Working against time and the inevitable spread of a disease threatening bat populations across the country, Seattle District personnel are conducting wildlife surveys to determine which species live on Corps lands and if they are healthy.
Although the Corps regularly conducts wildlife surveys on its lands to help inform wildlife management decisions, recent bat surveys have additional relevance because the spread of Pseudogymnoascus destructans, a fungus that causes white-nose syndrome, a fatal disease that has devastated bat populations in the U.S. and Canada.
Since first documented in 2006, the disease has mostly impacted states east of the Rockies, but that changed in 2016 when the first case was confirmed in Washington State.
“It’s not a matter of if the disease will spread to our areas, but when,” said Rhonda Lucas, a terrestrial wildlife biologist for Seattle District, U.S. Army Corps of Engineers. “It’s important that we establish baseline information such as what species we have, where and whether or not they’ve been exposed.”
While bats have been historically demonized in movies, folk tales and popular culture, Lucas says they are vital parts of the ecosystems where they live.
The winged mammals serve as plant pollinators in some areas of the country and bat guano is considered excellent fertilizer, but the biggest benefit bats provide in the Pacific Northwest is pest control. In a single evening these nocturnal predators can consume twice their body weight in insects, helping agricultural crops by eating pests and constraining the spread of insect-borne disease.
Since bats use echolocation calls and sonar to hunt, Lucas enlisted the help of natural resource staff to help install specialized recording equipment at district operating projects. These highly-sensitive acoustic monitors record ultrasonic bat calls that are beyond the range of human hearing.
The recordings are then processed through ultrasonic signal analysis software which isolates bat calls from other extraneous sounds, such as those from insects, and produces a graphic illustration of what the calls look like and at what frequency. Armed with this information, Lucas is able to determine which calls correspond to a particular bat species.
In addition to passive monitoring, Lucas worked with members of the Engineer Research and Development Center from Vicksburg, Mississippi, to capture and test bats for white-nose syndrome at Libby Dam in 2017.
“The bats at Libby Dam represent the district’s only known breeding colony,” Lucas said. “So we set up nets to capture some which we measured and swabbed, and then sent materials off for lab testing. Thankfully all of our Libby bats came up negative so we didn’t have to worry about if the colony had been exposed.”
Thus far Lucas has conducted bat surveys at four of the district’s six operating projects and has identified 11 distinct bat species residing on Corps lands. As reports are completed, results are uploaded to a national bat database run by the U.S. Fish and Wildlife service.
“This could be one of the biggest extinction events we’ve known in modern time,” Lucas said. “So while there are currently no known treatments, we need to be proactive and gather information on the bats we have and continue monitoring them until best practices or decontamination protocols are developed.”