Acoustic amphibian monitoring, 2018: Isle Royale National Park

Casper, Gary; Nadeau, Stefanie; Kirschbaum, Al

The National Park Service Great Lakes Inventory and Monitoring Network (GLKN) established ten permanent acoustic amphibian monitoring sites at Isle Royale National Park (ISRO) in 2015. 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 six species of frogs and toads at ISRO in 2018, including the first confirmed occurrence of Gray Treefrog near Windigo. Three species were found at nearly every site: Eastern American Toad, Green Frog, and Spring Peeper. Gray Treefrog and Boreal Chorus Frog were found at only single sites each. Northern Leopard Frog and Mink Frog were not detected at 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 methodology for analyzing false presence error rates from automated detection algorithms, as a correction factor for estimating the number of samples with automated detections annually for each species. 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 in 2018 did not meet program goals for sampling early calling species due to several late deployments, however new recorders supplied in 2019 and options for fall deployments on delayed starts should resolve this issue moving forward. A recent publication on splash pools at Isle Royale National Park (Egan et al. 2015) also alerted us to additional data now available for the rare Boreal Chorus Frog. The species uses splash pool habitats along the southeastern coastal areas and appears to be more widespread than previously reported. However, we have only one monitoring site currently established in this unique habitat (ISRO10 on Passage Island). This species is not showing up in interior wetlands. We recommend considering adding one or more additional recorders to better monitor this rare species in this unique habitat, if funding can be found. Since several potential sites are very accessible near the Mott Island headquarters, deploying additional units should be fairly easy. Costs for new units are a one-time capital expense of ca. $1,000 plus ca. $350/year for data analysis. Appendices present summaries of five years of cumulative results.

Acoustic amphibian monitoring, 2018: Isle Royale National Park

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