The bell-like calls of green tree frogs set a steady rhythm for a nocturnal symphony of natural sounds in a field off Ben Hill Griffin Parkway south of FGCU. Florida cricket frogs chime in with chirps that sound like glass marbles clacking together. At random intervals, a pig frog grunts a few bass notes in counterpoint.
These courting calls are music to Win Everham’s ears. “There’s a lot of interesting sex going on out there,” he whispers.
But the FGCU environmental studies professor and his Frog Watch volunteers are not peeping toms out on a muggy, buggy summer night to watch frogs get frisky. They’re there to listen to their love songs.
Once a month from June through September, when rainy season downpours leave standing puddles ideal for frog and toad spawning, the Southwest Florida Amphibian Monitoring Network, aka Frog Watch, hits the road.
Trained volunteers travel nine established routes in three counties to check on the status of croaking critter populations. They rate the intensity of mating calls at 12 stops on each route, based on whether they hear solos or a chorus of overlapping calls. They note the different species they hear. They observe weather and sky conditions, traffic noise, water levels and major changes to habitat.
The collected data helps scientists document the status of indigenous amphibians, which are declining around the world. Across the United States, amphibian populations fell by 3.7 percent annually from 2002 to 2011, according to U.S. Geological Survey data. “Amphibian declines may be more widespread and severe than previously realized,” the report states.
Such news is cause for concern about these sentinel species as well as the state of the environment.
“Frogs are an excellent indicator of the ecosystem’s health – wetlands, especially,” says ecologist David Ceilley, a research associate in FGCU’s Department of Marine and Ecological Sciences who has been part of Frog Watch since it began in 2000. “Frogs are the canary in the coal mine in terms of the health of the environment. If they disappear, it’s a signal that something’s wrong.”
In Southwest Florida, very little information exists on amphibian diversity, distribution, abundance and ecology. Frog Watch is meant to fill that void and provide insight into how frogs and toads are affected by habitat loss and hydrology changes due to development as well as factors such as climate change, drought, natural population fluctuations and introduction of non-native species. The first decade of reporting revealed a slight decline in some native species and a slight increase in exotic species, but the scientists leading the effort have to be careful about drawing conclusions until more information is gathered.
“Just because we don’t hear them doesn’t mean they’re gone,” Everham says. “They could still be there, but we can’t hear them over the traffic. We’re just addressing a piece of the puzzle. We don’t know the whole story. We don’t know where it’s going.”