Bats in the UP

Bats in the Upper Peninsula

Canoeing by moonlight on Gratiot Lake is a special treat made all the more interesting by bats skimming the water (and occasionally the canoeist's head) as they chase after low flying insects. Bats are not only an important part of the summer evening landscape at the lake but also efficient mosquito eliminators. A little brown bat (Myotis lucifugus), the most common species in the Keweenaw, can consume up to 1,000 flying insects in an hour and over half its body weight in insects in a night.

The Keweenaw is home to seven bat species. Three Keweenaw bat species are seasonal residents who migrate: the red bat, the hoary bat, and the silver bat. Four species hibernate in caves and old mine shafts: the little brown bat, the big brown bat, the northern long- eared bat, and the tri-colored bat (formerly pipistrelle). About 90% of Michigan’s hibernating bats winter in the UP, mostly in old mines in the western UP. Some of these hibernation locations - called hibernacula - house just a few bats, some house tens of thousands.

In hibernation the bat's body temperature drops and heart beat and respiration slow. The breathing of a hibernating bat is imperceptible, and its body is cold to touch. Its heartbeat drops from roughly 400 beats per minute when awake, to about 25 in hibernation, and its body temperature drops to within a few tenths of one degree of the surrounding cave. The bat's fat stores are slowly metabolized during hibernation which can last eight months. Even a few moments of disturbance during this time can waste 30 to 60 days worth of fat reserves. 

Beneficial Bats Need Our Help

Although some folks fear that bats will swoop down and become entangled in their hair (which is folklore) or can transmit disease, the really alarming fact concerning bats is that hibernating bats are rapidly being wiped out by an aggressive fungal parasite, Geomyces destructans. This cold loving fungus is dubbed “White Nose” because it grows on bat skin membranes and forms a fuzzy white growth on their muzzles. White Nose fungus is a constant irritant that causes bats to be repeatedly roused from their hibernating torpor. Since hibernating bats don’t eat for many months, any disturbance depletes precious stored fat resources. Starving, infected bats may even leave hibernacula in mid-winter in search of food which is non-existent at that time.

Ultimately, more than 90% of bats infected by the fungus starve to death. Along the East Coast of the U.S. whole bat populations are being wiped out. Michigan now holds the distinction of being one of the last Midwest outposts with hiber- nacula free of the deadly White Nose fungus as it continues to spread west from the east coast. Experts fear this fungus may push the little brown bat, now the most common bat in the Keweenaw, to extinction in the lower 48 states in 15 years!

Because bats are very social creatures, the fungus is easily transmitted from bat to bat. White Nose fungus is a disease specific to bats and not harmful to people or other animals. However, the fungus can travel on the clothing, shoes, and equipment of people who visit or work in caves and mines, and can also be transmitted to bats in this way. So there is an effort nationally to find and implement ways to stem the transmission of the disease by people to these extremely beneficial bats.

Bill Scullon, MDNR wildlife biologist, Dr. Allen Kurta of Eastern Michigan University, and caver Steve Smith are surveying Michigan hibernacula. Currently, they monitor about 60 sites in the western U.P. Scullon indicated that the MDNR is educating cave enthusiasts, rockhounds, and owners of caves and mines open to tourism on methods to help protect bats from exposure to the fungus. Some caves and mines have already been gated to allow entry to bats but to exclude entry to people either year round or during hibernation times. There are a number of these gates in Houghton and Keweenaw Counties. Seneca #3 shaft in Mohawk (pictured at right) and the Pewabic shaft associated with Quincy mine are examples of bat enclosures or bat gates. Cavers and rock- hounds are being informed about decontamination procedures to use when going from site to site, and about the importance of not entering hibernacula in fall and winter. The DNR works with owners of sites which are open to tourism, such as Quincy and Delaware Mines, to help reduce the likelihood that the fungus could be brought in by visitors.

Many thanks to Bill Scullon, the MDNR wildlife biologist in charge of bat monitoring, for providing some of the information in this article! If you find large numbers of dead/dying bats (especially near mine entrances) or flying bats out-of-doors during hibernation times, or find bats with white fuzz on their muzzles, please report this to Bill Scullon at 906-563-9727 or

If Bats Become A Nuisance

Although they seldom carry rabies or other diseases harmful to humans, bats sometimes become unwanted house guests. If bats must be evicted from your home please consider timing and method. 

Rather than trying to trap or poison bats (which is illegal), exclude them by patching holes when they have left your home for winter hibernation elsewhere. 

Bat Conservation International also has information on constructing bat exclosure tubes and sheeting. These devices function as one way valves that allow bats to exit but not to reenter home roosts after the breeding season.

Reasons to be Grateful for Bats

A little brown bat can consume over 1000 mosquitoes and blackflies a night! That means a lot less swatting for us.

Bats are considered major predators of agricultural and forest insect pests. A bat eats nearly its body weight in insects every night during its active season. Because of the insect control services that bats offer, both crop damage and the need for pesticides are reduced, saving Michigan farmers an estimated $5,000,000. per year! Using less pesticide is also an environmental benefit.

The acrobatics of these graceful and mysterious nighttime creatures are fun to watch.

What would Halloween be without bats?

Don’t bats transmit diseases to humans?

The incidence of rabies in bats tested in the wild is only 1%, much less than raccoons for instance. However, among animals found dead (or killed after biting humans), bats top the list of those testing positive for rabies. That said, it is a rare occurrence for people to contract rabies from a bat. Experts I spoke to could not recall any such cases reported in the U.P. However, persons have received prophylactic treatment for rabies after exposure to bats testing positive for rabies.

If a bat enters your home, the best policy is to open windows and doors to allow its exit. Never pick up a bat with your bare hands. Instructions for safe bat removal are available on the web at the bat conservation organization websites. If a dead bat is lying on the ground, wear gloves or scoop it up in a container for disposal. Never handle a bat with bare hands.

When not hibernating, females seek sheltered environments to raise their young. They can enter homes through holes in the soffit, eaves, or chimney. If you can put your thumb in the hole, it is large enough for a bat to enter! Never relocate bats between early May and late August (in the Keweenaw) when their babies are nursing and unattended while the females hunt at night. If bats have moved into your attic or inside your walls to raise their young and have become a nuisance, you can block their re-entry after they have vacated for the winter. According to Bill Scullon, bats have moved into hibernacula in the U.P. by early November. When remov- ing old bat droppings from inside buildings, experts advise the use a respirator and wetting down the droppings prior to removal in order to eliminate the possibility of contract- ing a respiratory infection called histoplasmosis. The old droppings of birds and bats may contain histoplasmosis spores which if stirred up and inhaled can lead to infection.

After blocking bat entry to your home, consider erecting a bat house nearby as a substitute accommodation. These can be mounted on poles, tree trunks, or the sides of buildings. Bat houses are available locally at hardware stores. Free bat house plans are on the Organization for Bat Conservation website.

For more on bats...

Organization for Bat Conservation

Bat Conservation International

U.S. Fish and Wildlife Service website

A first hand account of a visit to a hibirnaculum with bat monitoring team Allen Kurta and Steve Smith is featured in the October 2012 edition of Traverse, Northern Michigan’s Magazine. The informative article, “Michigan Bat Doctor Fights for the Hibernacula’s Future,” by Finlandia professor Suzanne Van Dam describes her visit to the iron mine in Vulcan, MI. 
Also available on the MyNorth website

Another great article on U.P. bats by Van Dam is in the Summer 2012 edition of the UP Environment Newsletter.