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US Fish & Wildlife Service FieldNotes

Bat Monitoring at Rachel Carson National Wildlife Refuge

Region 5, October 2, 2012
A passive acoustic bat detector deployed by a tidal marsh at Rachel Carson NWR.
A passive acoustic bat detector deployed by a tidal marsh at Rachel Carson NWR. - Photo Credit: n/a

This was the first year for monitoring bats on Rachel Carson National Wildlife Refuge (NWR)! These surveys will provide a baseline inventory of bat species and habitat use on the refuge, for which we have essentially no information. Bats species populations are a growing concern for the U.S. Fish and Wildlife Service. Inventorying bat habitat use by species will permit identification of critical areas with high bat activity and locations that may be important for supporting maternal colonies. This will help the Service to direct conservation activities to locations where they will be most beneficial. Further, by monitoring trends in bat species populations we will be able to evaluate the need for, and success of, future conservation management actions.

Using special acoustic detectors with ultrasonic microphones, the echolocation calls of bats can be detected and recorded. Different bat species tend to produce different echolocation “chirps”, thus making it possible to identify the presence of different species at a site as well as evaluate relative bat activity levels in different habitat locations. Three methods of acoustic monitoring were performed this past summer at Rachel Carson NWR – passive mobile transects, passive stationary monitoring, and active monitoring. All of these bat surveys were coordinated at the regional level so data collected at the refuge is also informative at the landscape scale. Consequently, the information gained will be valuable for conservation planning and management at multiple spatial scales.

The mobile survey protocol is a standardized protocol being conducted throughout the state of Maine and numerous other states in the northeast. To implement the mobile surveys, Rachel Carson NWR employee Lindsey Fenderson used GIS to develop two 30-mile mobile acoustic bat survey routes in southeast Maine. Approximately 9.6 miles of the survey routes run adjacent to large portions of the refuge and thus these surveys likely detect bats that utilize refuge resources.

This is also the pilot year for implementing standardized active and passive bat acoustic monitoring protocols on refuges in the northeast region. Results of survey efforts and knowledge gained based on biologist experience in this pilot year will help the refuge system develop standard acoustic bat Inventory and Monitoring protocols to ensure data consistency across field stations. These data will contribute to regional FWS bat inventory and monitoring efforts while providing high-quality data for the refuge about bat species use in specific areas of the refuge. For the passive surveys, several 30-acre survey cells were in 3 general habitat types (Forested/Shrubland, Wetland/Water and Open) were randomly selected in a GIS. As many of these cells as possible were sampled by passively monitoring suitable bat habitat within the cell, to obtain a broad insight into bat species and habitat use on Rachel Carson National Wildlife Refuge. Additionally, 6 survey points in relatively close proximity that were representative of the habitats available on the refuge were identified for conducting repeated active monitoring surveys throughout the maternity season.

With the help of several seasonal interns and volunteers, Lindsey completed 3 mobile surveys on both transect routes, 10 active monitoring surveys at each of the 6 pre-selected survey locations, and deployed the passive monitoring detectors at 18 locations on the Refuge for a total of 257 survey hours. Bats of different species were successfully detected using all of these methods in all of the surveyed areas of the refuge. Additionally, several locations have been identified on the refuge as having high summer bat activity that may be important sites for maternity colonies. Approximately 2776 bat calls were collected, and although species identifications are not yet complete, preliminary analyses indicate the presence of at least eastern red bats, hoary bats, northern long-eared bats and big brown bats on Rachel Carson NWR.

Contact Info: Ward Feurt, 2076469226, ward_feurt@fws.gov