Wisconsin Bats

By Mike Reiter
Polk County Naturalist

Little Brown Bat

Earlier last month I attended a Lakes Conference in Stevens Point and heard an interesting talk entitled “Ecology of Wisconsin Bats”. Paul White, a Bat ecologist from the Bureau of Natural Heritage Conservation with Wisconsin DNR, gave a review of our local bats and the problems they face. Wisconsin is home to eight species of bats. Several of these species migrate to warmer climates for the winter while others hibernate in caves and mines. Our cave bats now face the threat of extinction from a new threat, white-nose syndrome.

According to Paul, there are 1250 species of beneficial bats worldwide. They concentrate in small areas which makes them vulnerable. These valuable animals usually have one pup per year and live a long life. Their main predators are snakes, owls, hawks, cats, raccoons and also humans. While we don’t eat bats, we can greatly influence their life style and modify their habitat. All our bats are “insectivores” which means they are insect eaters and will consume 1200 – 1500 insects per hour or their bodyweight per night. Bats also are great pollinators and seed dispensers greatly aiding the plant community. More bats on the landscape means we can get by with less pesticide. It’s a win-win for all involved.

As mentioned earlier, Wisconsin has eight species of bats. All are considered state threatened. Some are “tree bats” while others are “cave bats”. Tree bats migrate to warmer climates in the winter, while the cave bats need a specialized place to hibernate during winter months. Their hibernating numbers at one location can be as low as 10 or number in the 1000’s at times. These places need to maintain a relatively narrow range of temperature with constant humidity. There are relatively few locations for them to do this. Only about 150 locations in the state are suitable, with most located in the unglaciated area of Wisconsin and in Door County. Pierce County also has some excellent over-wintering areas. They spend 6-8 months in these locations living off their stored fat supplies.

White-nose syndrome (WNS) is a fungal disease, named for the white colored fungus growing on the face of the infected animal.  It originated in Europe and Asia and has spread to numerous states causing the death of millions of  bats. It disrupts the hibernation cycle of the bat, making it wake up and burn precious energy stored in its minimal body fat. The bat will then die of exposure. Humans can also spread the disease by the unintentional transporting it to hibernation sites. WNS was first documented in Wisconsin in the spring of 2014. Since that time it has devastated bat population in several locations of our state!

WNS has affected many species of cave-hibernating bats in the U.S. and Canada, causing declines approaching 100% in some populations. WNS poses a severe threat to all four of Wisconsin’s cave bat species: big brown bat, little brown bat, northern long-eared bat and eastern pipistrelle. WNS has been found in 2018 at all monitored sites in Wisconsin. Hopefully, there is a ray of hope, with work presently underway to develop vaccines to combat this devastating disease.

Another threat to our migrating species of bats is the electrical wind generating turbines that kill thousands of migrating bats each year. For whatever reason, the bats are drawn to these turbines and suffer huge losses.

Presently there is an ongoing effort to monitor the bats of Wisconsin using surveys, banding and implanting radio transmitters. Mist nets are used for capturing the bats unharmed. Bats can be long lived with one tagged bat recaptured after first being tagged 32 years earlier. We can also help by better understanding the life style of these interesting mammals and not fear them.

Mike’s Bat

This spring, (thankfully) my little brown bat has returned to his nightly position at our front door entrance and is taking care of any unwelcome insect pests. Despite a few bat droppings on the driveway, it is a very welcome return visitor! Put up a bat house for them and they will surely be there to help you with noxious insect control! We need to monitor and protect these unique animal species before they hit the tipping point of no return!