Acoustic amphibian monitoring, 2019 data summary: Isle Royale National Park

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 Isle Royale National Park (ISRO). 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 ISRO in 2015. 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. The monitoring program detected all seven species of frog and toad known to occur at ISRO in 2019, with Eastern American Toad, Green Frog and Spring Peeper occurring at almost every site sampled, and Wood Frog at six sites. Gray Treefrog, Mink Frog, and Boreal Chorus Frog were found at only one or two sites each. Northern Leopard Frog has yet to be confirmed at ISRO in this GLKN monitoring program. We expanded analyses and reporting in 2018 to address calling phenology and to provide a second metric for tracking changes in abundance (as opposed to occupancy) 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. There were no significant data collection issues in 2019. Three units stopped collecting data early but these data gaps did not compromise sampling rigor or analysis. Since temperature logs show that the threshold of ≥40°F was often exceeded by 1 April in 2019, making 15 March a start date for data collection may be considered if park personnel feel snow and ice cover would be reduced enough by that date as well. We do recommend making sure that temperature logger solar shields in future are not hanging in such a manner as to be banging against anything in a breeze, as this contaminates the soundscape