year after that. The agency didn’t see this as practical. It also wanted proof the contraceptive would work out West, on larger herds that might not be approachable, and on land that was millions of acres, not a small island. PZP-22 promised to address the first concern because it was a longer-acting version of the drug—boosters suspended in the initial vaccine in time-release capsules are delivered after one, three and 12 months. To address the second concern, The HSUS used a $1.7 million grant from the Annenberg Foundation to try out PZP-22 at Cedar Mountains and Sand Wash Basin starting in 2008. The trials are aiming to replicate results of a 2007 study in the BLM’s Clan Alpine, Nevada, management area that found that PZP-22 lowered the foaling rate of individual wild horses to 5 percent the first year after it was administered and 15 percent the second year (untreated horses in that area had foaling rates of 54 percent and 59 percent during those years).
If PZP-22 can keep annual population growth to 10 percent—which Rutberg, the professor and PZP researcher, believes it can—the contraceptive will be worthwhile to use at Sand Wash, Fox says. He’d only have to dart every two to three years and he could stop large roundups, selectively gathering only younger animals likely to be adopted. At Cedars, Warr says that even if the results are not quite that good, he would propose removing 200 horses and then, with the herd down to 400, try to treat all the mares.
Except when they’re thirsty, the Cedars horses aren’t easy to reach. Finding the herd requires long hikes or horseback rides. Kayla Grams, HSUS head field technician, says she spends a lot of her time sneaking up on horses, but the closest she’s ever been able to get to these animals, who’ve been shot at, is 50 yards. The horses can hear well and are alert to smells and to alarm signals given by other wildlife, like pronghorns, and by each other. “It’s sort of like hunting. I usually want to be downwind. I use vegetation to hide. I’ll sneak down a gully; I’ll crouch really low; sometimes I crawl on the ground.”
So darting at Cedars is impossible. Administering PZP-22 there requires rounding up the horses and hand-injecting the drug. Helicopter gathers in 2008 and 2012 allowed Grams to treat 75 percent of the mares.
Sand Wash Basin is a much easier place to contracept horses. To reach the herd all you need to do is drive up along a road, park your truck and take a hike. This means many local horse lovers know the herd and tourists visit, so the animals are used to people. Even with wide open vistas and little opportunity to hide as she stalks the herd, Grams says she can get within 10 yards.
On a typical day at Sand Wash, Grams finds the horses in a band grazing, heads down. Once in a while, one looks up. The lead mare and the stallion are watching. Gradually, if a human approaches, the herd, taking a few steps here, a few there, will move off. So Grams walks nonchalantly toward the band, acting as though she really isn’t headed that way at all. She passes them and waits with no movement, like she is a tree rather than a person. Patiently, she sticks with the band, dogging the group of horses the way “bachelor” stallions do when they are hoping to steal a mare from a stallion’s harem. Sometimes, she hides behind brush or rocks. After a long time, she can get within 40 or 50 yards, close enough to take a shot—but only if the wind isn’t blowing.
Grams targets subordinate mares first, waiting to dart the lead mare last because that horse will alert the others. As the horse she’s targeting moves within range, she creeps closer, stops, then creeps closer again, while the horses in turn adjust their positions, ambling always a little farther out of reach. Finally, she takes her shot. The dart hits the mare in the hindquarters, delivering the vaccine. The mare’s only reaction is to kick up her legs. But all at once, the other horses move subtly, putting their bodies between Grams and the lead mare or another horse she is targeting. Usually, she does not get another clear sh