Development of a Bat Guano and Acoustic Sampling Testing Protocol to Identify Species Occupying Virginia Department of Transportation Bridges

Over half of Virginia’s extant bat species, including six imperiled bat species, have been documented as using bridges as day or night roosts. To prevent or minimize harm to these species, the Virginia Department of Transportation (VDOT) performs surveys to detect bat use in transportation structures when essential infrastructure maintenance must occur. The current indicators used by VDOT to inspect bridges for bat use include staining, guano piles, and the presence of live bats. Notwithstanding, without trained personnel, it can be difficult to positively identify species use. Without the ability to confidently identify roosting species, regulatory agencies cannot discount transportation structure use by a sensitive species, such as the federally endangered gray bat (Myotis grisescens). Most acoustic detection survey methods allow for the identification of bat species active in an area but cannot confirm that a species is using a transportation structure as a day or night roost with certainty. Because acoustic detection methods are relatively inexpensive and not labor intensive, they can be used to monitor areas for an extended period to determine the likelihood of bat presence and provide region-wide predictive modeling to assess potential risk. However, acoustic monitoring alone cannot confirm roost use, so a subsequent, genetics-based approach could confirm which species have roosted in a structure. In this project, the authors tested a combined approach using intensive acoustics in conjunction with DNA barcoding of guano found at the sampled bridges to detect the species present in the areas around 40 bridges in southwestern Virginia’s Bristol District. From March to November 2019, the authors observed bat activity with acoustic sampling throughout the Clinch, Powell, Holston, Big Sandy, and New River watersheds. Gray bat activity at the bridges was correlated with proximity to the known summer maternity roost in the Bristol area and mean cave density in the surrounding landscape. Combined with pilot acoustic data from 2018 and a partial continuation in 2020, the authors observed high year-to-year variations in gray bat activity. They found that a long acoustic sampling duration is necessary to discern the monthly presence and relative abundance patterns of imperiled bat species (focusing on the six imperiled species documented as using bridges) across the year from emergence to the initiation of hibernation. The spatiotemporal patterns that the authors observed can help VDOT assess the risk to gray bats and other bat species from transportation structure management activities. In total, 283 guano samples were collected from 29 bridges for subsequent DNA analysis. Although 245 of the samples were amplified, only 77 (27% of the collected samples) were of sufficient quality to find a species match. Nine bridges had guano with DNA that matched big brown bats (Eptesicus fuscus), 12 bridges had guano matching gray bats, and three bridges had guano matching the federally threatened northern long-eared bat (Myotis septentrionalis). The bat species at all the sites with guano-derived DNA were also recorded acoustically. For guano DNA analysis, additional work-refining techniques will be needed; however, as proof of concept, the combined approach to bat sampling that the authors developed may aid VDOT managers in assessing bat use of bridges, which is particularly valuable in areas such as the New River drainage into which the gray bat population is newly expanding.

• Record URL:
  https://www.virginiadot.org/vtrc/main/online_reports/pdf/22-R20.pdf
• Record URL:
  https://rosap.ntl.bts.gov/view/dot/61053
• Supplemental Notes:
  • Alternate title: Development of a Bat Guano and Acoustic Sampling Testing Protocol to Identify Species Occupying VDOT Bridges.
• Corporate Authors:

  Virginia Polytechnic Institute and State University, Blacksburg

  Department of Fish and Wildlife Conservation
  Blacksburg, VA  United States  24061

  Virginia Transportation Research Council

  530 Edgemont Road
  Charlottesville, VA  United States  22903

  Virginia Department of Transportation

  1401 East Broad Street
  Richmond, VA  United States  23219

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Taylor, Hila
  • Powers, Karen E
  • Hallerman, Eric M
• Publication Date: 2022-1

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Final Report
• Features: Appendices; Figures; Photos; References; Tables;
• Pagination: 66p

Subject/Index Terms

• TRT Terms: Acoustic detectors; Detection and identification; Endangered species; Highway bridges
• Geographic Terms: Virginia
• Subject Areas: Bridges and other structures; Environment; Highways;

Filing Info

• Accession Number: 01832580
• Record Type: Publication
• Report/Paper Numbers: FHWA/VTRC 22-R20, VTRC 22-R20
• Contract Numbers: 114417
• Files: NTL, TRIS, ATRI, USDOT, STATEDOT
• Created Date: Jan 15 2022 6:32PM