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October 2019
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To ensure bison health and to protect Catalina’s ecosystem, Catalina’s bison population is closely monitored and managed by the Catalina Island Conservancy and the herd size is held at just about 150 animals. Limiting herd size to limit soil compaction and habitat degradation, and to keep our bison healthy, is especially important to the Conservancy. After all, Catalina is home to more than 60 plants and animals found here and nowhere else in the world! Bison, a non-native species on Catalina, need to be managed in a way so they have enough food to stay healthy while protecting native wildlife and habitats.

In 2009 the Conservancy embarked on a scientific first for the Island, and for any other herd of wild bison in the U.S.: bison contraception.

The Conservancy’s contraception plan includes an annual “inoculation” of all female bison at least two years old with the Porcine Zona Pellucida vaccine (PZP). PZP derived from pig eggs, is injected into the muscle of a female bison where it stimulates the immune system to produce antibodies against the vaccine. These antibodies attach to the sperm receptors on the surface of the female’s eggs, and block fertilization.
Issue #1 / All About Bison

History on Catalina
By the numbers
Secret sex lives
Fact or Fiction?
Did you know...

The inoculation is non-hormonal, is safe for the animals, and will not negatively impact their social structures or behaviors! So far, the most obvious change for the bison is that their breeding season appears to be extended since females that don’t get pregnant stay in estrous longer. (Yes, that means more sex for Catalina’s bison!)

The PZP vaccine was developed for human use and is well tested and safe, but is only 90 percent effective in preventing conception. Because of this, it proved unsuitable for human use that requires solutions to be 99 percent effective. For the Conservancy’s bison management goals, however, 90 percent efficacy is more than adequate, since some births need to occur to account for deaths and keep the herd size stable. As an added benefit, contraception using PZP is reversible, so that the Conservancy has the ability to increase herd size when needed.

The results of the Conservancy’s bison contraception program are very encouraging: staff have found only one calf in the 2011 calving season (as of mid-June), where 27 calves had been born at this time in 2010. Conservancy biologists are confident that contraception will provide the most humane, cost-effective and bison-friendly alternative for keeping herd numbers at an ecologically sustainable level!
Did you know that Catalina’s bison are smaller than those that live on the mainland? Find out why in this month’s “Fact or Fiction” feature, click here.

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