Written by Janelle Wicks, FOMR Director
For a couple of years now, the Friends of Malheur National Wildlife Refuge has been taking a closer look at the bats that roost in the historic CCC-era buildings at Refuge Headquarters, using both visual emergence counts and acoustic monitoring to better understand the relative abundance of bats and a general assessment of species present. We are curious about the bats themselves, but also which structures are most important to these nocturnal residents.
During surveys conducted June 15–17, observers recorded 2,688 bat emergence observations across multiple roost locations. Because some sites were counted on more than one night, this number reflects total observations rather than a unique population estimate. To compare activity across buildings, the team used the highest count recorded at each site, resulting in a summed maximum count of 2,136 bats across the surveyed roosts.
The most active sites included the biology building, Cranes Nest Store, Visitor Center, and Pelican Place Residence, all of which showed the strongest emergence activity during the survey period. Bat Condo 1 and Bat Condo 2 showed very similar activity on June 16 and June 17, suggesting stable use of those structures. The Bat House, the largest of the habitat mitigation installations, showed no emergence activity, indicating that it is not currently being used by bats.
These numbers offer a conservative snapshot of bat use at Refuge Headquarters, not a definitive population count. Bat emergence surveys are challenging in historic buildings, especially in low light and around overhead obstructions that make it difficult to see bats clearly as they leave the structures. Nearby flight activity can also make it hard to tell whether a bat is emerging from a building or simply passing by.
In addition to the visual counts, Echo Meter acoustic surveys recorded 506 automated bat detections over the same three-day period, representing 11 probable bat taxa. Little brown myotis was the most frequently detected species, followed by California myotis, hoary bat, and Mexican free-tailed bat. Together, those four species accounted for more than three-quarters of all species-level detections and are very likely species in the area.
Other bats detected by the Echo Meter technology included western small-footed myotis, Yuma myotis, long-legged myotis, canyon bat or western pipistrelle, silver-haired bat, big brown bat, and pallid bat. A few additional species were listed as possible taxa but were not detected in this dataset.
Together, the emergence counts and acoustic surveys provide an important look at bat activity around Refuge Headquarters. They help Friends of Malheur better understand how these historic buildings are being used, and they offer a foundation for future stewardship of both the buildings and the wildlife that depend on them.
Repeat surveys will be conducted in August coinciding with the Sod House Ranch Stewardship Weekend, August 7th – 9th. If you would like to participate, please email [email protected]. Lodging will be available at the Malheur Field Station for volunteers assisting with either or both volunteer opportunity.
