In frogs' croaks, Madeleine Linck hears environment's pulse

Calling survey
Three Rivers Park wildlife technician Madeleine Linck listens during a frog and toad calling survey at Wolsfeld Woods in Orono Sunday, June 2, 2013. Linck has volunteered as a frog and toad surveyor for about 20 years.
MPR Photo/Jeffrey Thompson

Half an hour past sunset in rural western Hennepin County, Madeleine Linck strains her ears. She's listening, believe it or not, for the sounds of courtship.

Frog courtship, that is.

Linck is helping with a 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.


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 remembers anecdotes from neighbors and friends.

Looking for a frog
Three Rivers Park wildlife technician Madeleine Linck looks for a frog calling near a pond in Orono Sunday, June 2, 2013.
MPR Photo/Jeffrey Thompson

" 'Oh, I had frogs all over my yard,' just like they said about salamanders," Linck said. "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.


Frog's and tadpole's popularity as food for other critters is what makes them interesting for study. Minnesota Department of Natural Resources herpetologist Carol Hall said tadpoles especially are an important source of food. She said wading birds, raccoons, even 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.

Wood Frog
A Wood Frog was photographed in central St. Louis County in Minnesota June, 2011.
Courtesy of Carol Hall/MN DNR

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.

The deformities included some frogs with multiple legs, others with missing legs. Hall said frogs' permeable skin makes them highly sensitive to the effects of farm chemicals.


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 wetlands near a road are a critical location for mortality. Wetland drainage, she said, has increased the distance frogs must travel to breed making them vulnerable to predators and dehydration.

Hall said frogs and toads are worth saving 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.

Some species, she said, virtually turn to icicles in the winter time as they crawl into forest duff or decaying trees, create their own anti-freeze, shut down, and then thaw out in the spring.

Linck said property owners can help by cutting back on chemicals and mowing to give frogs a leg up.

"In your back yard you do not have to have a golf course. You can have natural and native, and if each of us does it then there may be some connectivity," Linck said.

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