You see buffalo all over the west (just stop by Custer State Park in South Dakota), so it's hard to think of them as endangered. But apparently there are only 20,000 in wild. The rest are behind fences, according to a story on Thursday by the Associated Press.

Now, environmental groups have filed notice they plan to sue the federal government to force officials to grant federal protections to plains bison as an endangered species. The groups argue that bison numbers have been decimated in the last two centuries from a population that once roamed the country.

The notice was filed by the Center for Biological Diversity and the Western Watersheds Project. The federal government has rejected an earlier petition.