Researchers say a species of bat once near extinction may be thriving in two Tennessee caves.

The Middle Tennessee caves are hibernating sites for the gray bat, a Southeastern species that's been on the federal endangered list for decades, the Knoxville (Tenn.) News Sentinel reported Monday.

Researchers recently counted substantially more hibernating gray bats in each cave than in 2002. The first cave had 144,558 gray bats, a 58.7 percent increase, while the other cave went from 156,000 hibernating gray bats in 2002 to 519,570 this winter.

The Nature Conservancy's Tennessee chapter told the newspaper the bats in one cave responded well to a 25-by-30-foot steel gate built in 1985 near the entrance to the cave. The gate permits the bats to come and go, but limits public access while the bats are hibernating.

The Nature Conservancy is among a number of public and private conservation groups working with the federal government to determine if the gray bat population is healthy enough to be removed from the endangered species list -- an event scientists say is nearly unheard of in endangered species listings in the United States.

Copyright 2006 by United Press International