Fort Union Trading Post National Historic Site is a 440-acre park that straddles the North Dakota and Montana border. The Missouri River flows through the park and is lined by forested floodplain that provides foraging and roosting habitat for bats. Some bats can eat thousands of mosquitoes each night, making them important for insect control along the river and in the croplands that surround this park.
The Northern Great Plains Inventory & Monitoring Network monitors bats to detect long-term trends in bat populations at the park. Four acoustic recording stations were established in 2015 at Fort Union Trading Post National Historic Site: three d above the floodplain and one in the floodplain. There were 47,095 bat call recordings from stations across all survey nights from 2015–2017. The data were analyzed through specialized software programs that make preliminary identifications of the bat species based on individual call characteristics, such as a frequency and shape. Some bat species make calls that are similar to other species, which is why researchers with special expertise review the calls and make the final species determinations.