Acoustic amphibian monitoring, 2018: Grand Portage National Monument

Casper, Gary; Nadeau, Stefanie; Kirschbaum, Al

The National Park Service Great Lakes Inventory and Monitoring Network (GLKN) established six permanent acoustic amphibian monitoring sites at Grand Portage National Monument (GRPO) in 2015. Digital acoustic samples of 5-minute duration are collected by placing automated recorders with omnidirectional stereo microphones at each of the six sites. Temperature loggers co-located with the recorders collect air temperature during the sample period. Five species of frogs and toads were detected in 2018, with Eastern American Toad, Green Frog, and Spring Peeper occurring at most sites. Gray Treefrog and Wood Frog were each found at three sites in 2018. Mink Frog, Northern Leopard Frog, and Boreal Chorus Frog are known to occur near or within the park, but none were not detected at any monitored sites in 2018. We expanded analyses and reporting in 2018 to address calling phenology, and to provide additional metrics for tracking changes in abundance (in addition to occupancy) across years. Abundance is tracked by assessing how the maximum call intensity changes on sites across years, and by how many automated detections are reported from sites across years. We also added analysis of false presence error rates for automated detection algorithms, which were less than 3% in 2018. The dual survey approach with large sample sizes continues to return reliable results, providing a near-perfect record of site occupancy for most species. False absences are accounted for in periodic occupancy modeling. False positives for site occupancy are eliminated by dual-observer proofing. Data collection issues in 2018 were minimal; sampling did start somewhat late in the season, but this did not appear to reduce site level detection of early calling species. Appendices present summaries of four years of cumulative results.

Acoustic amphibian monitoring, 2018: Grand Portage National Monument

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