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Michigan dnr > wildlife viewing guide > upper peninsula > millie

7 Millie Mine Bat Viewing Site Upper Peninsula

wildlife viewing  |  directions and facility information

Little Brown Bats      Close up of Big Brown Bat
Photo: Bill Scullon, MI DNR

All bats have a sophisticated sonar system that allows them to capture flying insects in total darkness. Bats are very beneficial to humans, consuming thousands of insects, many of them considered pests, every night.

bat viewing site sign  building the bat mine cage
Bat Viewing Ssite and Buildling theBat Cage
Photo l-r: Bill Scullon, MI DNR; David Kenyon, MI DNR

The visible portion of this site is small and inconspicuous—just the mouth of an abandoned iron ore mine that is covered with a special steel grate. But what lies beneath the surface is another story. A steep mine shaft drops 360 feet into the earth, providing a roosting and hibernation chamber for bats. The mine entrance is just a short walk from the site parking area. This abandoned mine is just one of thousands that were created in the upper peninsula throughout its rich mining history. Mine shafts opened in search of iron, gold, copper, and uranium. Many mine shafts have been closed with rock, earth, even old car bodies, to reduce their hazard to humans, but unfortunately, also destroying their value to over-wintering bats. The special grate on the Millie Mine prevents people from falling into its vertical shaft, yet allows bats to come and go as they please. This is one of about 30 sites that have been protected with similar bat entrance grates in the Upper Peninsula. It is the first one to be developed as a bat interpretive site.

Wildlife Viewing

bats on cave ceiling
Bats on the cave ceiling
Photo: Bill Scullon, MI DNR

The Millie Mine is a critical hibernating and breeding location for up to 50,000 bats—one of the largest known concentrations of bats in the Midwest. Big brown and little brown bats from all over the region come here to hibernate during the cold winter months. They are believed to migrate in from throughout the Great Lakes region–Wisconsin, Minnesota, Ontario, perhaps even Michigan’s Lower Peninsula. Bats start arriving at the mine in late August and early September. They remain in the mine shaft throughout the winter and begin emerging in late April and May. Some use the mine as their permanent home. Most, however, will fly back to their forested home areas to spend the summer where they roost during the day under the bark of dead trees or in other small crevices. The females will typically use large hollow trees, abandoned buildings, or other human structures as maternity roost sites where they raise their young with other females during the summer. Males live a separate and more solitary life during this time.

bat festival - picture of announcers and bat cage
Bat festival
Photo: Bill Scullon, MI DNR

The best time to view bats is in September and early October, right at dusk, as the bats begin to emerge from the mine. They feed throughout the night and return an hour to half hour before daylight. Local businesses cooperated with the Department of Natural Resources and its Nongame Wildlife Fund to erect the steel cage over the top of this mine and to develop it as a bat interpretive site. It has become an area attraction, adding economic benefits to the Iron Mountain area. The site has been host to a national bat festival that is held annually throughout the country by Bat Conservation International. The festival attracted thousands of participants when held at this wildlife viewing site.


From the intersection of US-141 and US-2, drive west on US-2 for 1.8 miles. Turn right (north) and proceed about one mile to the parking area, which is just over the hill on the left (west) side of the street. The entrance to the cave is a short walk up the hill from the parking area.

Ownership: City of Iron Mountain (906) 774-8530

Size: 5 acres

Closest Town: Iron Mountain

Weather and Driving Directions for Iron Mountain

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