Importance of Manually Vetting Acoustic Bat Call Files: A Case Study for Northern Long-Eared Bats

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Abstract Definitively identifying bats based on their acoustic calls is difficult and sometimes impossible. This is particularly true for Myotis species that can make similar calls, which could lead to false positive detections. This is problematic for conducting species presence or probable absence surveys using acoustic detection. Manual vetting of calls to reduce identification error by the automated programs is an option but not a requirement to survey for species listed as threatened or endangered pursuant to the Endangered Species Act. We conducted simultaneous mist net and acoustic surveys for bats in areas of Edgecombe and Johnston counties in eastern North Carolina where there are capture records of a common Myotis species, the southeastern myotis Myotis austroriparius, but not for the federally endangered northern long-eared bat Myotis septentrionalis. We caught southeastern myotis at six of the 12 sites surveyed. Although automated acoustics software produced a Maximum Likelihood Estimation value for probable presence of northern long-eared bats at three of the 12 sites surveyed, we did not catch any individuals or confirm the species acoustically through manual vetting. If we had used automated software alone without manual vetting, we would have incorrectly presumed presence of an endangered species at 25% of our sites. Therefore, manual vetting is highly recommended for northern long-eared bat acoustic surveys where southeastern myotis co-occur.