PICEANCE BASIN – The wild mare is wary, her tail arched and nostrils flared, as Cindy Day points a camouflage dart gun out the window of her Jeep Wrangler and peers through the scope. The reddish-brown horse is just 18 yards away.

Day is about to squeeze the trigger when a single-minded stallion sidles up to the mare and stands in the line of Day’s shot. And the mare, called BP2134, bolts.

Minutes later, Day heads out into the Piceance Wild Horse Management Area on foot, through the sagebrush and cheatgrass, an X-Caliber Projector the size and shape of a rifle slung over her shoulder. She accidentally sits on a cactus, getting pricked through her jeans, while crouching to look small so the band of horses with the mare that needs a fertility-control dart doesn’t spook again.

She sits quietly near a tree for more than 20 minutes.

From 35 yards, Day shoots a dart filled with fertility-control vaccine into the mare’s right hip. The startled horse spins, and either to get away from Day or the stallion that wants her attention, takes off running with the dart still stuck in her butt. It drops somewhere among the high-desert forbs, and Day and her sidekick Kathy Degonia, both volunteers with the Piceance Mustangs, spend the next half-hour unsuccessfully scouring the ground for the bright-orange dart.

In five hours in the Piceance, Day managed to dart just one mare. This is a typical day for her on the Western Colorado rangeland, about an hour outside Meeker.

Fertility control is an oft-touted solution for the wild horse and burro overpopulation problem, which for decades has pitted mustang advocates against federal regulators at the Bureau of Land Management who have rounded up 1,500 wild horses in Colorado since 2021. The horses end up in holding pens, including on state prison grounds in Cañon City, where 145 mustangs died last summer from the typically preventable equine flu.

Day, Degonia and the rest of the 50 or so Piceance Mustangs volunteers represent the middle ground – they are horse lovers and, at the same time, partners of the BLM. Their group, along with similar groups at the three other herd management areas in western Colorado, does the work needed to keep horses alive during drought years and, in general, makes horse management easier on the BLM. The volunteers have hauled water; converted windmills to solar power; placed water troughs; removed old fences that trip and injure the horses; and assisted in roundups by telling the BLM which horses they want released back to the land for genetic diversity.

They are often, too, the target of criticism from national and local mustang advocacy groups that are fiercely opposed to helicopter roundups and question the safety of fertility-control vaccines. One advocate shouted “baby killer!” at Day after attacking her about fertility darts during a wild horse adoption event the Piceance Mustangs held in Craig last month.

The vaccine, called GonaCon, interrupts ovulation and can prevent mares from getting pregnant for up to four years.

Unlike the mustang advocacy groups, which challenge the BLM’s assessment of how many horses the land can handle, the Piceance Mustangs support a plan to get the herd to the BLM’s “appropriate management level” and then maintain that level with fertility control.

But darting wild horses is painstaking, requires more patience than the average person has the capacity to handle, and, if it weren’t for the fact that Day and other horse lovers volunteer their time, might require more taxpayer money to accomplish than some people are willing to spend.

Since the fertility program began two years ago, Day and mainly one other volunteer have landed darts in about 140 mares in the Piceance Basin. About 55 others were treated with the vaccine and released after a federal roundup.

And, according to a handful of studies, the darts work about 55% to 70% of the time, and that’s after an initial dose and a booster shot. Day recently saw a stallion “covering,” or mounting, a mare that had been treated with two doses of the vaccine, which might mean the vaccine didn’t work.

Darting is far less efficient at maintaining population control than a BLM helicopter roundup, which can corral hundreds of mustangs within a few days. The Piceance-East Douglas wild horse range has an estimated 750 horses, though it’s hard to count them accurately in the rugged terrain rimmed with red-dirt bluffs and pockets where no roads go. And that’s after 761 were rounded up last summer, most of them by a low-flying helicopter, and hauled to a BLM holding facility in Utah.

The public land, nearly 200,000 acres dotted with piñon and juniper trees, can handle 235 horses at maximum, according to the BLM. Wild horses are roaming in an area closer to 500,000 acres, however, including on surrounding private land.

“We have so many horses,” Day said, pointing in the distance toward a flat-topped mountain pocked with jagged cliffs and crevasses. “When you stop and think that a lot of the land looks just like that mountain there in front of us, yeah, we really truly have no idea how many horses we have.”

During last summer’s roundup, the helicopter drove in bands of horses that Day and Degonia, who is president of the Piceance Mustangs, had never seen before.

The federal agency’s goal is to remove an additional 500 or so horses from the Piceance, then attempt to continue to dart the mares with birth control, one $50 dose at a time. The bureau has one roundup planned for 2023, a removal of about 70 horses from the Little Book Cliffs herd management area near Palisade in September, but no roundup planned in the Piceance this summer.

“The fertility control helps us have fewer gathers,” said Brittany Sprout, spokesperson for the BLM in Colorado. “The goal is to eventually get to the point where we don’t have to have gathers and we can rely on fertility control.”

But the agency has no plans at this point to invest in a paid team of fertility darters and will instead continue to rely on volunteers, Sprout said. “We have a very passionate community in Colorado and we have a lot of groups that love wild horses.”

For now, the task falls to Day, who quit her career as a real estate agent to spend her days bouncing over roads in the Piceance looking for horses she knows by name, or at least by number. She makes the two-hour trek from Grand Junction a few times a week, and when she can, she camps in the basin for days at a time.

Heading out on hot and breezy June morning, Day went through her supply checklist:

Dart gun. Carbon dioxide canister to propel the darts. Binoculars. Rangefinder to measure the distance between horses and her dart gun. iPad loaded with the wild horse database, so she can keep track of which mares need the vaccine.

Syringes. 15 darts. And three doses of fertility-control vaccine, stored in a Yeti cup with a plastic baggie filled with ice.

Day and Degonia, both wearing jeans, boots and their Piceance Mustang T-shirts, have also packed lunch, because they never know how long a day in the basin will last. As they drive into the Piceance, between the towns of Rifle and Meeker, they chat about horses they hope to find.

Buttermilk Biscuit is at the top of Degonia’s list because she wants to know if the palomino stallion fathered a new spring foal. But first, the women head toward a dirt road hugging Yellow Creek, looking for a sorrel stallion called Tucker whose band includes a few mares that have yet to receive fertility-control darts.

Within minutes, they spot Tucker leading a colorful band of roan and bay mares and spring foals. The horses are on the move though, and followed by a six-member bachelor band, a group of stallions that hang together because they haven’t yet managed to win their own mares. “Oh, that’s Blue Spice and Nutmeg,” Day says, recognizing some of the bachelors that are mostly named after spices.

They are moving too fast for Day and Degonia to get a dart ready, racing away from the road and over a hill covered in sagebrush taller than people.

The Piceance is lush this year, surreal after years of drought when the Piceance Mustang volunteers hauled in tanks of water so the horses wouldn’t die of thirst. In some of the worst years, including 2021 and 2022, Degonia pulled up to an empty water trough with a water tank in the back of the truck and “60 thirsty horses staring at her.”

This summer, though, the creeks are rushing and the grasses are tall. Red Indian paintbrush and purple lupine flowers bend in the breeze. The cactuses bloomed in June, punctuating the rolling hills with pops of pink and yellow.

“This is the best year for water we’ve seen in a long, long, long time,” Degonia said. “And the grass out there is unbelievable this year. Never seen grass like there is out there right now.”

She knows better than most, though, how quickly the rangeland can turn to dust once it stops raining.

The federal land is also used by cattle, which have taken over some of the grassy meadows where mustangs once spent their summers. Oil and gas companies lease the land, too, and oil pads often share the same patch of dirt with water tanks for the horses. In one spot, a hunting blind where volunteers can watch for mustangs and shoot them with darts sits next to a horse water trough and an oil pad.

Day and Degonia praise the oil and gas crews for creating and maintaining roads in the basin that make it easier for them to find horses. They wave when they pass a field worker in a pickup truck, and Day mentions that they’ve all gotten used to her driving. She’s been known to hit the brakes hard when she spots a horse from a mile away.

The women exchange seats in the Jeep throughout the day, depending on which side is closest to the horses. Degonia is the spotter, armed with a camera and binoculars.

Whenever they see horses, they stop about a half-mile away, then try to identify them with their binoculars. They look for identifying marks, like white stockings or slashes on their noses. Many of the horses in the basin are what they call NDF – no defining features. They’re bays, brown with black mane and tail and no white.

“If you have no identifying marks or anything, that’s a shot in the dark,” Day said.

But if she can identify them, she opens up her iPad to find out whether they’ve had a dart and when. Then she prepares her gun, using a syringe to inject the fertility-control vaccine into a dart. Degonia, the spotter, raises her camera with a telephoto lens. Her goal is to take photos that will help identify and name every horse in the band, of the dart landing in the horse’s butt, and of the dart falling to the ground, so they can find it when the excitement is over.

The women creep closer, one driving and one using a rangefinder to gauge the distance for the shot. “The furthest you can dart is from 55 or 50 yards,” Day said. “That’s pushing it. I don’t like to dart that far. My optimum is about 30 to 35 yards because that’s the breaking point where the sound of the dart arrives at the horse before the dart.”

If there’s wind, she needs to get even closer. “The darts are so light and there are so many variables,” she said. “If there are six other horses there, you could get it in an eye and that’s not worth it to me.”

Or you could accidentally shoot a stallion or a foal.

Volunteers in the Piceance have accidentally darted a couple of stallions, Day said. The male horses have no sex drive for at least the next year, and temporarily lose their mares and end up living alone, she said. This is part of the reason some mustang advocacy groups are opposed to her work. Some are also concerned that some stallions or mares dosed with the vaccine might end up sterile forever.

“We don’t want to play God necessarily,” Day said. “But we would like to be able to have more say in how many foals we have born every year. And you don’t want them sterile forever because then you don’t have the diversity and genetic diversity.”

The BLM supplies the dart gun, rangefinder and other supplies that Day takes into the basin, and will pay her 14 cents per mile if she turns in her mileage reports. The agency also pays for the GonaCon. Clearly, Day isn’t doing it for the money. “It’s my heart,” she said.

The BLM treated 349 mares with fertility-control vaccines last year in Colorado, many of them after they were gathered during roundups and released back to the wild.

The three other horse management areas in Colorado – Sand Wash Basin in the far northwestern corner of the state, Little Book Cliffs near Palisade and Spring Creek Basin in Disappointment Valley in the southwest – don’t use GonaCon, but the more traditional vaccine called PZP. While GonaCon can prevent pregnancy for up to four years after two doses, PZP requires an annual booster to stay effective.

The Colorado Legislature passed a law this year that attempts to give the state greater authority of wild horse management. The measure, signed by Gov. Jared Polis in May at Little Book Cliffs, comes after conflict in the past two years between the governor’s office and the BLM after a helicopter roundup of Sand Wash Basin horses in 2021.

The BLM ignored the governor’s pleas to halt that roundup to consider a “more humane” option other than a helicopter. The new law calls for spending $200,000 next year to create a working group that will make recommendations to the governor’s office about nonlethal, long-term solutions to control the mustang population, including a state fertility-control program and possibly a wild horse sanctuary.

And after the federal government removed more than 30,000 horses in 2021 and 2022 from rangeland across the West, Congress is considering a new law that would prohibit helicopter roundups and require the BLM to spend millions of dollars on fertility control next year.

Day, who grew up on a horse ranch in Eagle County and packs a 9 mm handgun when she’s in the basin alone, looks forward to a time when the basin no longer is under threat of helicopter roundups, when the number of horses in the Piceance is within the BLM’s 235 limit.

Hired staff couldn’t step in and do her job without first getting to know the mustangs, she said.

At the end of a long day, with only one mare darted even as she was chased by a randy stallion, Day and Degonia spot a band of horses up on a hillside making their way toward water. They’re no longer in the herd management area, but on private ranch land sprinkled with yellow clover.

The scene is like a postcard, and Degonia gasps when she sees the palomino stallion she’s talked about all day. It’s Buttermilk Biscuit, leading his brood toward a rushing stream. A little gray foal trots along behind.

Degonia stands up in her seat and raises her camera out the sunroof. Then she’s out of the Jeep, scrambling to get a closer view of the stallion.

He’s 100 yards away, cautious as he sips from the stream. Then his head jerks up, ears perked. He steers his band away from the water and the road, up the hill and out of sight.

The Colorado Sun is a reader-supported, nonpartisan news organization dedicated to covering Colorado issues. To learn more, go to coloradosun.com.