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Study Concludes Coyotes Help Manage Deer Population in Southeast U.S.

Diane Banegas
Forest Service Research & Development
October 7, 2015

The wily canine thrives in its adopted region but questions remain about its impact on other species

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Coyotes, a species native to the western U.S., gradually colonized the southeast during the latter half of the 20th Century. Their migration coincided with a decline in overabundant deer populations in some areas.

“Coyotes generally do not prey on adult deer in the southeast, but they were known to prey on fawns,” Kilgo said. “We wanted to know if this predation had become a big enough force to regulate deer populations.” His research results will help natural resource managers maintain deer populations at levels beneficial to ecosystem health and deer hunting, an economically important activity in the southeast.

The scientists began studying fawns in 2006 at the U.S. Department of Energy’s Savannah River Site in Aiken and Barnwell counties, South Carolina. The study was a cooperative effort between the Forest Service’s Southern Research Station, South Carolina’s Department of Natural Resources, and the Savannah River Site. The scientists attached radio collars to fawns and monitored them for several months to find out how many succumbed to the coyotes and whether the total number killed could explain the declining deer population.

Vaginal implant transmitters, or VITS, in the does signaled fawn births, allowing the scientists to find newborn fawns and put radio-collars on them. They tracked about 40 fawns each year for several years. The collar transmitters emitted a “mortality signal” when the collar was immobile for four hours. When the scientists arrived at the scene, they determined the cause of death and in cases of predation, collected DNA from saliva found on the fawn to determine if the predator was a coyote or another species such as a bobcat.

The scientists tracked 216 fawns over seven years. The number of fawns killed by coyotes was much higher than expected, and the predation level was high enough to affect deer populations but not high enough to control populations by itself.

“The combination of fawns killed by coyotes and deer taken by hunters together caused the downward trend,” Kilgo said. “Before coyotes arrived in the area, hunting was barely able to keep up with expanding deer populations. In that respect, the coyotes are a good thing. If populations decline so much that managers have to suspend or shorten a deer season, it won’t be considered a good thing, especially by hunters.”

Asked why hunters couldn’t simply start hunting coyotes to help deer, Kilgo replied that coyotes can be hunted and trapped but in addition to being wily, they are highly prolific and very adaptable to their new region. Coyotes eat almost anything, vegetation as well as meat. They eat everything from roadkill to rabbits to wild fruits. Hunting and trapping usually aren’t very effective at controlling their numbers.

Coyotes began migrating eastward throughout the latter half of the 20th Century. Once restricted to the western plains, they now occupy most of the continent and have invaded farms and cities, where they have expanded their diet to include squirrels, household pets and discarded fast food. Land-use changes in the U.S., a growing human population, and a remarkable ability to adapt to new environments and conditions encouraged coyotes to expand into new habitats and thrive, while other predators faced with similar pressures dwindled and faced extinction.

Humans transporting coyotes to the southeast as hunting stock also sped up coyote establishment in the region. Coyotes were trapped in western states, illegally transported to the southeast, and released into pens for hounds to chase; inevitably, some escaped into the wild where, in typical coyote fashion, they adapted and thrived in the new habitat. The practice has pretty much stopped, but the coyote is here to stay. The coyote nuisance factor is a real one: crops and livestock are destroyed or damaged, household pets are killed, people even worry about their children, although coyotes in the Southeast have no record yet of attacking humans, as they have in some western states like California.

Some biologists have suggested that beefing up the undergrowth in southern forests would make it more difficult for coyotes to find fawns, thereby allowing more to survive. On the contrary, Kilgo’s research showed that fawns living in areas with dense understories were even more likely to be taken by coyotes. “It seems that dense undergrowth may just serve as a message to the coyotes that the brush is hiding something,” Kilgo said. The scientists also extensively trapped coyotes to see if fawn survival was any better, but the results were mixed. They concluded the practice would be too expensive and labor intensive for most private landowners to adopt, given such uncertain benefit to fawns.

“The best way to ensure that more fawns survive is to shoot fewer does during hunting season because that means more fawns will be born the next spring,” Kilgo concluded.

He and his research colleagues are now studying coyote populations themselves to get a handle on their population density. They extract DNA from coyote dropping, or scat, collected from across the area to identify how many individual animals were sampled and model their findings to determine population size.

The Savannah River Site, a national laboratory, is 300 square miles and managed by the Forest Service for the Department of Energy. Such protected sites become a haven for wildlife. The coyote population there increased throughout the 1980s-1990s, but it has remained stable since then. “They’ve reached the carrying capacity of the area,” Kilgo said.

The scientists may have answered their questions about coyote-deer interactions in the southeast, but Kilgo’s coyote research is far from done. He plans to study how they interact with other species in the region; in particular, he wants to know if wild pigs, which are also not native to the southeastern U.S., are influencing coyote populations. Pig carcasses typically remain in the woods when they are killed for population control, and this food source may increase carrying capacity for coyotes.

“We already know when it comes to canines such as wolves, coyotes, and foxes, the big dog wins,” Kilgo said, citing the example of coyotes leaving Yellowstone Park after wolves were reintroduced there.

“Management strategies need to accept coyotes as a permanent presence in the southeast because we can’t eliminate them. Instead, we need a better understanding of their effects on other species and the surrounding habitat,” Kilgo said. “When it comes to coyotes, our questions still exceed our knowledge.”

For more information, see these related publications: