The animals, commonly called American buffalo, are starting birth control Friday as part of a five-year experimental program to control the population. Apparently abstinence-only education wasn't working.
Because they don't make the NuvaRing for bison, the female members of the herd will be given a non-hormonal product called PZT, an annual vaccine derived from pig eggs.
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"Bison will continue to be bison. Males will continue to compete for females, and females will continue to go into heat. The only difference is that we can control how many calves they have," de la Rosa told the Associated Press.
"For bison in love, this means romance without responsibilities," he said with a laugh.
The bison were first introduced to the island back in 1924 for a silent movie called "The Vanishing American," according to the Conservancy, a nonprofit group that owns much of the island. After filming, the bison were left behind.
The heard peaked around 600 members, and as of 2003, there were about 350 bison on the island, the AP reported. Conservationists want to keep the population between 150 and 200 animals, according to the Conservancy.