There are roughly 8,000 mountain caves in the eastern U.S. state of Tennessee, and a small percentage of them are home to the endangered gray bat. So, environmentalists and government scientists are building gates over eight cave entrances. These barriers would protect the thousands of bats inside, by preventing people from entering the caves and disturbing the sensitive creatures. But, the proposed gates have angered some other devotees of the dark local spelunkers who say their right to explore the caves must also be protected.
When people think of a gated community, they usually imagine a suburban subdivision, not a dark cavern filled with endangered animals like gray bats, blind crayfish and cave beetles. But on a piece of federally-owned land, the Nature Conservancy, the Army's Corps of Engineers and the U.S. Fish and Wildlife Service recently joined forces to build gates across some cave entrances. The barriers are there to protect thousands of gray bats that raise their young inside each summer.
During this critical period, an intruder entering the cave could frighten bat mothers and cause them to drop their young from the cave's high, domed ceiling. Panicked bats might even desert the cave all together. Just one human disturbance can disrupt, or destroy an entire colony. In the winter, hibernating bats can end up starving if they waste precious energy scattering from intruders. So, conservationists say keeping humans out of caves during the summer and winter is not just desirable but necessary to the bats' survival.
At the base of a hole about the size of a car, gate designer and builder Roy Powers works with his assistant Kristin Bobo. At this site, gray bats have to fly straight up to exit the cave. Given that colonies of between several thousand and a quarter of a million bats need to exit the cave freely en masse, this opening requires a chute type design called a cupola. At 12 meters wide by three meters tall, the rectangular chute looks like the opening of a large elevator shaft. Or one can imagine the chute as a giant chimney, and the gray bats as smoke. Assistant designer Kristin Bobo says the design meets the bats' needs.
"Gray bats don't like these vertical bars so we put a big open chute on it so they can fly out free and they don't have to go through bars. And we angle it in such a fashion, we use really sharp expanded metal so people can't crawl on it. It's very flimsy if they tried to grab it, it would cut their fingers and flip them off, anyway because it's very flimsy. So the bats love these gates. We use the cupala design on vertical entrances sinks and pits," Ms. Bobo said.
Creating vandal-proof steel gating to protect the bats might seem simple until you factor in that large numbers of bats need to come and go to feed on bugs at night. For Roy Powers, designing such a gate has been a real learning experience. Mr. Powers has made cave gates for 24 years has patented several of his designs.
"Twenty something years ago we didn't really know what the criteria for a bat friendly gate was and we didn't really know what the criteria for a bat-friendly gate was and we had a lot of gates that caused huge population decreases. As a matter of fact in some caves, bats totally abandoned the cave. We're beginning to understand that now," Mr. Powers said.
One design element that hasn't changed over the years is the vandal-proof reinforced steel beams that Kristin Bobo and Roy Powers use on their chutes. But these gates don't only keep vandals out, they keep everyone out. This includes experienced spelunkers. These cave-exploring enthusiasts say they know to stay out of bat inhabited caves in the summer and winter, and they are angered by the new cave gates. Bill Overton, the current chair of Nashville Grotto, a local chapter of an international caving organization, says he is not surprised that cavers have directed some of their anger at gate designer Roy Powers.
Mr. Overton recalls one recent incident in which some outraged Grotto members threatened to vandalize some gates. He says they didn't act on those threats, but he understands their frustration. "Wolf River cave a couple of years ago was gated. It's a very popular cave. There were good reasons for gating it. There are endangered bat species in the cave that need to be protected. Cavers typically don't like to be told which caves they can or can't go to. Granted there's thousands of caves, but you usually don't gate the grunge holes. You gate the nice ones to protect them," he said.
Most cavers want to protect endangered bats, but still have access to their favorite caves. So a compromise was worked out at several of the sites gated by the Nature Conservancy: qualified spelunkers may explore the caves, by appointment only. Mr. Overton says the compromise has inspired the Nashville Grotto to become a partner in managing the region's bat caves.
"We have two of them in Davidson county that are gated with controlled access. We have been very careful to keep an open cave policy. Anyone who wants to get in our cave, if they qualify with a helmet, and safety equipment, then they can get in. We have a form that they have to read over and agree to and sign a release and we are doing 500 to 600 people a year in these caves. So you can have an open cave policy even though the cave is gated. But it's a challenge," Mr. Overton said.
Cave gates may bother cavers, but they seem to be a hit with bats. Many experts believe the gating efforts are an important factor in the recent rebound in the gray bat population. Designer Roy Powers agrees.
"When we get these kind of caves, we see the populations increase. As a matter of fact, with the gray bats, which is what we've got here, we're thinking about, or the Fish and Wildlife is thinking about, knocking them down a notch from 'threatened' to 'a species of concern.' So, it's worked," Mr. Powers said.
There have been no official studies yet on the effectiveness of cave gates, but experts say there is little doubt that the gray bats in this area are benefiting from measures to protect their privacy during vital winter and summer months.