the predation by coyotes dropped right off.”
Predator swamping is only effective where deer numbers are high enough to produce a significant number of fawns, Frair added. In areas where there’s few deer, it won’t work, she said.
A study proposed by PGC staff recently would be for five years with a price tag of $3.9 million.
Under the proposed study, three 150-square-mile blocks would be used. One would be a control area, another where black bear populations are reduced by as much as 50 percent over two years and the same thing is done with coyotes in the third. Then, for the following two years, both predators would be reduced in each of the two study areas.
Then, the study may start generating some answers to three questions:
- Does eliminating predators equate to an increase in deer numbers?
- By lowering the population of one predator, will the other increase and kill more fawns than before?
- Is there a way to control predators efficiently enough to increase deer numbers?
Frair was supportive of the proposed study because there hasn’t been much work done looking at compensatory predation on deer - when one predator declines and the other remains stable.
“Manipulating predator numbers is really the key thing that needs to be done scientifically,” Frair said. “These are critical studies that don’t happen because the price tags are so high.”
Frair cautioned the drastically reducing coyote numbers could backfire when it comes to impacts on deer. When numbers are significantly reduced, the coyote that remain have more resources to survive and produce larger litters.
“You could end up with more coyotes than you started with,” she said.
The concerns seen in Pennsylvania regarding coyote predation on deer were the same in New York before Frair began her study, she said, and after it was completed the mindsets really didn’t change.
“The public is clamoring to say the coyote is having too big of an impact on the deer herd, and I don’t think the best scientific studies will change that,” Frair said.
It’s possible that coyotes are being unfairly blamed for having a detrimental impact on deer herds. During her work in western states, the public’s focus was on the impact of wolves on elk and other predators like mountain lions were overlooked.
“Mountain lions are secretive and not often seen, but the canines are more visible and people hear them,” Frair said. “Coyotes can and do kill deer. No doubt about it. I think it’s unfair to say they’re decimating deer herds. I don’t think coyotes are taking out adult breeding deer and we just don’t have the evidence to say coyotes are bringing down the carrying capacity for deer.”