Reining in a Runaway Herd
With a little help from mountain lions, researchers in Nevada are learning to bring wild horse populations under control
- Michael Tennesen
- Oct 01, 1992
First light spreads its long shadows from the boulders and cacti that dot the high mountainous desert where Nevada meets Central California. John Turner, a bearded, wiry, soft-spoken biologist, steps out the door of his mobile field station at the edge of the Montgomery Pass Wild Horse Territory and stops to watch a band of about a dozen wild horses grazing nearby.
It's the start of a big day for Turner. In a few minutes, scientists and officials from the U.S. Forest Service, Bureau of Land Management (BLM), the Nevada Department of Wildlife and the Commission for Preservation of Wild Horses will be joining him for his annual wild horse census.
By nightfall, the team will have reconfirmed a finding Turner made several years ago about the Montgomery Pass herd: While populations of other western wild horse herds are mushrooming, predators operating in a natural system of checks and balances keep these animals' numbers under control.
In 1971, the Wild Free-Roaming Horse and Burro Act made it illegal for anyone to harass, capture or kill wild horses. Since then, populations of the animals have soared throughout the Great Basin Desert, which lies mostly in Nevada and extends to the fringes of surrounding states. A Congressional amendment to the act in 1978 allowed the removal of animals for adoption. But so far, adoption has proved an expensive and ineffective way to rein in the horses' growing numbers.
"Wild horse herds have been expanding 10 to 20 percent each year," says Turner, an endocrinologist at the Medical College of Ohio. "At that rate, populations can double every five to ten years." The result: too many horses and too little room. Last summer, about 2,000 wild horses were removed from Nevada's Nellis Air Force Base because of severe overcrowding.
Turner and Utah State University researcher Michael Wolfe insist that populations of wild horses at Montgomery Pass do not follow the typical pattern. The scientists have been studying the herd for seven years, or ever since they met at a conference where Turner was speaking about the potential of birth control for horses. At the time, Wolfe was looking into the population dynamics of wild horse herds, so they decided to work together.
Turner and Wolfe now believe the Montgomery Pass herd has been checked by growing populations of mountain lions. Until recently, says Wolfe, "mountain lion kills have been recorded only incidentally, never stabilizing an entire herd." If their findings bear out over time, they could have implications for horse management throughout the creatures' range.
But if nature alone can't do the job, maybe people can help. To that end, Turner is working with a team of other researchers on a different approach to controlling horse populations: contraception. The scientists have successfully tested a new birth-control drug on wild horses in Maryland and California.
That help in capping the wild-horse population explosion may be on the way is welcome news to ranchers and horse lovers alike. In an unlikely alliance, Nevada biologists, protectionists, government officials and ranchers have shelved their differences--at least for now--and come up with a plan that may lead, finally, to successful management of wild horse herds.
The horse made two distinct appearances on the North American continent during the course of its history. The first was about 55 million years ago, when the animal's ancestors arrived from Asia via the Bering land bridge. This early creature bore only a slight resemblance to the modern-day horse. "If you were to lay out its skeleton, bone for bone, it would be no bigger than a house cat," explains Phillip Gingerich, a paleontologist at the University of Michigan. "And it walked on its toes like a house cat."
Over the millennia, the animal slowly grew to a size close to that of today's horse. It lived as part of a balanced ecosystem along with dozens of other herbivores--the giant ground sloth, giant beaver, camel, mammoth and mastodon, among others--and such predators as the dire wolf and saber-toothed cat. That all changed rather abruptly about 10,000 years ago, when humans crossed over the same land bridge. Soon the horse and the other large animals disappeared, victims, some scientists say, of prehistoric overkill.
North America remained horseless until about 500 years ago, when explorers from Spain introduced more of the animals. Some of the horses that broke away from expeditions in what is now the southwestern United States made their way to the Great Basin as early as the 1600s.
When these feral horses entered the North American ecosystem, they may have stepped into an ecological vacuum left by their primitive forebears, a vacuum that early European settlers helped secure by wiping out grizzlies and wolves. Today, Montgomery Pass is the only known area in the horses' range where predators keep herd populations in check. On the California side, mountain lions are protected by law; on the Nevada side, the cats receive only limited hunting pressure.
Ten western states currently host wild horses. According to Bureau of Land Management estimates, the total U.S. population in 1990 was about 42,000, with some 34,000 of them in Nevada. Feral horses also live in parts of Canada, France, England, Siberia and New Zealand. Australia has the most, with more than 600,000. All of these animals are descended from former domestic stock. (Przewalski's horse, which once roamed the Asian Steppe, is the only truly native species remaining, but all 400 or 500 of them now live in zoos.)
Horses in the Great Basin weigh anywhere from 800 to 1,300 pounds. Their color range spans the equine rainbow, though wild horses are seldom as pretty as their tamer counterparts. "Domestic animals are bred for looks and performance," explains Irwin Liu, a professor of veterinary medicine at the University of California at Davis. "Nature breeds wild horses for reproductive efficiency."
During winter, wild horses at Montgomery Pass roam in bands containing one stallion and several mares and their young. Come summer, these bands congregate at higher elevations in groups of as many as 70 animals--perhaps in response to mountain lion predation.
Most Montgomery Pass females come into heat between May and July, shortly after giving birth to the season's foals. This is the time when hostility among males reaches the boiling point. Harem stallions aggressively defend their mares from equally determined bachelors. Sometimes free-lance males work as a team: While one harasses the harem stallion, the other steals a mare away from the group. These incursions can lead to serious fights, with competing stallions rearing up and "boxing" with their powerful forelegs.
While studying a herd of wild horses at Nevada's Granite Range, Joel Berger, a biologist with the University of Nevada in Reno, determined that fully 95 percent of the adult males bore wounds or scars from bouts with other males. Three percent died as a result of fighting.
John Turner began studying wild horses at Montgomery Pass in 1985, when the U.S. Forest Service proposed reducing the herd from 190 animals to 75. Before long, he became puzzled by the relatively high level of foal mortality. While 90 percent of the foals in other parts of the Great Basin survived to become yearlings, only 25 to 40 percent at Montgomery Pass made it to their first birthday. An investigation suggested the cause: "The range wasn't overpopulated," Turner says. "Mountain lions had it under control."
Turner and Wolfe have evidence indicating that at least five mountain lions prey on the Montgomery Pass herd. But it's hard to be certain with creatures as elusive as these wary cats. After 5,000 hours of field observations, only once did anyone in Turner's group actually see a mountain lion take a foal. When the predator attacked, according to the witness, other horses in the vicinity bolted, fanning out in different directions. Watching anxiously from a distance, the animals made no effort to protect the foal.
Hoofprints Turner has examined from a number of similar kills suggest the same pattern: Unlike deer, bison and pronghorn, which try to protect their young, horses simply flee. "Running away is what evolution has given the horse to deal with predators," explains the scientist, "and it has been quite successful for them."
Once they've learned to run, most horses can outpace a mountain lion. Until then, though, they are easy targets. The majority of foals that end up as cat prey are taken in late spring and summer, when the horses are just a few months old. These kills alone are enough to keep the Montgomery Pass wild horse population relatively stable. Still, neither Turner nor Wolfe views mountain lion predation as a cure-all for horse overpopulation. As Wolfe observes, "Livestock interests in Nevada wouldn't be too keen on large transplants of mountain lions."
Perhaps a more promising technique is fertility control. Turner is working with Irwin Liu and Montana researcher Jay Kirkpatrick on a contraceptive vaccine that causes a female horse's body to reject its own eggs. The BLM plans to test a version of the drug this fall.
For now, though, adoption remains the only legal way to handle excess horses. Under a program administered by the BLM, some 5,000 to 6,000 horses are removed from the wild each year and given to qualified owners. Unfortunately, the project has been plagued by problems and a huge price tag. BLM currently holds more than 3,300 older, less adoptable, animals at sanctuaries in South Dakota and Oklahoma at an annual cost to taxpayers of $1.8 million. The yearly cost for the entire program is $13.5 million.
Since the passage of the Wild Free-Roaming Horse and Burro Act two decades ago, the history of horse management has read like a prize fight between ranchers and horse protection groups, with the BLM trying to referee. Preservationists accuse ranchers of shooting the animals, while ranchers blame wild horses for fouling water, competing with domestic livestock and displacing native species such as pronghorns and bighorn sheep.
Recently the BLM, along with a number of local, state and national advisory boards, came up with a five-point plan that just may spell compromise. First, the plan acknowledges the wild horse as a valid part of the Great Basin ecosystem, not just a pest. It also provides for studies to determine the number of horses, livestock and wildlife each range can sustain.
The group agreed that only one- to four year-old horses should be removed for adoption, as those are most likely to find a home. Planners also expressed a commitment to fertility control as the way of the future for wild horse management.
At the BLM state office in Reno, the proposal was presented to representatives from all groups concerned. "Everyone liked it," says Cathy Barcomb, executive director of the Commission for the Preservation of Wild Horses in Nevada. "I was so excited, I felt like sending up flares."
"This is the first thing that has come from BLM on wild horse management that has ever made any sense," echoes Jim Connelley, president of the Nevada Cattlemen's Association. "I hope they are successful beyond their wildest dreams."
California writer Michael Tennesen traveled to Montgomery Pass earlier this year for the annual wild horse census.