A Nevada legislative mandate to seal some 3,000 abandoned mines in Nevada threatens bats that roost in the shafts. Biologists who study bats say that as cave exploration has grown in popularity, "cavers' have scared bats out of their natural habitat. Many now take refuge in abandoned mines. At a recent workshop with Nevada officials and mining company representatives, biologists proposed installing gates in caves to bar people but not bats. Stopping up all mine mouths with dirt might halt the growing number of injuries and deaths at abandoned mines, biologists said, but it would also devastate bat colonies. Twenty-nine species of bats in Nevada are already listed as endangered. According to Christopher Henry, of the Nevada Bureau of Mining and Geology, gates won't save the habitat of bats forever. He says many of the state's abandoned mines are deteriorating rapidly, and "the underground mines that exist today aren't going to be here in a thousand years."