Acoustic Bat Monitoring

Bats are nocturnal mammals that dwell in caves, trees, mines and rock crevices. These animals are the second largest order of mammals (Chiroptera) with more than 1,200 species worldwide. Specifically, Illinois has 13 species of bats, four of which are state-listed endangered, two are state-listed threatened, and six of which are on the IWAP Watch List due to concerns about their conservation status. 

Illinois bats are insectivores (consume insects) and play a crucial role in our ecosystem as they support cave communities, aid in pest consumption and act as prey for other organisms. Tara Hohoff, a scientist with the Illinois Bat Conservation Program (IBCP), states there are “misconceptions about the types of bats we have in Illinois,” as people commonly think Illinois is home to fruit-eating and pollinating bats. Sadly, bats face local and worldwide declines due to white-nose syndrome (a wildlife disease), destruction of habitat and climate change.

According to Joe Kath, Illinois Department of Natural Resources (IDNR) endangered species program manager, white-nose syndrome (WNS) is an emerging wildlife disease in North American bats which has resulted in the dramatic decrease of the bat population throughout the United States and Canada, literally killing millions of bats.

The disease is caused by the fungus Pseudogymnoascus destructans, which colonizes the bat’s skin. The condition is named for a distinctive fungal growth around the muzzles and on the wings of hibernating bats. WNS was first identified in February 2006 in upstate New York. Since then, it has spread across North America and Canada. As of 2021, WNS has been identified in 35 states and seven Canadian provinces. Existing as far as Washington state, Kath said “Essentially WNS spans North America from the east coast all the way to the west coast.”

WNS was first discovered in Illinois by Kath in 2013. As of 2021, WNS has been documented in 14 Illinois counties.

It is estimated that WNS has killed 6.7 million bats in North America since its discovery in 2006. At some sites, greater than 95 percent of bats have died due solely to WNS. Driven by WNS, the U.S. Fish and Wildlife Service (USFWS) recently initiated a three bat Species Status Assessment or SSA. The three species included in the SSA are the little brown bat, tri-colored bat and northern long-eared bat, primarily because these are the species currently being impacted the most by WNS. The IDNR’s endangered species program is participating in this SSA. According to Kath, the SSA framework is an analytical approach developed by the USFWS to deliver foundational science for informing all decisions under the Federal Endangered Species Act (ESA).

“Essentially, an SSA is a biological risk assessment to aid decision makers who must use the best available scientific information to make policy decisions under the ESA,” Kath explained. “The SSA does not result in a decision directly, but it provides the best available scientific information to guide ESA decisions.” Results of this SSA should be available within the next six months.

With bats facing so many threats, studying them with use of modern technology is needed now more than ever. Many bat species worldwide, including all 13 species in Illinois, use echolocation, which is the production of soundwaves that bounce off objects in the environment and are sent back to the bat’s ears, allowing them to identify objects in their flight path. Bats use both echolocation and their vision, to navigate and forage and escape threats, such as wind-turbines and predators. Echolocation is not only useful for bats, but also for researchers. Researchers can record and study acoustic data from the soundwaves produced by echolocating bats to give insight on many aspects of their lives. This is known as acoustic monitoring. Echolocation call sequences (multiple call pulses in succession) can be detected using specialized acoustic recorders and that are then analyzed by researchers using unique software. This survey method allows researchers to monitor general behavior, habitat selection, distribution and community structure. Raw acoustic data can be used to identity phonic groups (also known as “sonotypes”) unique to each species. Each species’ call pulses have specific measurable variables such as frequency, slope and duration that allow researchers to identify them. However, species identification is only achieved if recorded calls are relatively free of background noise and the animal is close enough to the device for a quality recording. Basic acoustic monitoring techniques tell us what species are present. More advanced techniques offer information about how bats are communicating with each other as well as changes in bat abundance and bat activity across the landscape.

Acoustic monitoring much minimal effort in the field and devices are programmed to record for long periods of time, often yielding more data than methods such as mist netting. Acoustic monitoring is valuable for bat conservation, however, there are limitations. For example, identification of certain species and distinguishing a bat’s age and sex may not be attainable in some cases.

Hohoff commented on acoustic monitoring limitations: “There are still some species of bats that are difficult to differentiate with acoustics, particularly the Myotis species. Most of these species have been hard hit by white-nose syndrome so I would argue that knowing exactly which species it is is less important sometimes than knowing that Myotis are present.” This indicates that despite limitations with this technology these efforts still yield useful information.

Bat species around the globe are on a rapid decline, however, acoustic monitoring can aid in conservation and management efforts for these mammals. Acoustic monitoring and other bat conservation efforts throughout Illinois are being conducted by the Illinois Bat Conservation Program (IBCP) in conjunction with the IDNR. Current research is focused on understanding bat species distribution and monitoring long-term population trends. DNA analysis of bat guano is used to identify which bat species are using roosts without physically handling the animals, as well as determining what the bats are eating. Funding for these projects are provided by the IDNR Divisions of Wildlife and Natural Heritage.

Nationally, the North American Bat Monitoring Program (NABat) works to provide reliable data and monitoring protocol to promote effective conservation decisions for bat populations, as well as inform policymakers regarding impacts on bat species. NABat uses predetermined 10 X 10 km grid cells to prioritize and rank monitoring efforts known as GRTS (Generalized Random Stratified survey). Each GRTS is divided into four quadrants with two to four ultrasonic recorders placed among the four quadrants. This monitoring design is implemented by NABat, but acoustic routes in Illinois are run annually by the IBCP and IDNR. The efforts of the IBCP and IDNR help contribute to the broader goal of monitoring and preserving bat populations.

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Isabella Newingham is the new State Wildlife Action Plan and Aquatic Ecology GPSI intern at the Illinois Department of Natural Resources. She graduated with a bachelor’s degree in Biology from Millikin University in 2020. She spent the year following graduation teaching at a local high school before starting at the University of Illinois Springfield to complete a master’s degree in Environmental Sciences with a concentration in Sustainable Development and Policy. While at Millikin University she completed research to observe behavioral responses in millipedes.