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Wild Side: Homeland security air force in peril

A flying little brown bat needs to eat about half its body weight in insects each night that it is active. (New Mexico Department of Natural Resources photo.)

A bat flew by my nose as I was sitting on the patio last evening. The swooshing flutter startled me from my book. Bats were flying laps around our valley, eating their way through clouds of insects as the sun started to go down. It was a pleasant evening and we weren’t bothered by mosquitoes.

The rough board-on-board siding on our shop building has become a giant bat house. Bats disperse from their winter hibernation caves in May to give birth, raise their young and to forage. Big brown, little brown, and northern pipistrelle bat females form summer nursery colonies in hot attics or barns. Other bat species can be found in summer roosting under the siding of buildings, under tree bark, under bridges or in rock crevices.

Wisconsin bats are small aerial acrobats that eat insects. Seven species of bats occur in our state; little brown bat, northern myotis, big brown bat, silver-haired bat, red bat, hoary bat, and eastern pipistrelle.

There are about 1,000 species of bats worldwide, comprising about one fifth of all mammal species. Most are small insect-eating “micro-bats.” There are about 167 species of larger fruit-eating bats, including the flying foxes of Indonesia that have wingspans of up to six feet.

Wisconsin’s small bats live on the thin edge of existence but individuals can live to be 20 years old. Their thin finger bones and the skin between them form their wings. Their lower skeletons are much reduced to save weight. This is part of the reason why bats hang upside down. Bats can’t sit in an upright roosting position like birds. Their femurs are rotated so their knees point backwards, an adaptation to hanging from their feet.

Although they are not very heavy it takes a lot of energy to fly. A little brown bat needs to eat about half its body weight in insects each night that it is active.

Crystal Cave in Spring Valley is a winter hibernaculum (hibernating site) for bats.  Owner Eric McMaster hosts Wisconsin DNR biologists doing research on the bats wintering in the cave. Last winter, about 700 bats were hibernating in Crystal Cave. McMaster said some bats are already starting to check out their winter hangout.

Crystal Cave is a remarkably large and fascinating geological feature. It’s a great place to visit to get a lesson in local geology.

North American bats are threatened by a fungal disease called “white nose syndrome.” Originating in Europe, the disease was first noticed in the eastern U.S. in 2007 and has caused devastating population declines in insect-eating bats at their hibernating sites.

The white nose syndrome fungus was detected this year on bats at the Soudan Underground Mine State Park in northern Minnesota and the Forestville/Mystery Cave State Park near Rochester. The disease is readily transmitted between bats.

White-nose syndrome causes bats to awaken during hibernation and use up energy reserves needed to get them through the winter. Hopefully, bats in our region may develop a resistance to the disease like bat populations in the northeastern United States appear to be doing.

Bats are exquisitely adapted to preying on flying insects. Bats emit high frequency sound (20 to 100 kHz, that we can’t hear) and have large ears that enable them to navigate and detect insects by sonar. The sounds they make bounce off fixed objects and insects back into the bat’s ears, get translated into nerve signals to their brains, which process the signals back to their muscles to determine a flight path and maneuvering to capture insects.

Bats prey on insects by scooping them up with their tails and then eating them.  Bats aren’t blind but they mostly rely on echolocation for feeding and flying.

Because we have bats around we have fewer mosquitoes. We feel a bit safer because bats eat the mosquitoes that carry West Nile virus. Moth-eating bats protect our gardens and our neighbors’ crops from costly infestations of rootworms.

We enjoy watching the bats and the dragonflies of our Homeland Security Air Force and appreciate their good work.  We hope that the bats survive the peril imposed by the white nose syndrome disease.

Please send any comments and suggestions for this column to me at

--Dan Wilcox, Outdoor Columnist