Biologists use birth control to manage Catalina bison population

AP Photo

A bison rests on a hilltop in this Feb.6, 2002 file photo, near Avalon, Calif., on Catalina Island. Bison were imported to the Island for the sake of a movie in which they never appeared. Long thought by some to be genetically pure, the wild bison of Santa Catalina Island in fact have traces of cow DNA, the first genetic analysis of the animals found.

Biologists undertook an unusual operation today to control the bison population on Catalina Island. They injected female bison with a vaccine called PZP (Porcine Zona Pellucida) that prevents pregnancy.

The injection causes the bison to build up antibodies against the vaccine. The antibodies then attach to the outer membrane of the female's egg, preventing sperm from fertilizing the egg.

At one time, about 600 bison roamed the island. Scientists want to keep the number of bison between 150 and 200.

(Audio: KPCC's Alex Cohen spoke with Dr. Ann Muscat, president and CEO of the Catalina Island Conservancy, about the contraception program.)