Study Shows How Coyotes Help Manage Deer Populations in the Southeastern U.S.

Adapted from article by Diane Banegas, U.S. Forest Service Research and Development

Forest Service researcher John Kilgo with fawn tracked by radio collar. Photo by U.S. Forest Service.
Forest Service researcher John Kilgo with fawn tracked by radio collar. Photo by U.S. Forest Service.

Coyotes have become a force in the southeastern U.S. that can no longer be ignored in deer management, according John Kilgo, a Forest Service research wildlife biologist. He and his colleagues arrived at that conclusion after spending the last decade studying coyote-deer interactions in South Carolina.

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 will help natural resource managers maintain deer populations at levels beneficial to ecosystem health and deer hunting, an economically important activity in the Southeast.

Kilgo and fellow scientists began studying predation on fawns in 2006 at the U.S. Department of Energy’s Savannah River Site near Aiken, 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 newborn fawns and monitored them to find out how many were being killed by coyotes. 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 cause the decline in deer populations observed in some areas.

“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. But 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.”

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 actually 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.

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.

“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.”

Read the longer Forest Service blog article.

Read Kilgo’s latest article on coyote predation on fawns and hiding cover.

For more information, email John Kilgo at jkilgo@fs.fed.us

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