It all began with a deer on the cover of All Animals magazine. Terry Kline, administrator of the Botstiber Foundation outside Philadelphia, saw the photo in the spring of 2014 and turned to a feature about managing deer populations with fertility control. For years, Kline had been frustrated that annual deer culls in Ridley Creek State Park were promoting recreational hunting in a small park surrounded by suburban homes with young children, rather than resolving conflicts between humans and deer. Two of the three townships that govern the park had already voted to end the hunt, and a Penn State University philosophy professor, Priscilla Cohn, had waged a campaign against it. In 1987, Cohn helped organize the first international conference about an alternative to culling: wildlife fertility control. But still every year the Pennsylvania Game Commission allowed hunters to shoot deer in the park.

Image of the All Animals magazine article, "Out of season"

The All Animals article described successful deer fertility control programs, including darting deer with PZP, a contraceptive vaccine the Humane Society of the United States helped develop that works for many species. Kline saw a safer and more effective means of managing the deer population in Ridley Creek State Park. He contacted the HSUS and was referred to Stephanie Boyles Griffin, then senior director for wildlife innovation and response. Two years later, money from the foundation launched the Botstiber Institute for Wildlife Fertility Control, with Boyles Griffin as science and policy director. Through events, research and public policy grants and public education, the institute helps steer communities and governments away from killing and toward more effective and popular nonlethal methods of preventing human-wildlife conflict.

“It’s a shift globally in public values and attitudes about wildlife away from utilitarianism and towards mutualism,” says Boyles Griffin, now senior scientist and wildlife protection program director for the HSUS. “It’s got its own momentum. We’re just trying to be the catalyst.”

This year, as the institute celebrates its fifth anniversary, it is expanding its geographic reach and supporting research that promises to help resolve longstanding human-animal conflicts.

It’s a shift globally in public values and attitudes...

Stephanie Boyles Griffin, The HSUS

This fall, the institute, in partnership with the University of York, will launch the Botstiber Institute for Wildlife Fertility Control Europe. Giovanna Massei, a leading fertility control researcher, will serve as director from an office in the United Kingdom. There, the issue is finding humane methods to reduce the number of gray squirrels. Introduced from the United States, gray squirrels now number more than 2.5 million in the U.K. The native red squirrel population has dwindled to fewer than 200,000. Rather than killing gray squirrels, researchers supported by UK Squirrel Accord are developing a bait that will keep them from reproducing and feeders that deliver the contraceptive to gray squirrels only.

Next year, the institute will host the ninth International Conference on Wildlife Fertility Control. The event will focus on animals at risk in places like the American West: prairie dogs, who are killed as pests, and wild horses, who the Bureau of Land Management continues to gather and send to holding pens.

PZP-22, developed for wild horses and deer, prevents mares from becoming pregnant by provoking an immune response. In vaccinated mares, antibodies to pig ovary (porcine zona pellucida) proteins bind to receptor sites on the surfaces of eggs, preventing sperm from fertilizing them. One dose of PZP-22 works for one to two years. If mares get a booster, PZP-22 works for three to five years. But locating and darting mares a second time is challenging in remote and rugged territory. So the agency is looking for a longer-lasting contraceptive vaccine.

Photo of hand holding a vile of PZP
The PZP vaccine stops deer from getting pregnant.
Galen Clark
For the HSUS
Photo of a tagged deer
Female deer in a New York City suburb are tagged to show they have been injected with PZP.
Robert Caplin
For the HSUS

Researchers affiliated with the institute are developing a “next-generation” version of PZP with recombinant technology. A team led by Harm HogenEsch of Purdue University, an immunologist who serves on the institute’s board, is taking genes that encode for the PZP pig ovary proteins and placing them in bacteria to grow synthetic pig ovary proteins that are humane and can be shipped around the world without violating import or export restrictions.

HogenEsch’s team is also trying to develop a new ingredient to cause a longer-lasting immune reaction in mares. If that’s not possible, they will find a way to delay the vaccine’s release in the mares so it’s effective for three to five years. Boyles Griffin is hoping the new, improved PZP could end the BLM removing wild horses from the range.

“It would be revolutionary,” she says. 

Beyond country-specific human-wildlife conflicts, the institute is encouraging research into fertility control for a species multiplying worldwide despite hunting: wild boars. As with gray squirrels, scientists are developing contraceptive bait. They’ve already invented a method to deliver it—a heavy metal “bell” that covers the bait and can only be lifted by pigs rooting for food. An institute-sponsored webinar in June brought together researchers and experts from the U.K. (including Massei), France, Hungary, India and the United States, including Dave Pauli, HSUS program manager for wildlife conflict.

Pauli says the time is right for wildlife and property managers to adopt fertility control: “Humans cannot kill their way to success.”

Late in 2020, hunters again killed deer in Ridley Creek State Park. Around the same time, the Botstiber Institute organized a webinar by Anthony DeNicola, an expert in surgical sterilization of deer. In less than five years, fertility control can reduce deer populations in suburban communities, DeNicola told the audience. The institute continues to spread the message. Eventually, even in Ridley Creek, culls will end.

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