Acoustic amphibian monitoring, 2018: Sleeping Bear Dunes 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 Sleeping Bear Dunes National Lakeshore (SLBE) beginning 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 six species of frogs and toads at SLBE in 2018, with three species occurring at nearly every site: Gray Treefrog, Green Frog, and Spring Peeper. Eastern American Toad was found at seven sites, Wood Frog at six sites, and Northern Leopard Frog at five sites. As in prior years, including the initial inventory, there were no detections for Fowler’s Toad, Cope’s Gray Treefrog, American Bullfrog, Pickerel Frog, or Western Chorus Frog. Data collection issues in 2018 included no recorder deployment at SLBE11, no temperature log for SLBE09, and all deployed recorders failing before the target end date of 1 August, presumably due to battery drains. This issue was resolved in 2019 by replacing all aging recorders with new units. While early failures did not seem to affect occupancy conclusions, it did reduce the number of detections for late-calling species. Commission error rates (false presence) for automated detection were 0% for most species (<1.00% for Eastern American Toad and Wood Frog, and 3.67% for Spring Peeper). No commission errors enter into site occupancy statistics, as they are rejected by the proofing process. The multi-year occupancy record is highly consistent across years except for Northern Leopard Frog, which occupied several new sites in 2018. We expanded analyses and reporting in 2018 to address calling phenology and to provide a second metric 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 samples with automated detections are reported from sites across years. We also added analysis of false presence error rates for automated detection algorithms. 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: Sleeping Bear Dunes National Lakeshore

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