Among amphibians, frogs and toads are special: each species makes its own distinctive, identifiable call. That means their populations can be monitored by remote recorders — "frog loggers."
Monitoring matters because amphibian declines are among the most prominent conservation problems in the world. Most amphibians need both land and water in their lives, so they're sensitive to changes in temperature, rain and humidity — which makes them good indicators of climate and habitat change.
Six species
| Common name | Scientific name |
|---|---|
| Eastern American toad | Anaxyrus americanus americanus |
| Gray treefrog | Hyla versicolor |
| Green frog | Lithobates clamitans |
| Mink frog | Lithobates septentrionalis |
| Spring peeper | Pseudacris crucifer |
| Wood frog | Lithobates sylvaticus |
Frog loggers
Ten permanent monitoring sites were set up in 2013. From April, the recorder at each site takes a 5-minute sample every hour from 5 p.m. to 3 a.m., plus four extra samples on the half hour between 7:30 and 10:30 p.m. A sensor logs the temperature every hour.
A frog logger. Microphones stick out of the top left and right of the box; a temperature logger hangs under the "roof." NPS
The recordings reveal:
| Measure | What it tells |
|---|---|
| Occupancy | whether a species is present at a site |
| Abundance | tracked from how the loudest calling at each site, and how often a species is heard, change from year to year |
| Phenology | since 2018, the date each species first calls each year — for now only for three species common to all the network's parks: American toads, green frogs and treefrogs (gray treefrogs and Cope's gray treefrogs sound so alike, even on recordings, that they're counted together) |
Call Index Values
A subsample of recordings is scored for each species with a Call Index Value (CIV) — the peak intensity of calling:
| CIV | Sounds like |
|---|---|
| 1 | separate calls with silence between — few singing males, which can be counted |
| 2 | in between |
| 3 | a full chorus: calls constant, continuous and overlapping, too many to count |
Tracked over the years, CIVs show whether a species is increasing or decreasing.
2019 results
- Five of the six species were recorded. American toads, gray treefrogs, green frogs and spring peepers turned up at almost every site.
- The mink frog is known at Sand Point but has never been heard at a monitoring site.
- First calls: American toads in mid-May, then gray treefrogs in late May, then green frogs on June 1.
- Every species reached CIV 3 at one site or more — except the wood frog, which peaked at CIV 2 at two of the five sites where it was heard. Spring peepers hit CIV 3 at every site where they called.
Call Index Values for each species at each site, Pictured Rocks National Lakeshore, 2019. NPS
What's next
The recorders switch on every spring to catch frogs and toads waking from winter and looking for mates. Data since 2019 are being analyzed, and the Park Service plans regular updates on the lakeshore's amphibians. More: Great Lakes Network amphibian monitoring · PDF of this report.
Sources
Based on "Amphibian Monitoring at Pictured Rocks National Lakeshore, 2019," National Park Service; a work of the United States government in the public domain.
In these publicationsPictured Rocks National Lakeshore
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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