Bat Monitoring at Sleeping Bear Dunes National Lakeshore, 2015–2019

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

Three of the bat species at Sleeping Bear Dunes National Lakeshore are summer visitors that winter in the southwestern United States, Mexico or even Central America. The rest 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 big brown bat also hibernates but has shown resistance to it.

What was known before

Five species had been recorded at the park before formal monitoring began in 2015.

• 1960s–1970s: wildlife surveys found little brown and eastern red bats on North Manitou Island, and eastern red, big brown, hoary and silver-haired bats on South Manitou.
• 2000–2002 and 2015: mist-netting in 2000 caught only big brown, eastern red and little brown bats; the same three were caught in 2001, 2002 and 2015, along with silver-haired and hoary bats. Roost surveys in 2000 found several little brown bat colonies in park buildings.
• 2010: sound recordings from a study of bird and bat migration along Great Lakes shores picked up little brown and red bats and the big brown/silver-haired pair, whose calls cannot always be told apart.

The park lies within the known range of the northern long-eared and tricolored bats and near the edge of the Indiana bat's, but none of the three had been caught or otherwise identified there. A 2014 habitat assessment found high-quality feeding and roosting habitat for Indiana and northern long-eared bats in parts of the park, and records from nearby show the species are in the area for at least part of the year. A northern long-eared bat was recorded during fall migration at Leelanau State Park, about 30 miles away, and all three have been seen hibernating at Tippy Dam, less than 50 miles from the park — though where those bats spend the summer is unknown.

Does the Indiana bat fly over Sleeping Bear Dunes? It is not yet known. USFWS photo by R. Hagerty.

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.

Spectrograms used to check bat calls by hand when the software cannot identify them, or its identification is doubtful. They show a call's frequency (in kilohertz, left) and duration (in milliseconds, bottom). NPS.

What five years found

The five species already known were confirmed: big brown, eastern red, hoary, silver-haired and little brown bats. Two more were documented for the first time: the northern long-eared bat and the tricolored bat. The software identified some recordings as Indiana bats, but checking by hand did not confirm the species.

Little brown, eastern red, big brown and silver-haired bats were each among the three most often recorded species in at least two of the years. Activity of big brown, hoary and silver-haired bats appears stable; activity of eastern red, little brown, Indiana, northern long-eared and tricolored bats showed declining trends.

The article says recordings of all eight species were captured every year, while also saying the Indiana bat was not confirmed; this page lists the Indiana bat as unconfirmed.

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 and a way to track change. In 2022 the Great Lakes Network handed bat monitoring over to the parks, so any further monitoring at Sleeping Bear Dunes will be done by park biologists.

Sources

• National Park Service, Great Lakes Inventory and Monitoring Network, "Bat Monitoring at Sleeping Bear Dunes, 2015–2019." https://www.nps.gov/articles/000/bat-monitoring-at-sleeping-bear-dunes-2015-2019.htm
• K. R. Goodwin and A. A. Kirschbaum, Acoustic monitoring for bats at Sleeping Bear Dunes National Lakeshore: Data summary report for 2015–2019, Natural Resource Data Series NPS/GLKN/NRDS—2021/1323, 2021. https://irma.nps.gov/DataStore/DownloadFile/663262