Wild horse population crisis: Birth control with PZP or roundups by the BLM.

Wild Horses Are Symbols of Freedom, but They’re Also Invasive Pests

Wild Horses Are Symbols of Freedom, but They’re Also Invasive Pests

The state of the universe.
April 16 2014 11:49 PM

Wild Horse Crisis

What’s the best way to control an invasive species: Round them up or shoot them?

a group of wild horses.
Ada Inbody (left) and Patricia Hatle walk toward a group of wild horses near Cody, Wyo. Inbody and Hatle control the horse population near Cody using a dart gun loaded with birth control vaccine.

Courtesy of Warren Cornwall

MCCULLOUGH PEAKS, Wyo.—The view from the wind-blown hillside 20 miles east of Cody, Wyo., looks like something from a Hollywood Western. Sixteen wild horses graze among the sagebrush, framed by a backdrop of parched buttes painted ochre and tan. Nearby, two figures in brown work pants and long-sleeved Western shirts squint into the distance. One has a rifle slung over the left shoulder.

The unarmed member of the duo, Patricia Hatle, turns to me and says, matter of factly, “Well, let’s see what we can do.” It’s time to go shoot horses.

A crisis can make for drastic measures. And the country’s effort to rein in the West’s wild horses is in crisis. Armed with dart guns loaded with a birth-control vaccine, horse lovers, scientists, and feds like Hatle, who works for the U.S. Bureau of Land Management, are trying to shoot their way out of the problem.


Folks far from the deserts of the mountain West might wonder why anyone is worried about wild horses. The animals have attained a mythic status as symbols of freedom and the Wild West, portrayed in everything from paintings to DreamWorks’ cartoon movie Spirit.*

a herd of horses in the desert east of Cody, Wyo.
Patricia Hatle (right) scans a herd of wild horses in the desert east of Cody, Wyo., as Ada Inbody waits to get close enough to dart one of the mares with a birth control vaccine.

Courtesy of Warren Cornwall

But a majestic icon can also be a four-legged pest. Today’s horses are an invasive species, introduced to the Americas by Europeans. Left unchecked, they overwhelm fragile desert ecosystems by chomping too much of the greenery to stubble. And they compete for the grass with another invader that has more economic clout: cattle.

For much of the 20th century, ranchers and the federal government dealt with wild horses by shooting them or hauling them to slaughterhouses. That all changed in 1971 when Congress passed a law saying the government should protect and manage the animals. Since then, the BLM has been stuck on a horse-powered hamster wheel. To keep the population in check, the agency periodically corners horses using helicopters and then ships them to permanent horse farms. Some get adopted. Many spend the rest of their lives there. The roundups anger horse advocates, who say they traumatize the animals. And it has a fatal flaw. As soon as the horses are carted off, the remaining ones start breeding again.

The situation has grown so grim that the status quo is impossible. The government has nearly 50,000 horses in captivity at a cost of $46 million a year, wild horse adoption rates are low, animal welfare groups are calling for fewer roundups, and ranchers are suing for more. “Our backs are against the wall,” said Tom Gorey, a BLM spokesman.

A decade ago, Hatle was caught in this familiar cycle. In 2004, the BLM rounded up 362 horses, leaving approximately 85 in the McCullough Peaks, 110,000 acres of arid foothills, mountains, and barren badlands east of Cody. The removal of much of the herd—a tourist attraction and source of local pride—concerned Cody horse fans. They formed a group, Friends of a Legacy, and started urging the BLM to find another way to handle the horses.

One leader of FOAL is Ada Inbody: Hatle’s rifle-toting partner who today works with Hatle and the BLM to control the horse population.

The technique they use was developed by Jay Kirkpatrick, an expert in reproductive physiology from Billings, Mont., who has become a pioneer in chemical contraceptives for wild animals. The nonprofit he founded, the Science and Conservation Center, manufactures porcine zona pellucida vaccine. It’s a vaccine made from pig ovaries that causes an immune reaction blocking an animal’s eggs from being fertilized. PZP has been tried on everything from African elephants to deer. Kirkpatrick has used the vaccine for 19 years to control horse populations on Assateague Island, a federal wildlife refuge off the coast of Maryland.