Dan Olson, MPR News 90.3 FM, Published June 14 2013
In frogs’ croaks, volunteer hears environment’s pulse
Frog courtship, that is.
Linck is helping with a state Department of Natural Resources survey gauging the presence of the state’s 14 frog and toad species. She’s listening for the male mating call.
“The females do no calling,” Linck said.
She offers no judgment on the family values of frogs.
“The females, once they lay their eggs, usually disperse pretty quickly, and the males will hang out and be hopeful another female might come by,” she said.
The survey started 19 years ago due to concerns worldwide that amphibian populations were in decline due to habitat destruction, disease and other factors. Results show the state’s frog and toad population is relatively stable with the exception of grey tree frogs and spring peepers, where the number of calls heard is down.
A frog’s life is treacherous – predators, weather, disease and even traffic can take a heavy toll.
“They cross our busy roads, and on a rainy night, thousands will be run over,” Linck said.
Why worry about frogs? Well, for one, experts say, their numbers tell us about the health of our environment.
An early fascination
Linck is one of the original volunteers for the survey. She grew up in suburban Massachusetts captivated by the out-of-doors generally, birds and amphibians specifically, and moved to Minnesota 25 years ago.
In the early years of the state’s annual frog and toad survey, Linck heard anecdotes from neighbors and friends.
“ ‘Oh, I had frogs all over my yard,’ just like they said about salamanders,” Linck recalled. “Now they’re much harder to find.”
As the night goes on, the males come awake and are calling out to available females.
“They are very hard to see (because) they’re so camouflaged. Everyone’s ready to eat a frog so they have to keep out of view,” Linck said.
The popularity of frogs and tadpoles as food for other critters is what makes them interesting for study. DNR herpetologist Carol Hall said tadpoles especially are an important source of food. She said wading birds, raccoons and other frogs make a meal of them. Going the other direction on the food chain, frogs eat a lot of invertebrates.
Others see the frog as the proverbial canary in a coal mine.
Even though Minnesota’s frog and toad population appears to be relatively stable, the amphibian population in some parts of the Amazon basin, Central America and Mexico has declined sharply, with some species apparently disappearing altogether.
In Minnesota the northern cricket frog population is endangered, but Hall said recently a couple of small colonies have been located.
Sick or disappearing frogs raise a red flag. An early flag went up nearly two decades ago when students found deformed frogs in a southern Minnesota wetland.
Since then, several causes have been cited ranging from agricultural chemical use to climate change to parasites.
Linck said tougher state laws have slowed the drainage of wetlands and helped preserve frog habitat. Development and road building “fragment” habitat and isolate frogs as they try travel from wintering to breeding locations.
Hall said frogs and toads are worth saving, she said, not only because of their importance in the food chain but also for potential benefits to humans if research shows ways to make use of their antifungal properties, the ability to regenerate tissue and recover from freezing.