SOUTH LAKE TAHOE, Calif. – A vaccination called PZP could be a potential solution to stop mother bears teaching their cubs to break into houses, according to the BEAR League. Executive director Ann Bryant says she’s spoken with the Science and Conservation Center (SCC) in Montana, which provides PZP to zoos and organizations that manage wild animal populations.
Last summer, bear #753, also referred to as Hope, was responsible for several entries into properties along with her cub, sometimes called Bounce. The California Department of Fish and Wildlife (CDFW) ordered that she should be killed to prevent further human-bear interactions, one of the many ways that the CDFW manages bear populations.
The BEAR League was vocally opposed to the killing, and the city of South Lake Tahoe decided in December of last year to establish a collaborative response protocol group including the city police department, bear groups, the CDFW, South Tahoe Refuse, homeowners associations and other interested parties.
At the last city council meeting in March, Bryant spoke during public comment and said they had buy-in from the SCC, Oakland Zoo and California Conservation Society to potentially launch a pilot program to use PZP on Hope.
Bryant said that the CDFW and BEAR League agreed that the majority of break-ins were from mother bears with dependent cubs, who then transmit that behavior to their cubs. If they have female cubs, then that negative behavior continues to be transmitted to cubs.
So, by targeting sows who display this unwanted behavior, it would stop them from continuing the cycle of bears learning to forage in human environments. Many other behaviors are also related to raising their cubs, such as seeking shelter in human environments to escape aggressive male bears or seeking out easier foraging sources while pregnant or teaching their cubs—these could potentially be stopped as well.
The SCC works with the Association of Zoos and Aquariums (AZA) and internationally to provide PZP to zoos, providing reproductive management to zoos with animals that should not be breeding in captivity. They also provide the PZP vaccination to manage wild populations of ungulates like deer and horses.
PZP, short for Porcine Zona Pellucida, was developed in 1988. The zona pellucida is a protein that surrounds the egg and receives sperm to fertilize it. By injecting a female animal with PZP, a pig (hence porcine) zona pellucida is introduced into the target animal’s body. This triggers an immune response where the target animal’s immune system will respond, producing antibodies that then attach to their own zona pellucida, preventing their eggs from being fertilized.
The vaccine must be administered annually and has a 90% or greater efficacy with hundreds of different species. It has also been proven to be safe to give to pregnant and lactating animals, shows no debilitating health side effects even with long term use, does not impact social behaviors and cannot pass through the food chain. Even if an animal were to eat another that was treated with PZP, they would not have the immune response triggered by its passage through the digestive system.
“We have found it works amazingly well with bears with 95 to 98% efficacy,” said Kim Frank, executive director of the SCC. “We have seen with bears in zoos that after they’ve been on the vaccine, that if we discontinue the treatment, they return to normal fertility in one to three years.”
Frank continued, “The plan in South Lake Tahoe as I understand it, is that they would not try to decrease the population of black bears, just prevent sows from teaching their cubs to break in.”
Bryant believes that by using bear #753 as a pilot, they could protect her from being killed and could observe the impact that PZP could have in a wild population of bears. “With our background and our network, we have the ability to study this, and it has been shown to be reversible—so there would be no long-term negative effects,” said Bryant. “We are not tampering with the bears’ natural biology, and they will still go into estrus, mate and so on. They would just be unable to conceive cubs if treated with PZP.”
The pilot program with wild bears would be a first for the SCC, as it has previously only been used in bear populations in zoos.
The SCC provides PZP to the Bureau of Land Management (BLM) and its partners in non-governmental organizations (NGOs) to manage wild populations of horses and deer throughout the west, including in Montana, Wyoming, Idaho, Utah, Arizona and Nevada. In Nevada and Arizona, NGOs have a memorandum of understanding with their state departments of agriculture, showing that a partnership with state departments is possible.
Frank says that such buy-in from stakeholders is key to making these kinds of programs work. “In all the years I’ve worked on this, I see everyone wants the same end—a healthy ecosystem and healthy animals,” she said. “I want to see openness to potential solutions for problems. And I understand that killing is one solution, but this is something that could work. Why not try it?”
Bryant feels a sense of urgency around the potential pilot program, as the breeding season approaches and bear #753 will leave her cub. She knows that to make this program work, they would need buy-in from the CDFW as well. But she worries that the state department will move too slowly to make it a reality. “We are almost out of time,” said Bryant, who says they have been talking about the potential of such a program since fall of last year.
“If we don’t do anything, what is the point? We keep the status quo of killing bears?” asked Bryant. “Killing bears is not ending the cycle. This has a huge opportunity to resolve the issue, even if it won’t be a quick fix. And if we work together, the world could benefit from the work we do with a wild population.”
Bryant hopes there will be community support for this novel, potential solution. She also hopes there will be support for making South Lake Tahoe a bear-safe or bear sanctuary city, which she clarifies would mean the city would seek out non-lethal solutions for managing bears.
Bears are on the agenda for the upcoming city council meeting on April 21, where police chief Jeff Roberson and sustainability coordinator Sara Letton will report on the collaborative bear process and protocol.
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