Acoustic amphibian monitoring, 2018: Pictured Rocks National Lakeshore

Casper, Gary; Nadeau, Stefanie; Kirschbaum, Al

The National Park Service Great Lakes Inventory and Monitoring Network (GLKN) established 10 permanent acoustic amphibian monitoring sites at Pictured Rocks National Lakeshore (PIRO) in 2013. Digital acoustic samples of 5-minute duration are collected by placing automated recorders with omnidirectional stereo microphones at each site. Temperature loggers co-located with the recorders collect air temperature during the sample period. The monitoring program detected five species of frogs and toads at PIRO in 2018, with Green Frog and Spring Peeper occurring at every site. Eastern American Toad and Gray Treefrog were confirmed at seven sites each, and Wood Frog at five sites. Persistence at sites across years is very consistent. Northern Leopard Frog and Mink Frog remain undetected at monitored sites but are known to occur nearby. Data collection issues in 2018 were minimal, but all recorders were deployed somewhat later than the target program date of 1 April. Additionally, minor sampling gaps occurred at PIRO10, which may be due to aging equipment (all recorders were replaced with new, more efficient units in 2019). Daily maximum temperatures exceeded the threshold of 40°F as soon as recorders were deployed in late April, so frogs had likely started calling before units were deployed. Photo documentation was also lacking and has been for several years, which compromises our ability to proof data collection issues and to track habitat changes. We expanded analyses and reporting in 2018 to address calling phenology, and to provide additional metrics for tracking changes in abundance across years. Abundance is tracked by assessing how the maximum call intensity changes on sites across years, and by how many samples with automated detections are reported across years. We also added analysis of false presence error rates for automated detection algorithms, which were <1% for all species in 2018 except Green Frog (2.21%) and Spring Peeper (10.00%). No commission errors enter into site occupancy statistics, as they are rejected by the proofing process. 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. Appendices present summaries of five years of cumulative results.

Acoustic amphibian monitoring, 2018: Pictured Rocks National Lakeshore

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