Thousands of bats protected during hibernation
10/04/04 12:00AM By Steve Zind  Download MP3
(Host) Bats have long been popular objects in horror and Halloween tales. But their frightening image belies a graceful creature that plays an important role in our ecosystem. Scientists have long puzzled over the why there's been a steady decline in the number of bats. Now, work being done to study and preserve an important bat habitat in Vermont may ultimately provide answers.
VPR's Steve Zind reports.
(Sound of footsteps on rocks and people talking.)
(Zind) A steep and rocky road climbs through the hardwood forest that covers Mount Aeolus in Dorset. It winds past tailings from old marble and limestone quarries. Occasionally, a clearing appears and there's a startling view of the darkening valley below. Near the top of the mountain a short side trail leads to the left.
"The light is starting to wane here under the tree canopy and we can see that the bats are just starting to get active, they're just starting to wake up."
(Zind) Darkness comes quickly and with just a half moon for light, it's hard to tell if the small black shapes flitting overhead are real or imagined.
A flashlight beam illuminates a rock-strewn hole in the mountainside. This is the entrance to the Dorset bat cave. It's the winter home to more than 20,000 bats and the largest bat hibernaculum in New England. The bats whirl in a vortex that rises from the cave.
(Rose) "You don't have to duck or swat or anything. They're quite capable of avoiding us and they don't particularly want to land on us or in our hair or anything like that. They just ignore us and go about their business and we should do the same."
(Zind) Rose Paul is with the Nature Conservancy of Vermont which owns the land the cave is on. As the evening passes, the cloud of bats swirling from the cave entrance becomes denser.
(Rose) "We're here at the mouth of the cave and set in just a little bit is the new gate. Would you like to see that?"
(Zind) A steep pitch leads into the cave.
(Sound of someone slipping on rocks.) "Are you okay?"
(Zind) Water drips from overhead. The ground is slippery and footing is difficult, especially in the dark with flashlights extinguished to keep from confusing the bats.
Twenty feet into the cave a sturdy gate blocks the way. The newly installed steel bars allow the bats to fly out and prevent people from entering, protecting the bats from being disturbed once they go into hibernation.
A cacophony of high-pitched squeaking comes from inside the cave. Unlike the ultrasonic sounds bats make to locate objects as they fly, these sounds are easily audible. It's a form of bat communication.
"They are chattering. Who knows what they're saying?"
(Zind) There is another, much closer sound in the darkness: the soft flutter of wings. Bats are pouring out of the cave. Occasionally, there's the soft touch of a wingtip against a cheek or an arm, but nothing more.
A flashlight is turned on for a few seconds. The air is alive with bats, swirling within inches of the two crouching figures. Far from their image of fang-baring predators these bats seem gentle and graceful.
Six species of bats inhabit the Dorset cave in the winter, including the federally endangered Indiana bat. This time of year the bats are swarming to mate. Soon, they'll begin to hibernate, eventually moving deep into the cave where the temperate remains a constant 43 degrees. Scott Darling is a state fish and wildlife biologist.
(Darling) "Caves and mines that serve as bat hibernacula during the winter periods are just very valuable, critical wildlife habitats. These are one of the key predators of moths, beetles, many of these species that these bats feed on are actually agricultural pests."
(Zind) Darling says the state has installed monitors in the cave to record the temperature and humidity. They're part of an array of equipment biologists use to study the bat population.
(Darling) "What this is, is a bat detector, which is an instrument that can pick up and relay the high frequency calls, or the echo-location calls of bats. And it's an important instrument with bat biologists because it enables us to do what we call acoustic monitoring, which is to identify the number of bat calls that are made to have some relative index of abundance of bats. But we can also download this information onto a computer that actually enables us to visualize the bat calls, the echo location calls, and in many cases distinguish the various species of bats simply by the appearance of their calls on the computer screen. Feel the wing go by? That went right by you!"
(Zind) Dorset cave has long been known to scientists. It's one of 23 known bat hibernacula in Vermont and by far the largest. In the 1930s a Middlebury College zoologist reported huge swarms of bats leaving the cave. But bat numbers are fewer now, here and elsewhere.
(Darling) "On a national level, bat populations are declining and there's great concern about many of these species, simply because they have such low reproductive rates."
(Zind) Darling says there's still too little known about bats to determine what's causing the decline.
The Nature Conservancy acquired the Aeolus Mountain land in 1983 to protect the bat habitat. Rose Paul says for many years the cave was open in the summer. Several hundred feet long, it was a popular spot for novice spelunkers. But three years ago a new passageway was found.
(Paul) "It suddenly flipped from being a beginner's cave to a real expert cave. It's very deep with some very skinny passages. It's a dangerous cave to be in if you don't know what you're doing."
(Zind) So far cavers have explored 3,000 feet of Dorset cave, making it the most extensive limestone cave in New England. Those who have been far into the cave say there are two large chambers, each about 100 feet long and 300 feet high. And there could be more to explore.
The cave's new entrance gate will be locked from the beginning of September until the end of May. This winter the Nature Conservancy says it will create a management plan to protect the cave. Cavers say they hope the plan will still allow them to enter during the summer. The Nature Conservancy says it wants to find a way to allow exploration of the cave's depths without disturbing its valuable inhabitants.
For Vermont Public Radio, I'm Steve Zind.