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Birth Control Darts Fired At Idaho Wild Horses To Slow Herd Growth

Andrea Maki
Copyright 2014

Federal wild horse specialists from Idaho and Oregon have been trained in how to shoot birth control darts into the rumps of wild horses.

The technique could soon see wider use to slow the growth of wild mustang herds. The federal government estimates more than 40,000 wild horses roam the Western range.

Field staff from the Bureau of Land Management in Challis, Idaho, and Ochoco National Forest in central Oregon traveled to the non-profitScience and Conservation Center in Montana to learn about a wildlife contraceptive called PZP.

Center director Jay Kirkpatrick said the birth control can be injected in wild horses via a small dart fired from an air gun.

"If you can get within 50 yards of the horse, you can dart it," Kirkpatrick said. "You don't have to capture it. It's easy on the horse. You don't chase them around with helicopters or wranglers or vehicles."

Late this spring, the BLM's Challis Field Office and volunteers with a local nonprofit injected five free-roaming mares in the initial deployment of the field darting technology in the Northwest.

"We're looking to expand [darting]," BLM wild horse specialist Kevin Lloyd said. "Even if we can slow population growth a little bit, it can be useful to us."

A Challis-based nonprofit that advocates for wild horses said it covered the BLM's expenses to get the fertility control program going. Wild Love Preserve founder Andrea Maki wrote in an email that her group is pleased to have facilitated a "collaborative" way to keep wild horses on their home turf.

Lloyd noted some of Idaho's wild horses avoid people, so it could be "problematic" to get close enough to use a dart gun. Mares need to be re-injected annually for maximum effectiveness.

"The way I look at it, we need to use everything that is available to us," Lloyd continued. He expects other techniques like periodic roundups and removals will continue to be used to prevent overpopulation.

Credit Andrea Maki / Copyright 2014
Copyright 2014
Wild mare darted in right rump in May 2014.

Kirkpatrick said wary animals can be brought within darting distance with bait or water traps. "That's a technique that is being used as we speak," said the scientist from his office in Billings, Montana.

Another logistical challenge with darting is keeping track of which wild mares have been treated and then finding them again to deliver an annual booster in subsequent years. Kirkpatrick explained range managers often recognize individual wild horses on sight. Photo identification has also proved viable in herds with variation in coat colors and patterns. If a horse has been previously caught in a roundup it may have a visible brand.

Kirkpatrick said he has worked on the PZP contraceptive for decades. His center produces the doses used by BLM, five tribal wildlife departments and some private wild horse preserves. He called PZP very safe for animals and environment.

"Biologically it is pretty simple. It doesn't interfere with behavior or the endocrine system. All it does is block fertilization," Kirkpatrick said. PZP is a pig-derived protein that stimulates antibodies when injected, which interfere with fertilization.

Wild horse herds reproduce at rates of up to 20 percent per year. Lloyd said fertility control darting would be more attractive to range managers like himself if the drug lasted longer, on the order of five years even.

Although the Ochoco National Forest sent three wild horse specialists to train on the technology this year, a spokesman said those Forest Service workers have no plans at the moment to fire any birth control darts into rumps. "We would have to propose a project and vet it through the public" first, said Ochoco spokesman Patrick Lair in Prineville.

Lair said the national forest's Big Summit wild horse herd has grown to nearly double the target size of 55-65 horses identified in a herd management plan. "It's a big question what is to be done," Lair said.

The Ochoco herd probably descended from horses which escaped or were purposely freed by pioneer miners and ranchers. The same is true for central Idaho's wild horses according to an environmental assessment prepared by the BLM. The horses have few natural predators and get blamed for resource damage by other forest and range users.