Bat Monitoring at Pictured Rocks National Lakeshore, 2015–2018

Bats across the country are struggling against climate change, habitat loss, wind turbines and a devastating fungal disease, white-nose syndrome.

Of the seven bat species found at Pictured Rocks National Lakeshore, three are summer visitors that winter in the southwestern United States, Mexico or even Central America. The other four stay and hibernate in caves or buildings. Three of those — the little brown, northern long-eared and tricolored bats — are highly susceptible to white-nose syndrome; the fourth, the big brown bat, has shown resistance to it.

Before monitoring

There are no records of bats at the park itself before 2003, though an early report on the area's wildlife listed six species in the region. Surveys in 2003–2004 captured and recorded little brown, northern long-eared and eastern red bats, and recorded the calls of big brown, hoary and silver-haired bats.

The park began monitoring bats by sound in 2015, as the Great Lakes Inventory and Monitoring Network started surveys in its eight other parks; the park's recordings were analysed by the network along with theirs.

Listening in

In flight, bats call to find their way and to locate food. As with birdsong, species can be told apart by their calls, but these are ultrasonic — too high for human ears — so special microphones and software record and identify them. Some species sound alike, and calls vary within a species, so the software is not 100 percent accurate; a share of the recordings are therefore checked by hand on a spectrogram.

Seven species — more or less

All six species known before were confirmed: big brown, eastern red, hoary, silver-haired, little brown and northern long-eared bats. All but the northern long-eared bat were confirmed by checking recordings by hand; that species' presence has been confirmed separately by capture in mist nets.

The tricolored bat has never been caught in the park. The park lies just north of its known range, but four hand-checked recordings from one site suggest it may be there. In 2015, acoustic surveys in the nearby Hiawatha National Forest recorded tricolored bats about 20 miles south of the lakeshore, and they have been found hibernating in mines in Michigan's Upper Peninsula. Its status in the park is still uncertain.

A tricolored bat. The park is just north of the species' range, and none has been caught there, but recordings suggest it is present. NPS photo.

All seven species were recorded every year. Silver-haired, hoary and little brown bats were recorded most often — but little brown bats fell to under 5 percent of all recordings in 2017 and 2018. Four species were heard at 70 percent or more of the sampling sites; none was recorded at every site.

Activity of hoary and silver-haired bats appears stable. Activity of big brown, eastern red, little brown and northern long-eared bats is trending down.

What comes next

The monitoring programme is working with the NABat Midwest Bat Hub on statistical models of bat occupancy — the probability that a species is using an area, allowing for the fact that it will not always be detected — especially for the species hit hardest by white-nose syndrome.

When the project began, the Great Lakes region was at the leading edge of the disease's spread, and the monitoring gave parks a baseline for their bat populations and a way to track change. In 2022 the network handed bat monitoring over to the parks, and any further monitoring at Pictured Rocks will be done by park biologists.

Sources

• National Park Service, Great Lakes Inventory and Monitoring Network, "Bat Monitoring at Pictured Rocks, 2015–2018." https://www.nps.gov/articles/000/bat-monitoring-at-pictured-rocks-2015-2018.htm
• K. R. Goodwin and A. A. Kirschbaum, Acoustic monitoring for bats at Pictured Rocks National Lakeshore: Data summary report for 2015–2018, Natural Resource Data Series NPS/GLKN/NRDS—2023/1397, 2023. https://irma.nps.gov/DataStore/DownloadFile/691149