Acoustic amphibian monitoring, 2019 data summary: Pictured Rocks National Lakeshore

Abstract

Amphibians are a Vital Sign indicator for monitoring long-term ecosystem health in seven national park units that comprise the Great Lakes Network. We present here the results for 2019 amphibian monitoring at Pictured Rocks National Lakeshore (PIRO). Appendices contain tabular summaries for six years of cumulative results. The National Park Service Great Lakes Inventory and Monitoring Network established 10 permanent acoustic amphibian monitoring sites at PIRO in 2013. Acoustic samples are collected by placing automated recorders with omnidirectional stereo microphones at each of the 10 sampling sites. Temperature loggers co-located with the recorders also collect air temperature during the sampling period. We expanded analyses and reporting in 2018 to address calling phenology and to provide a second metric for tracking changes in abundance across years. Occupancy analyses track whether or not a site was occupied by a species. 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. Using two independent survey methods, manual and automated, with large sample sizes continues to return reliable results, providing a confident record of site occupancy for most species. The monitoring program detected five of the six species of frog and toad known to occur at PIRO in 2019, with Eastern American Toad, Gray Treefrog, Green Frog, and Spring Peeper occurring at almost every site sampled. Wood Frog was found at five sites. Mink Frog is known to occur at Sand Point but has never been confirmed at sites monitored by this GLKN program. Additional species of potential occurrence remain hypothetical (i.e., Northern Leopard Frog). The only significant data collection issue in 2019 was at PIRO02, where the equipment recorded only intermittently resulting in only partial data analysis possible. Remaining sites successfully collected data as programmed. Cumulative program result summaries since inception are provided in appendices. Temperature logs in 2019 showed that the threshold of ≥40°F was uniformly exceeded by 1 May, hence we recommend making 10 April the target start date for data collection in future. This could be accomplished by fall deployment of recorders on delayed starts. We also recommend making sure that recorders are mounted 6–10 feet high to better survey the soundscape with less interference from foliage, and that temperature loggers be placed within solar shields.