Wildlife Contraception

By Douglas Fox

A lone elephant hurries toward a stand of trees as the whoop-whoop of a helicopter looms overhead. The helicopter swings within a few yards of the elephant, and she breaks into a run—but not soon enough. A rifle shot rings out, and a splash of red erupts onto her thigh. She’s been hit. But she doesn’t stumble and fall. Instead, she continues running because those rifle shots aren’t bullets: they’re darts containing purified pig proteins plus a bit of dye to mark the hit. The goal here at Makalali Reserve in South Africa isn’t to kill these animals but rather to contracept them: to trick their immune systems into preventing pregnancy in order to control populations. It’s the newest approach to a quintessentially modern problem—too many elephants roaming South Africa’s wild reserves, stripping leaves from trees and in some spots mowing the grass until it resembles a putting green. And it isn’t just elephants; on other continents, too many mallards, horses, deer, and kangaroos in the wrong places pose similar problems.

Wildlife contraception may sound a bit loony: an over-aggressive way of meddling with nature. That stigma is nothing new. The search for effective wildlife contraception has been a lonely slog, borne over four decades by a handful of believers who at times managed to attract the scorn of animal hunters and animal lovers alike.

But wildlife contraception has survived and may yet flourish. From game parks in South Africa to suburbs in America, people are desperate for this kind of tool. Authorities in South Africa managed elephant populations in Kruger National Park by culling up to 400 animals per year. After public outcry halted culling in 1996, park managers shifted to capturing elephants and moving them to other reserves. Within seven years, they saturated the market for surplus pachyderms, and the business of moving them ground to a halt, says South African big-game specialist J.J. van Altena, who moved many of the elephants himself. In a turn of fate, van Altena and others who once captured or culled elephants now administer family planning to them instead.

Like it or not, the fundamental goal is to downsize natural ecology to fit the geography of modern niches without altering the behavior of animals or the balance between species. It’s no simple task, but researchers are getting closer. In a world where pristine ecosystems are sacrosanct and the interfering touch is frowned upon, the search is on for an immaculate contraception.

And the demand will only grow, as suburban sprawl fragments landscapes, uncouples wild populations from their natural controls, and creates conflict between humans and animals. The 6th International Conference on Fertility Control for Wildlife in September 2007 in York, U.K., highlighted advances in the field and a wide range of experiments underway: hormonal implants, immune vaccines, cholesterol drugs recycled from flunked human studies, and even viruses or worms genetically engineered to stop reproduction.

Wildlife contraception began at least 1,000 years ago. Bedouins in North Africa are said to have inserted stones into the uteri of camels (possibly the world’s first IUD) to prevent them from becoming pregnant during long desert treks.

But the modern history of wildlife contraception begins in the fall of 1971. Jay Kirkpatrick, a reproductive biologist transplanted from Cornell University, was settling into his new position at Montana State University in Billings, where he planned to culture animal embryos. One Thursday afternoon a cowboy, hat on head and dust on boots, walked into Kirkpatrick’s office and asked him whether he could find a way to prevent wild mares from getting pregnant.

That man was Ron Hall, a wildlife biologist at the Billings office of the Bureau of Land Management (BLM). You might call Hall a visionary.

Wild horses weren’t multiplying out of control; yearly culls had kept their numbers in check across the Western U.S. But Hall understood that this crudely enforced equilibrium was about to explode. Congress had just passed the Wild Free-Roaming Horse and Burro Act, which outlawed killing of horses. If culling weren’t replaced with some gentler form of population control, horse numbers would double within a few years, endangering commercial rangelands across the West.

Kirkpatrick was intrigued, and he and his students began studying the horses’ reproductive biology at the nearby Pryor Mountains Wild Horse Range.

Back on campus, Kirkpatrick tried injecting captive stallions with steroids. It deflated their sperm counts and prevented them from siring foals, but—unfortunately—it involved injecting large amounts of liquid into the horses by hand, which in turn evoked the risky prospect of having to capture wild stallions one by one.

These technical challenges were soon dwarfed by problems of a different sort. Local residents accidentally learned of Kirkpatrick’s work in the Pryor Mountains when they overheard a conversation between two of his students at the Medicine Wheel tavern in Lovell, Wyoming—just across the state line from the Pryors. Kirkpatrick hadn’t even begun testing contraception in the Pryor Mountains herd, but rumors of his scientific machinations quickly spread. An editorial in the Lovell Chronicle cast contraception as a threat to wild horses and local tourism. “Go sterilize yourself,” said a personal letter mailed to Kirkpatrick.

The fracas reached Wyoming’s congressional delegation, which pressured BLM. Kirkpatrick was expelled from the Pryors within two months. He quickly understood that public opinion was the single strongest force that would sculpt his work. That force would buffet him again and again.

It wasn’t until a decade later that circumstance finally handed Kirkpatrick his big break. Despite BLM’s attempts to regulate wild horses by capture and adoption, populations had risen across the West, from 17,000 in 1970 to 48,000 in the mid-1980s. The horses outcompeted commercial cattle that shared their rangeland, scouring landscapes of edible greens. Ranchers complained, so Interior Secretary James Watt exploited legal loopholes that allowed them to sell wild horses for slaughter. The public, which had eschewed contraception, finally began to embrace it as a lesser evil.

Kirkpatrick was still struggling with steroid contraception when he learned in 1988 that Irwin Liu, a veterinarian at the University of California at Davis, had quietly begun working with what might be the ideal tool: a failed human contraceptive called porcine zona pellucida, or PZP.

PZP provided a fresh approach to contraception—a vaccine that harnessed immune cells to prevent pregnancy. Zona pellucida proteins distilled from pig ovaries were injected into horses, and these foreign proteins prompted the horses’ immune systems to manufacture antibodies against them. Those antibodies latched onto the surface of newly ovulated horse oocytes, blocking sperm from entering the egg.

When Liu tried PZP in 14 captive horses, it prevented pregnancy in 13 of them. And, unlike steroids, PZP worked in small enough doses that Liu could inject it through a dart fired from a rifle. So in 1988 Liu, Kirkpatrick, and Cornell classmate John Turner of the University of Toledo College of Medicine packed their rifles and headed to Assateague Island off the Maryland coast to try PZP on wild horses.

The results exceeded their expectations. Just 4 percent of vaccinated mares produced foals in the year after darting—compared to 45 percent of unvaccinated mares. Liu and his colleagues published the results in Wildlife Society Bulletin in 1990, and their world changed overnight. “All of a sudden, my phone rang in my office from eight in the morning until the time I went home,” says Kirkpatrick. “The reporters were on the phones, the animal welfare groups were on the phones, and the zoos were on the phones. It was just pure excitement.”

Buoyed by success, Kirkpatrick the Dartman spent weeks each year prowling the bushes, vaccinating horses and deer through his rifle at 40 paces. Back in Billings, he scaled up laboratory production of PZP. He left Montana State and founded The Science and Conservation Center in Billings. With two employees and the help of Turner, he now converts 200 kilo-grams of pig ovary into 5,000 doses of PZP each year. Kirkpatrick himself has darted over 5,000 animals in 19 years—mostly wild horses and white-tailed deer, with occasional forays into more exotic beasts like water buffalo and bears.

But the epiphany that spawned elephant contraception arrived back in 1984. Television personality Roger Caras interviewed Kirkpatrick and Turner for a wildlife documentary. As he watched the program in his living room a month later, he was shocked by what he saw. The show opened with footage of elephant culling in Kruger National Park: female elephants and their nursing calves crumpled side by side as shots rang out. The documentary then transitioned to Kirkpatrick’s work with wild horses, and Caras asked, could animal contraception solve the elephant problem without bullets?

“I didn’t even know they did elephant culls,” recalls Kirkpatrick. “Caras made the connection. That was the birth, in my mind, of elephant contraception.” Kirkpatrick lacked the technology, but the idea of contracepting elephants stuck in his head. The advent of a workable vaccine a few years later made it possible. So in the mid-1990s, Kirkpatrick began working with Henk Bertschinger, a reproductive biologist at the University of Pretoria in South Africa. And porcine zona pellucida, dissolved in sterile water with Freund’s adjuvant, arrived on the African savanna.

Kirkpatrick and Bertschinger fired the first darts in South Africa’s Kruger National Park. From 1996 to 2000, they studied the effects of PZP in 31 of the park’s 11,000 elephants. A year after the first dose, 44 percent of vaccinated elephants had fallen pregnant, compared with 89 percent of unvaccinated elephants. By adjusting the darting schedule, they lowered pregnancies to 20 percent.

PZP studies also continue at the much smaller Makalali Reserve, where 73 elephants roam 22,500 hectares of bush. All female ele-phants were vaccinated from 2000 to 2005, and not a single calf was conceived. Managers have since eased back on vaccinations, allowing 2 to 3 percent annual population growth. Bertschinger now produces PZP locally; he and van Altena dart elephants at nine game reserves and parks across South Africa. In a small population where individual elephants are known, “We can actually play God” and decide which females conceive and when, says Audrey Delsink, who studies the social impact of contraception on Makalali’s elephants. It’s an awesome power—and it provokes a profound question: why regulate wild populations that have ostensibly managed themselves for millennia?

The answer lies in the shrunken geography of the modern herbivore’s world. Prior to European arrival, water regulated elephant populations. Unusually dry years forced ele-phants to venture farther from rivers to find food, and calves foundered during those thirsty treks. But even large parks like Kruger now augment natural rivers with water holes supplied by wells. These water spots improve tourists’ odds of sighting Africa’s “big five” game, since animals congregate there, but they also guarantee that elephants can reach any corner of a reserve without straying too far from water.

“Where you would normally get losses of young calves in very dry seasons,” says Bertschinger, “you can now move from one water hole to the next one.” Elephant populations can grow 10 to 12 percent annually in smaller reserves, where fences restrict wildlife from wandering far from water.

Water holes drilled to support herds of cattle and sheep across the rangelands of Australia have also spawned hordes of kangaroo that compete for the same resources—prompting an annual cull of Australia’s most iconic marsupial. North America’s quilted suburban landscapes also provide food and water (often free of predators) to deer who then throw it all away in one mad instant by dashing in front of a minivan.

The common theme is human-sculpted landscapes benefiting some species over others, says Chris Wemmer, scientist emeritus at the National Zoo in Washington, DC. “You get one species thriving and the normal predator isn’t there,” says Wemmer. “It’s a very widespread phenomenon. It’s happening around the world.”

Yet the magnitude of the demand for contraception pushes up against some harsh realities. It’s easy to understand the appeal of contraception to a community overrun by deer when you consider the alternatives: poisoning, shooting, or costly roundups in the vicinity of homes, schools, and strip malls. The same goes for elephants, which South Africa’s urbanites increasingly view as sentient, emotional creatures. But despite the promise of miracles, contraception can do only so much.

Elephants often live 60 years, so even complete contraception would require 15 years to reduce an overgrown population by 25 percent; in the meantime, those overabundant elephants might devour every green thing in sight. And no biologist in his right mind would maintain elephants for a decade and a half at 100 percent contraception; doing so might disrupt the social fabric of pachydermdom. “Having absolutely no babies for an indefinite period of time is detrimental,” says Delsink, “not only to the social dynamics of the herd, but also to the population structure.” Elephant parenting skills are known to develop as juveniles look after younger siblings—a process which 15 birthless years might interrupt. It was this sort of consideration that led Delsink and van Altena to ease up on contraception at Makalali in 2005 and allow elephant numbers to grow by 2 to 3 percent per year rather than by zero percent.

That growth rate represents a compromise. It’s well below the nine percent growth seen at Makalali before contraception—but it could still necessitate the removal of a few animals sometime in the future. In reserves that have already hit their carrying capacity for elephants, contraception will almost certainly have to be combined with culling.

Similar limitations apply to deer in North America. Although deer control remains a goal in dozens of states, contraception will never keep the lid on 25 million deer. Bullets can whittle down deer numbers in a way that darts can’t, and people are lining up to pay license fees for the privilege of doing it. “It’s much cheaper,” concludes Turner, “to put a bullet in a deer than it is to contracept it.”

Hunting, capturing, clubbing, and poisoning don’t work as well in suburbs and small parks, though. It’s these places, where wilderness mingles with humanity, that contraception makes the most sense. Targeting the suburban deer demographic could translate into contracepting 20,000 to 50,000 does across the U.S., says Allen Rutberg, who collaborates with Kirkpatrick, Turner, and Liu from his post at the Tufts-Cummings School of Veterinary Medicine in Boston. That might mean treating deer in several hundred locales across the U.S., a few dozen to a few hundred animals per site.

The labor of darting that many animals presents the largest technical hurdle. Plenty of studies have found PZP effective if it’s scrupulously applied to most of the females. Yet horses, deer, or elephants were traditionally darted with PZP twice in the first three months followed by annual boosters. It can be a lot for cash-strapped local governments to accomplish.

But newer work presented at the September symposium in York shows progress in making contraception less labor-intensive.

One strategy is to create vaccines that last longer. At the meeting, Turner, Rutberg, and Liu presented the latest results for a controlled-release formulation of PZP intended to provide 2 years of contraception with a single dose. “The long-term goal,” says Turner, “is to get a vaccine that will last three or four years.” Lowell Miller at the USDA’s National Wildlife Research Center in Fort Collins, Colorado, showed early results for a newer controlled-release vaccine against gonadotropin-releasing hormone (GnRH). The vaccine prevents estrus, ovulation, and mating. Because GnRH is grown in recombinant bacteria rather than derived from animal tissue, as PZP is, its use may present fewer governmental regulatory hurdles than PZP in the long run.

Miller’s group is also preparing to test an oral formulation of GnRH; an oral vaccine would carry huge implications. Rather than darting animals one by one, wildlife managers could mix the vaccine into bait, then wait for their quarry to come and eat it.

The drawback is that GnRH and PZP work in hundreds of mammal species—and some nontarget species will inevitably consume the vaccine from bait stations. But Miller’s team is working on that problem with DiazaCon®, a failed human cholesterol drug which they’re testing as an oral contraceptive in birds. They’re developing bait stations which they hope will specifically deliver DiazaCon to monk parakeets in Florida by relying on that species’ unique combination of strength, dexterity, and beak size. Similar strategies might eventually work in mammals, says Miller.

Others have explored more-aggressive approaches to species-specific contraception. Christopher Hardy and Lyn Hinds at the CSIRO Entomology Division in Canberra, Australia, experimented with recombinant versions of cytomegalovirus and myxoma virus, which express key reproductive proteins when they infect invasive mice and rabbits. The viruses rendered lab animals sterile. Australian authorities might have released such viruses into the wild to propagate and spread—a prospect that provoked plenty of concern—but as of last month’s York meeting, the project was discontinued for technical reasons. Across the Tasman Sea, Phil Cowan of Landcare Research in Palmerston North, New Zealand, is still developing genetically modified parasitic nematodes to sterilize invasive brushtail possums.

But never mind viruses. Even tried-and-true dart contraception still encounters plenty of knee-jerk resistance.

The lengthy debate over contraception has exacted a very real cost: population problems continue to worsen as time passes. Wild-horse populations have doubled in the past four decades. Efforts to contain horse numbers still emphasize yearly roundups and adoption of as many of the collected horses as possible. Unadopted horses are maintained at taxpayer expense on privately run reserves in Oklahoma and Kansas. The number of horses thus living on the government dole currently stands at 22,000.

BLM now performs some contraception—about 500 horses per year, out of 30,000 on public lands—but it took decades to happen. Hall, the BLM man who first roped Kirkpatrick into contraception 36 years ago, eventually made his way to the National Wild Horse and Burro Program in Reno, Nevada, where he pushed hard for contraception before retiring in 2004.

Contraception of deer stands at a similar crossroads, with a few hundred currently treated out of the many thousands of possible recipients. Hunters and the state agencies who license them remain suspicious of contraception to control suburban deer, which they fear—realistically or not—could someday replace hunting in open wilderness. And even as elephant contraception proliferates among small game reserves in South Africa, large parks like Kruger remain aloof to the idea.

“Right now we have the technology to solve 50 percent of the problems that this stuff was designed for,” says Kirkpatrick. “And we can’t get near that 50 percent because the real issues are social, cultural, political, and economic.” Perhaps that’s the nature of family planning.

About the Author

Douglas Fox is a freelance writer based in San Francisco. He has written for New Scientist, Natural History, and Discover and is a frequent contributor to Conservation.

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