WASHINGTON, Dec. 16 (UPI) -- The U.S. National Park Service says birth control has not been effective at reducing the number of wild ponies on Maryland's Assateague Island.
That's because female ponies, no longer stressed by constant childbearing, are living longer, The Washington Post reports.
The island now has about 140 ponies, up from 28 in 1966 and down a bit since the birth control program began. While the ponies are the island's most famous wildlife, they are descended from horses introduced in the 17th century and are not native.
The ponies are devouring native plant life, including the native grasses that hold Assateague's dunes and thus the island in place.
Officials say that killing ponies is not on the table. But they are considering sending some of them to the mainland to sanctuaries where they can live out their lives away from the cordgrass, the Post said.
Animal rights activists want the ponies to stay, arguing that the birth control program is working, even if it is slow.
