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Thinning the Herd

The Bison of Catalina Island showcase responsible wildlife stewardship

On a perfectly balmy day in the rugged hills of Catalina Island, about an hour off the coast of California, biologist Julie King peers through the crosshairs of a mounted telescope at a pooping bison.

She records the time the droppings hit the ground, the identification tag of the half-ton offender, and which telescope was used to mark the pile’s location. A few minutes later, calling out instructions over the steady hum of planes flying overhead toward island's private airport, she guides fellow biologist Calvin Duncan down to exact location of the dung.

“No, keep going back!” King yells out as he treks through shrubs to locate and retrieve samples of the fecal matter. Success is swift. “Bingo! That’s it!”

Behind this unglamorous ritual, repeated two to three times a week, lies an oft-hidden practice making waves in the world of wildlife care: putting animals on birth control.

Across the world, out-of-control wildlife populations and invasive species are severely impacting the ecosystems they occupy. These creatures destroy the local environment and drain natural resources, making life difficult for vulnerable endangered animals and causing billions of dollars in damages. There are feral pigs in Texas, grey squirrels in England, foxes and water buffalo in Australia, and iguanas in Florida. In Chile, invasive red deer have put severe pressure on south Andean deer, an endangered species. And before the yellow-legged hornet caused devastation in beehives across France, a Siberian chipmunk invasion wreaked havoc in Paris.

Biologist Calvin Duncan gathers samples of bison poop

On Catalina Island, though, they had a bison problem. Faced with an expanding herd that was increasingly becoming unsustainable for the 21-mile-long island’s delicate ecosystem, the Catalina Island Conservancy, a nonprofit charged with looking after most of the land, initiated a program to put its free-roaming beasts on contraception.

Four years later, the program has successfully reduced the teeming herd to a manageable number of just under 150 animals. Now in the second phase of their research, Duncan and King are tracking breeding behavior and hormone levels in fecal matter for a greater purpose—to see if this alternative approach has broader potential.

King and Duncan’s hope is that their success with bison can be replicated by others trying to maintain the balance between flora and fauna in increasingly fragile environments. While approaches to dealing with the problem vary by species and location, worldwide controversy surrounding the question of how to manage free-ranging animals is at an all-time high.

“I think we’re moving further and further away from being able to use lethal control,” Duncan tells me.

In the age of the internet and social media, fierce societal opposition to lethal culls—especially of America’s most iconic animals, like bison and horses—has become apparent. Yearly culls of bison at Yellowstone National Park, for example, draw angry opposition every year, where hundreds of thousands of activists demand a stop to the slaughter and have even attempted to physically blockade the operation.

Biologist Julie King scopes out the herd

Could wildlife birth control potentially be a viable solution?

For now, these progressive management methods are working wonders for a California bison herd with Hollywood roots, left behind on Catalina Island and the cutting room floor.

In December 1924, the Famous Players-Lasky Corporation, known today as Paramount Pictures, shipped and freed 14 American bison on Catalina Island with the intention to use them for background in a silent Western film. The details of exactly what film they were meant for remains murky, but the bison never appeared in any of the studio’s movies. With nearly a million people visiting Catalina each year, the island economy depends largely on tourism, and the bison became a major attraction for West Coast visitors. But over the next four decades, the bison population ballooned to about 600 animals—too many for the island to sustain. After several years of research, scientists determined that a herd of around 150 would be ideal.

[quote position="full" is_quote="true"]Worldwide controversy surrounding the question of how to manage free-ranging animals is at an all-time high.[/quote]

The innovative tool they would use to accomplish herd reduction was a contraceptive agent made from pig ovaries known as porcine zona pellucida, or PZP. PZP was a failed human contraceptive discovered in the 1970s by Alex Shivers, then a zoology professor at the University of Tennessee. Though it turned out to be marginally effective for people, it just wasn’t effective enough—PZP fell short of the dependability and accuracy required to put a contraceptive drug on the market, and a synthetic form was never successfully developed.

Rather than effecting hormonal changes, like human contraceptives whose active ingredients are synthetic versions of female hormones, PZP causes female bison to produce antibodies that prevent sperm from attaching to eggs and fertilizing them. This form of birth control is referred to as immunocontraception; by using a kind of vaccine, the method causes the body’s own immune response to prevent pregnancy. Unlike other immunocontraception methods, PZP does not affect hormone levels, which means it doesn’t result in changes in behavior.

In the fall and winter of 2009, female bison—called cows—were rounded up on Catalina Island, temporarily restrained in a squeeze chute, and treated with PZP by hand. At the end of 2013, the Catalina Island Conservancy released the results of Duncan and King’s efforts: They had effectively reduced the calf birth rate of the island’s bison population from 67 percent to 10 percent in the first year. The following year it dropped even further, to just 3 percent and then to 1.6 percent; in 2014 no calves were born at all. The pair had successfully, for the first time, curbed a wild bison population without culling or causing distress to the animals.

Duncan carefully prepares a dart of PZP

PZP is made at the Science and Conservation Center in Billings, Montana, by reproductive biologist Jay Kirkpatrick and his small team, which generates about 3,500 doses of PZP annually. The process of manufacturing the drug is laborious and time consuming. It must be done by hand, making the current supply limited and therefore relatively precious. Kirkpatrick, who is in his 70s, is a straightforward educator with a biting wit who rides a moped to work. He grew up surrounded by nature in rural Pennsylvania, where he had a pet crow and dozens of snakes. In a former life, he was a park ranger. But now, animal fertility experts, scientists, and researchers know him as “the godfather of wildlife birth control”—though it’s not a title he particularly likes. “Why don’t we just say that I was there in the beginning,” he says.

For decades, Kirkpatrick has been the world’s most vocal and successful pioneer in the realm of animal contraception. His foray into the field began over 40 years ago, when two cowboys knocked on his door at Montana State University in Billings where he was an assistant professor of physiology. They introduced themselves and asked a question that took him by surprise: “Can you make horses stop reproducing?”

It was 1971, and President Nixon had just passed the Wild Free-Roaming Horses and Burros Act, giving legal protection to thousands of wild horses living on public land. Because the act made it illegal to cull the horses, a new more humane method needed to be implemented to keep numbers at bay.

Photo by Jaime Jackson via Flickr

“It was well intentioned legislation, but it had no element of management in it,” Kirkpatrick says.

Managing rising wild horse populations in the U.S. became a disaster. Because the horses have no predators and are particularly fecund animals, their herd sizes can double every four years. Their numbers rose from an estimated 17,000 to a peak of between 65,000 and 80,000 in the decade following the act, according to the Bureau of Land Management, the agency in charge of managing wild horses and burros. Over time, this has led to a situation in which wild horses cost American taxpayers $77 million every year—a majority of which is spent caring for the animals—and the question of how to deal with these populations has become a wrought, controversial issue.

Horse advocates accuse the BLM of catering to ranchers, who they say scapegoat the horses because they have to share public grazing lands with them, even while paying low fees for their cattle and sheep to use the land. The horses are also often subject to what advocates say are cruel roundups, where the roughly 50,000 animals that the BLM feeds in short- and long-term corrals and pastures are herded by hovering helicopters, terrifying the animals—some of which die in the stampede.

And while animal birth control might seem like the most obvious, humane fix, Kirkpatrick has faced his fair share of criticism, too—animal rights groups accuse him of violating the reproductive rights of animals and trying to sterilize them. They want the horses left alone and managed holistically, but Kirkpatrick says that that’s not a viable solution.

“You can’t do that. They’re not free-roaming, they’re fenced; they can’t migrate 300 to 400 miles if there’s drought,” he says. “That’s akin to putting a bunch of dogs in a big kennel, putting some food and water, and walking away.”

He’s also faced cultural pushback from those who prefer roundups and ropes.

“Whether they work or not, there is a culture in the West of course that looks at fertility control [methods] in wildlife as bizarre and crazy.”

Jay Kirkpatrick. Photo courtesy of

Kirkpatrick has spent much of his time trying to persuade the federal government to implement wildlife contraception as a humane means of control without any wide-scale luck. Last year, however, the BLM administered PZP and PZP-22 (a longer-lasting version of the contraceptive) to 384 mares, and announced a plan to award 10 grants of up to $1 million each to create sterilization and contraception programs.

Despite slow traction with authorities and pushback from animal advocates, Kirkpatrick has made significant headway in other areas. The Science and Conservation Center now supplies PZP to tribal lands and sanctuaries in the U.S. as well to Hungary and Canada. In Romania, a contraception project was initiated last year to preserve 500 wild horses living in the Letea Forest, situated in the northeast part of the Danube Delta. It treats elephants in 20 different game parks in South Africa and sends out the vaccine to over 200 zoos in more than 10 countries. All over the world, wildlife birth control is cautiously being seen as a management alternative for overpopulated animals that would otherwise be killed.

Kirkpatrick calls the bison birth control project at Catalina a “model program.” He praises the “huge implications” of Duncan and King’s pioneering efforts, which have caught the attention of places like Yellowstone National Park, where 900 bison were culled this past winter.

“They’re doing everything right,” Kirkpatrick says. “The whole goal will be to finally settle into a routine where birth rates equal mortality rates and the herd stays at the same size.”

Back in the field on Catalina, Duncan readies an air-powered rifle, preparing to dart a few cows with their annual dose of PZP. The orange dart, which he’s painted for better visibility once it falls on the ground, will hit the rump of a cow, administer the vaccine, and bounce out.

“Number 54 is in a good position right now,” Duncan says.

Duncan shoots 54, a quick delivery that startles the bison for a few seconds before they focus their attention back on grazing.

“I think we’re demonstrating that the application … can be done in wild populations, and I think it’s going to expand,” he says.

[quote position="full" is_quote="true"]There is a culture in the West of course that looks at fertility control [methods] in wildlife as bizarre and crazy.[/quote]

Expansion does indeed appear a likely outcome as the potential of this method, unorthodox as it might initially seem, catches on with those charged with maintaining delicate ecosystems everywhere. The experiment with the island’s bison is a proof-of-concept, an isolated testing ground for what could one day be a solution to not only America’s problems with wild horses, but for rampaging animal populations anywhere on Earth, and the environmental and economic price tag that comes with them.

The dire plight of these animals fighting for resources is a consequence of human behavior, and killing these creatures to control population size is commonly seen as an unsustainable, if not inhumane, option. Since we have displaced them, shrunk or eradicated their ecosystems, and otherwise manipulated their fates, we must now imagine new kinds of stewardship that include a new set of tools, like contraception. But the situation remains complicated. Bureaucracy and politics are messy, and culture is a hard thing to change—even with a herd of hairy, half-ton bison staring you in the face.

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