Bat Acoustic Monitoring at Fort Union Trading Post National Historic Site

A bat sleeping in a cave
Big brown bats (Eptesicus fuscus) were commonly detected at Fort Union Trading Post National Historic Site

USFWS/Ann Froschauer


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.

Acoustic recording station set up by cottonwood trees
A bat acoustic monitoring station located near some large cottonwoods adjacent to a parking lot at Fort Union Trading Post National Historic Site. This station detected the most leaf-roosting species.


Highlights (2015-2017)

  • Nine species were confirmed present or probably present in the park: big brown bats (Eptesicus fuscus), eastern red bat (Lasiurus borealis), hoary bat (Lasiurus cinereus), silver-haired bat (Lasionycteris noctivagans), western small-footed myotis (Myotis ciliolabrum), long-eared myotis (Myotis evotis), little brown bat (Myotis lucifugus), northern long-eared bat (Myotis septentrionalis), and long-legged myotis (Myotis volans).

  • Big brown bats and silver-haired bats were the most commonly recorded species, followed by little brown and hoary bats. Hear a big brown bat call!
  • Eastern red bat, hoary bat, silver-haired bat, northern long-eared bat, and long-eared myotis were new detections for the park.
  • Big brown bats and little brown bats had the highest activity near the fort structures and maintenance areas. These species are known to roost in buildings.
  • Leaf-roosting bats such as eastern red bats and silver-haired bats were more common near several large cottonwood trees that border a parking lot.
  • Bat activity is moderate compared to other network parks and may be due to an absence of large old trees. Maintaining the forested Missouri floodplain will be important for maintaining bat populations, including the threatened northern long-eared bat.
Side view of a small brown bat with long ears resting upside down from a rock
Northern long-eared bats (Myotis septentrionalis) were a new detection for Fort Union Trading Post NHS. This species is threatened and highly vulnerable to white-nose syndrome.


White-nose syndrome

White-nose syndrome is a rapidly expanding fungal disease that is spreading quickly, threatening bat populations in North America. First documented in a New York cave in 2006, this disease is associated with more than seven million bat deaths. It spreads primarily from bat to bat and humans might be spreading the disease by carrying nearly invisible fungal spores on their shoes and clothing from one cave to another.

White-nose syndrome has not yet been detected at the park, but the fungus (Pseudogymnoascus destructans) that causes it was detected in 2017 in South Dakota for the first time, a few hundred miles south of Fort Union Trading Post National Historic Site. See a map of white-nose syndrome in national parks and learn more about how you can help prevent the spread of this fungus. Continued monitoring, and park staff and visitor observations, will help us protect bat communities that live and forage in the park.

For More Information

Dan Licht, Midwest Region Wildlife Biologist
Protocol Contact: Northern Great Plains Network

Summary by Tani Hubbard, updated in 2018

Last updated: August 15, 2018