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image of lilypad covered pond at twilight.

Sense of Place: Attuned to Frogs

A wetlands researcher steps into the muck and finally hears the frogs.

By Judy Helgen

Late one spring evening, I turned off a highway northeast of the Twin Cities and drove down an unlit gravel road into a wildlife management area to record frog calls. Harried by the pressures of my research work at the Minnesota Pollution Control Agency, I wondered if taping frogs at night was too much to do. I wanted the audiotape to help raise awareness of wetlands biology among volunteers we were training to monitor wetlands health.

Hear the frogs and toads of Minnesota!

Listen to Minnesota's spring chorus.

Take the Minnesota frog and toad calling quiz (select "Minnesota" to start).

Join the DNR's Frog and Toad Calling Survey.

I stopped to unhitch a chain that hung across the access road and drove slowly through the woods to a wetland, which I knew was rich in species of invertebrates. I turned off the car radio, doused the headlights, and stared into the darkness to rest momentarily. Slowly, I opened the door and emerged from the car into a black soup of night that pulsed with high-pitched, urgent calls of frogs.

Spring peepers, lots of them! Sometimes, the slam of a car door can silence singing frogs. Not that night; these peepers were too far gone. Their penetrating music, a rising host of birdlike whistles, filled the moist darkness that swirled around me. I felt drawn into a primitive world of ancient passion, amphibian-style. My brain was so flooded by the chorusing frogs, I could hardly think.

Early American settlers wrote of sleepless nights, of frogs driving them almost crazy during spring. I read that French aristocrats made peasants stay out all night to beat on marsh plants to quiet the frogs, so the nobles could sleep. Now I could understand why, and it must have been the ceaseless, high decibel songs of spring peepers.

How on earth could a frog barely as long as a standard paper clip make such intense, piercing sounds, I wondered. And why did the male frogs pack themselves so closely together in certain clumps of trees beside the wetland? Weren't they competing to attract females? Why not spread out? It didn't make sense.

As I pulled on hip-high rubber waders and slipped on my backpack loaded with recording equipment, I recalled listening to peepers with my dad when I was a child in New England. I missed talking with him, and I missed listening to these trumpeters of spring, which I rarely heard anymore unless I got out of the city. Voices of people came into my head, Minnesotans I'd met during the course of my work. They'd told me they no longer heard spring peepers where they used to. Their voices expressed a puzzled sadness.

Minnesota's peepers may be on a downturn, especially in urban areas. What lies ahead for these musical frogs? Will their habitat of shrubs, trees, and shallow wetlands disappear because of development and farming? Will misguided, turf-loving landowners rake away the woody, leafy debris that peepers need for protective cover to survive the winter?

Intensity Rating

I tried to focus on the task at hand, but the unrelenting high-pitched sounds distracted me. Mesmerized by the peepers, I'd lost track of time. It was getting late, and I couldn't be there all night. I had to get busy with my taping project. Mosquitoes whined around my face. I wanted to leave and go home to sleep off the fatigue from my job. I took a few cautious steps to the edge of the wetland, flipped on the microphone, and punched the record button.

I pointed the elongated shotgun mike toward the woods that bordered the wetland. The recorder's red lights flickered up and down: plenty of signal.

The calls overlapped so much that individuals couldn't possibly be distinguished. I rated the intensity of this chorus a "three" under the guidelines for the Minnesota Frog and Toad Survey. A rating of "one" would indicate the individual calls had no overlap. "Two" would mean some overlap, but individuals could be heard.

I began to feel more focused and less disoriented by the overwhelming intensity of the peepers. I was there for my work; I had a purpose. I'd be shipping the audiotapes to Cornell University's Macaulay Library of Natural Sounds, which archives recordings of frog calls and bird songs. Using my script with the frog calls arranged by season, the Cornell lab would create a tape of Minnesota frogs that I could give to our wetland volunteers.

The calls would be sequenced on the tape in the chronology of the spring breeding season: first, spring peepers, chorus frogs, and wood frogs; then leopard frogs, American toads, and gray tree frogs; and last, green frogs, mink frogs, and bullfrogs.

I worried about the early season breeders, especially wood frogs and spring peepers, because they typically reproduce in temporary wetlands, also called vernal pools or ephemeral wetlands. These shallow pools, which dry down most years, are fragile and easily destroyed by developers or ruined by stormwater runoff. When people excavate a vernal pool to create a "wildlife" pond to hold fish, they unwittingly destroy amphibian-breeding sites because fish gobble up tadpoles.

Plaintive Call

Suddenly, an unusual low-pitched, burbling call caught my attention. I wanted to record it. This frog's sound came from muck level. I stepped gingerly down into the wetland, trying to be stealthy. I had already waded here several times to sample invertebrates during daylight. It was tricky even then, because large hummocks of tussock sedge protruded a foot or two above the mucky bottom. If you tried to walk on top of them, they could pitch you over. Better at night to stay down in the muck, especially with my costly recording equipment.

After a few minutes, the frog's plaintive but musical burble started up again, now only a few feet away. A peeper, I suspected, possibly a male cooing at a female he'd attracted, ready to mate. I fumbled with the recorder, pointed the mike, and captured the solitary sounds.

Relieved I hadn't fallen, I retreated toward solid ground. I wondered what possessed me to wade into a wetland alone at night, when standard procedure for our MPCA fieldwork was never to sample wetlands by ourselves. It's risky to step through a floating mat of vegetation over deep water, or to fall face down -- as I once did -- in mud too soft to push oneself up by hand.

I climbed up the bank and scrambled through the shoreline shrubs and trees back to my car. As I pulled off my waders and stashed my gear, I felt the frogs had been calling me for something more than making a tape recording. At the office, I viewed frogs intellectually, as indicators of good wetlands and as teaching tools. But now, after listening to them at night, I'd developed a deeper empathy for their fragility and vulnerability, for their need to have safe and healthy habitats. My reflections continued as I drove out, hooked the chain back across the gravel road, and headed onto the highway toward home.

For how many millions of years have frogs survived on earth? For how many thousands of years have male frogs been calling in Minnesota -- since the glaciers retreated, leaving behind a wealth of shallow wetlands? The calls of the frogs pulled me into a deeper kind of connection. I listened. And finally, I heard.

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