Methods to Inventory and Monitor Forest Bats

Research Issue

Methods to inventory and monitor wildlife are critical for effective management. Managers need to know what species inhabit their properties as well as determine the status and trends of populations under various management regimes over time. Monitoring methods are also necessary for determining which species are at risk of extinction. There are many unknowns related to effective inventory and monitoring of bat populations including the types of survey methods that should be employed, the time and frequency of surveys, sample sizes, and factors that affect variation in counts or indices. Research is needed to develop and test various inventory and monitoring methods to provide managers with the most effective and efficient protocols.

Our Research

We have conducted a variety of studies to test survey and monitoring techniques for bats. In cooperation with Clemson University and South Carolina Department of Natural Resources, we tested whether bridge surveys were an effective method for determining the distribution of Rafinesque’s bats across large geographic areas. We also determined the number of surveys that are needed to ensure that bats are detected.

Image of Bat Detector

A bat detector.

Bat detectors are a common method for surveying and monitoring bats across the landscape. However, there are many factors that can affect the results of acoustical surveys using bat detectors in the field. We tested the effects of several types of microphone weather-proofing that are commonly used and found that the type of weather-proofing used can have a large impact on the quantity and quality of bat calls recorded which can greatly impact survey results. We are also determining the number of nights of sampling necessary to detect five bat species in Kentucky.

Image of Rafinesque’s big-eared bat

Rafinesque’s big-eared bat

Some species, such as Rafinesque’s big-eared bats are very difficult to capture in mist nets and are rarely recorded by bat detectors because they have very quiet echolocation calls. We tested whether we could attract Rafinesque’s big-eared bats to our mist nets by broadcasting their social calls, a method that has been used for a similar bat species in Europe. Although the method was not successful for Rafinesque’s big-eared bats, we believe it may be successful for other species and plan to test it further.

In addition to appropriate monitoring methodologies, a monitoring program must also be based on a statistically robust and logistically feasible sampling regime that will ensure that the data can be used to detect changes in the status and trends of populations. Such a sampling frame is not available for North American bats but is its development is crucial so that biologists can monitor the long-term impacts of White-nose Syndrome, climate change, energy development, and land-use change. We are currently working with many partners in other agencies to develop such a framework.

Image of Mobile Anabat

Mobile Anabat.

Expected Outcomes

Our research will provide managers with methods and protocols that can be used to effectively and efficiently inventory and monitor bat populations to determine the effects of their management actions and determine which species are at greatest risk of extinction.

Research Results

  • Britzke, E. R., B. A. Slack, M. P. Armstrong, and S. C. Loeb. 2010. Effects of orientation and weatherproofing on the detection of bat echolocation calls. Journal of Fish and Wildlife Management 1:136-141.
  • Loeb, S. C., and E. R. Britzke. 2010. Intra- and interspecific responses to Rafinesque's big-eared bat (Corynorhinus rafinesquii) social calls. Acta Chiropterologica 12:329-336.
  • Bennett, F. M., S. C. Loeb, M. S. Bunch, and W. W. Bowerman. 2008. Use and selection of bridges as day roosts by Rafinesque’s big-eared bats. American Midland Naturalist 160:386-399.

Research Principal Investigators

  • Susan C. Loeb, Southern Research Station, RWU-4157
  • Eric R. Britzke, U.S. Army Engineer Research and Development Center

Research Partners and Collaborators

  • Brooke A. Hines, Kentucky Department of Fish and Wildlife Resources
  • Michael P. Armstrong, U.S. Fish and Wildlife Service
  • Mary Bunch, South Carolina Department of Natural Resources
  • U.S. Forest Service, Savannah River Site