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Researcher uses neutering in managing coyotes

UW researcher uses neutering in managing coyote population

Oct 16, 2013 - From staff reports

Marjorie MacGregor wants to manage coyotes through better chemistry.

For the past four years, MacGregor, a University of Wyoming doctoral candidate in the Department of Zoology and Physiology, has headed a chemical castration or neutering research program using captive male coyotes. The hope is that the program can eventually be used in the wild to control coyote numbers and reduce depredation while, at the same time, not alter the animal's natural behavior.

"Some ranchers just want to kill them. And some environmentalists say leave them alone," MacGregor says. "I'm trying to work the middle ground. We're trying to manage coyotes, both for a natural ecosystem and for wildlife-human conflicts. We have to find a balance. That's very difficult in Wyoming."

For years, ranchers and farmers here and in other states have killed coyotes that kill and feed upon their domestic sheep and lambs. In addition, "coyote contests" are organized for people to shoot the animals as a means to reduce the population.

In spite of these lethal control measures, the coyote population has continued to increase, if not thrive, across the United States. Their habitat range has expanded beyond just Western states to the entire continental United States, as well as Alaska and Canada, MacGregor says. Research has shown that coyotes have "compensatory mechanisms" for when they are under lethal attack. In effect, females increase their litter size and begin reproducing earlier.

"We don't know how they know, but there are a lot of studies that have shown it," MacGregor says.

Coyote testing

The 13 male coyotes used for UW research are kept at two undisclosed facilities off campus. Coyotes, ranging in age from one and a half to eight years, are divided into three groups. One group receives 47 milligrams of a drug called deslorelin acetate, which is available for use as a short-term contraceptive for domestic dogs, MacGregor says. The coyotes are injected with a contraceptive implant one time. The time-released implant is placed under the skin and between the shoulder blades.

The second group receives the drug, but in a slightly different formulation. For coyotes in the first two groups, sperm counts hit zero after four months, MacGregor says. The third group, a control group, is left alone.

Every two months, MacGregor and her team of graduate students collect blood samples and semen counts from the coyotes. The drug has proven effective, with some male coyotes' sperm not having reproduced in three years, MacGregor says. In other cases, sperm counts in some coyotes returned to their prior levels within six months.

"We want to control reproduction, but not decrease the fitness of the animal," MacGregor says. "It's like if you take your dog to the vet. You want to know a drug given to it won't hurt it."

In this case, MacGregor says she doesn't want to alter the animal's behavior, only alter its ability to reproduce.

Coyotes, in the wild, only produce sperm approximately six months out of the year.

"They're seasonal breeders," MacGregor explains. "Then, they shut down for the rest of the year."

As part of her research, maintaining natural coyote behavior is crucial, she says, because a male and female coyote mate for life, stay together and maintain territories.

"Females mate once a year," MacGregor says. "We want her to think she has a fine functioning male. If we're changing the behavior of the male, we don't want that."

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