In South Carolina, Coyotes Not a Threat to Adult Deer

Study finds coyotes kill fewer adult female deer than expected

Although coyotes kill large numbers of fawns, they are not always a threat to adult female deer. Photo by Steve Hillebrand, U.S. Fish and Wildlife Service, courtesy of Wikimedia Commons.
Although coyotes kill large numbers of fawns, they are not always a threat to adult female deer. Photo by Steve Hillebrand, U.S. Fish and Wildlife Service, courtesy of Wikimedia Commons.

In parts of the northeastern U.S., white-tailed deer populations have ballooned. Not so in parts of the southeastern U.S., such as South Carolina, where the statewide deer population has been declining for about 12 years.

“In the Southeast, coyotes often prey on white-tailed deer fawns,” says U.S. Forest Service research wildlife biologist John Kilgo. “There are also reports of coyotes attacking and killing adult female deer.”

Kilgo has been studying white-tailed deer for years, and recently led a study on deer survival patterns. The study was published in the Wildlife Society Bulletin, and took place at the Savannah River Site, a 310 square-mile nuclear reservation in South Carolina. The study involved 138 female deer that were fitted with radio collars to track their movements. The deer were monitored from 2006 through 2013.

Each year, 87 percent of the deer that Kilgo and his colleagues were studying survived. “Some studies have reported yearly survival rates as low as 57 percent,” says Kilgo. “Compared to deer in other parts of South Carolina, the deer at our study site are long-lived.”

During the course of the study, 30 of the 130 deer studied died. Hunting season had the most impact on deer survival, as 43 percent of deer that died did so during November and December. “Although harvest rates were low, harvest was the most frequent cause of deer mortality,” says Kilgo. Collisions between deer and vehicles were also a significant cause of death, and were responsible for 27 percent of the deer mortality.

The scientists were unable to determine a cause of death for 23 percent of the deer mortalities, although 6 out of 7 of these deaths occurred during summer, so diseases or other causes could have killed them. Theoretically, it is also possible that coyotes killed some of these deer.

However, the overall results strongly suggest that coyotes prey very infrequently, if at all, on adult deer. “Even if all unknown mortalities were caused by predation, the overall effect of these mortalities on annual survival was low,” says Kilgo. “It doesn’t appear that coyotes are a major threat to the adult deer we studied.”

“Coyotes are known to kill adult deer in some parts of the Southeast, but they did not have a significant impact in our study,” says Kilgo. “However, previous studies have shown that coyotes do kill significant numbers of fawns.”

At the Savannah River Site, only 22 percent of fawns survive. Most of them are killed by coyotes. Because of the low fawn survival, wildlife managers had already reduced harvest limits for adult female deer, so although hunting was a primary cause of deer mortality, the overall number of deer harvested by hunters was low. In areas where hunting limits and coyote predation are both high, limiting harvest could have a greater impact.

Controlling coyote populations is expensive, and the study suggests that adult female deer will not benefit from it, at least at the Savannah River Site.

Read the full text of the article.

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

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