Immigration and Reproduction Complicate Coyote Control Programs

coyote

Coyotes arrived in the Southeast relatively recently. “Beginning in the early 20th century, coyotes started moving eastward,” says John Kilgo, a research biologist with the U.S. Forest Service. “But they weren’t recorded in South Carolina until the late 1970s.”

From an evolutionary perspective, they’ve been incredibly successful. They have become quite common in the Southeast.

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Kilgo, here with a radio-collared, tranquilized coyote, has studied coyote-deer interactions and fawn survival on the Savannah River Site. Photo courtesy of John Kilgo, USFS.

For example, at the Savannah River Site, a U.S. Department of Energy nuclear reservation in the coastal plain of South Carolina, coyotes were first observed in the mid-1980s. Today, there are as many as 1,100 coyotes in the 310-square mile area.

Some wildlife managers and municipalities are interested in controlling coyote populations.

“Coyote populations have an almost uncanny ability to recover from such efforts,” notes Kilgo. “There are two possibilities to explain that: increased reproduction or increased immigration.”

Kilgo and his colleagues tested both possibilities. Data came from an intensive coyote trapping program that ran from 2010 to 2012 – part of an effort to protect white-tailed deer fawns from coyote predation.

The researchers analyzed the data to examine pregnancy rates, litter sizes, and fecundity. Those findings were published in the Journal of Wildlife Management.

In the two years following the trapping, the scientists didn’t find significant changes to litter sizes, pregnancy rates, or overall fecundity. They did see coyotes breeding at younger ages, even juveniles. “That’s not enough to explain population recovery,” says Kilgo.

In the West, control programs have long been believed to stimulate coyote reproduction – more pups, breeding at younger ages, and an increase in the proportion of the breeding population. Less is known about coyotes in the Southeast, but they do behave differently in some ways, including – as Kilgo and his colleagues discovered – reproduction.

“We saw some measures of reproduction increase modestly,” says Kilgo. “However, the overall reproductive output actually decreased.”

Kilgo also contributed to a companion study that addresses coyote immigration. Elizabeth Kierepka led that study, which was also published in the Journal of Wildlife Management.

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Coyotes are difficult to study in the field. Genetic analysis tools can provide information that helps scientists and managers understand how coyote populations recover rapidly from control efforts. Photo by Matt Knoth.

The researchers analyzed genetic samples collected during trapping. They ran simulations to understand how trapping had affected various genetic characteristics.

If wandering coyotes, or transients, had moved into the Savannah River Site from surrounding areas, the genetic makeup of the remaining population could change.

Some coyotes are wanderers. “There are individuals – and not an insignificant part of the population – that are transient,” says Kilgo. “They may move 100 miles or more, then settle down for a year. Then they pick up and go again.”

Coyotes also wander when they’re young. Whether male or female, coyotes that are about a year old often leave the area where they were born. “They can cover great distances, crossing a state or two,” adds Kilgo.

The researchers saw genetic evidence of recolonization by transient coyotes. After trapping, they found weaker signs of familial structure and philopatry. This result indicates that transient immigrants had moved into territories vacated by the trapped coyotes.

Collectively, the two studies suggest that coyotes can recover from intensive trapping through a combination of reproduction and immigration.

“Our study suggests that intensive control programs may only reduce coyote populations for a few months,” says Kilgo. “There seems to be a very large regional pool of immigrants ready to move in as soon as a resident coyote is removed. Wildlife managers, landowners, and anyone interested in reducing coyote-human conflicts should be aware that this situation makes it extremely difficult to control coyote numbers for any length of time without ongoing effort.”

Read the full text of the reproduction article.

Read the full text of the immigration article.

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

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