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Maiden Rock/Bay City bat caves house 150,000

As the weather cools, upwards of 100,000 bats will make their way into the Wisconsin Industrial Sand Corp. mine in Maiden Rock to hibernate for the winter months. Their hibernaculum is in the oldest part of the sand mine, which no longer is actively worked. Bats huddle together for warmth on the high sandstone walls and ceilings of tunnels beneath about 30 acres in the Maiden Rock area. Another 50,000 bats can be found nights in the Bay City sand mine a few miles away. Cody Buckalew / RiverTown...1 / 2
Tim Stauffer shines a light on brown bats in the Maiden Rock sand mine. Cody Buckalew / RiverTown Newspaper Group2 / 2

MAIDEN ROCK -- It's cold. Dark. Quiet as a tomb -- except for little squeaking sounds so tiny you wonder if you're imagining them.

It is Halloween, after all.

A small, furry creature abruptly detaches from the high sandstone wall and swoops away, down an even darker tunnel in the Wisconsin Industrial Sand Corp. cave.

Silently -- except for tiny little squeaking sounds.

Tim Stauffer, regional manager for mine owner Fairmount Minerals, shines a spotlight on a strip of brown on the wall. It moves, almost imperceptibly.

One of the little browns hasn't quite settled in for the winter, although some of the others already are covered in condensation that will keep them hydrated for the coming months. He pops his head up for a moment, then settles back into the huddle.

Warm weather this past week has meant an unusual amount of activity for the 100,000-plus bats that stay at the Maiden Rock "bat hotel"

over winter. It's one of the largest bat hibernaculums in the state, and with the help of the Wisconsin Department of Natural Resources, the numbers are expected to multiply in coming years.

Because bats perform a valuable service to humankind -- they eat bugs including insects that spread West Nile virus -- the DNR works closely with businesses like Wisconsin Industrial Sand to preserve and protect the resident populations. The agency has been active here for about five years.

Bats generally hibernate from October until March or April. They like places that are cool, say 40 to 55 degrees, and humid.

Most of the bats here are big browns or little browns. The DNR experts have spotted a few others, too -- Indiana bats and eastern pipistrelles, both of which are endangered species.

It's not really possible to examine them all. The Maiden Rock sand mine is a maze of tunnels over about 30 acres. The bats live in the oldest part of the cave, an area where mining dates back to the late 1920s, Stauffer said. They're on the west side, closest to the community of Maiden Rock.

Local residents don't seem to mind them, he said. That may have something to do with the fact that you can spend an evening down by the river and not get bitten by a mosquito.

Another 50,000 or so bats live in the Bay City sand mine a few miles away, which also is owned by Wisconsin Industrial Sand. The Bay City mine was closed in 1989 and not reopened until about 1 1/2 years ago, Stauffer said.

Technology enables the DNR to get a pretty good idea how many bats there are in Maiden Rock. The agency installed directional counters to keep track of bats going in and out using the main entrance, which has bat-friendly louvered doors to keep predators out.

Similar doors are being installed now in Bay City, and directional counters are planned as a next step.

In recent months, wildlife biologists also have come and collected a sampling of Maiden Rock bats for research, Stauffer said. On the east coast, bats have been dying in droves, and they're trying to find out why.

A few weeks ago, DNR officials were in town doing a "catch and release" as they gathered data about bats' weight, size and sex as they approached hibernation.

During warmer weather, bats come and go at dusk and dawn, Stauffer said. Late summer and early fall are especially busy.

"It's mostly about feeding," he said, plus bats mate right before they hibernate. The females don't actually get pregnant until spring because of delayed fertilization.

A little brown bat can eat up to 600 mosquito-size insects in an hour. A lactating female little brown can eat her body weight -- 7 to

9 grams -- or more in a night.

Because they live in old areas of the mine that no longer are being worked, bats and people coexist well, Stauffer said.

"Bats are not afraid of people. They are not bothersome," he said.

"They do their own thing, and ignore humans."

When the occasional bat wanders into an active mining area, workers generally are startled -- but unharmed. Bats don't like being held, though. They'll bite, so biologists handling them wear gloves.

Over the past three weeks, the number of active bats has slowed considerably, while the number of furry brown clusters clinging to the mine's walls and ceilings has grown.

They nestle together, huddling for warmth, especially in the cracks and crevices that are plentiful in mine shafts created by blasting.

Speaking from the experience of nearly eight years at the Maiden Rock facility, Stauffer said he, too, has learned to live with the creature he described as "a flying mouse who spends half his life asleep.

"I'm a lot better with them now than I was as a kid," he said. "Now that I know more about them, it's much less fearsome."