Free Press photos by John Cross
While there are anecdotal reports of declining populations of northern leopard frogs, data gathered from the DNR's annual frog and toad survey suggest they are doing fine.
A male chorus frog was successful in attracting a mate with his calls.
Minnesota State University graduate students Zack Bateson of Eveleth (left) and Lucas Wandrie of Waseca check out the edge of a wetland while conducting a frog and toad survey for the DNR.
A male chorus frog was successful in attracting a mate with his calls.
Male northern leopard frogs compete for the attention of females by calling from the edge of a wetland near Duck Lake.
Now, there's nothing unusual about a couple of college students going out on a Friday night.
Nor would it be out of the ordinary if they took a keen interest in the sorts of courting rituals that ultimately might attract a mate.
So one might have assumed that Minnesota State University graduate students Lucas Wandrie and Zack Bateson might be headed to popular night spots when the biology majors headed out last Friday evening.
But the kind of night spots they were checking out were of the dark and damp kind.
As volunteers for the Minnesota Department of Natural Resources Frog and Toad Survey, armed with a Global Positioning System device, a thermometer, headlamps and a clip board, they drove off into the darkness to count the mating calls of male frogs and toads along a predetermined route that would take them to 10 different wetlands in and around Mankato.
The first stop at 9:45 p.m. on the route was the ditch near Thompson Ravine Road. With little vegetation along the banks, neither expected to hear much. As expected, we were met only with silence in the evening darkness.
Volunteers note the time, the air and if possible, water temperatures. They then spend at least five minutes listening for the various amphibious species.
To aid in identification, volunteers receive a CD of the various calls to familiarize themselves with and are given an online identification quiz.
In Wandrie's case, he already was very familiar with the various species' calls after a previous summer of conducting amphibian surveys for the DNR.
Surveyors quantify the calls in three levels: At level 1, calls from single individuals can be detected; at level 2, individuals can still be detected but calls overlap with others; at level 3, calls are full-blown chorus where individuals and their calls cannot be discerned.
On a second stop, a small wetland in a housing development not too far from the Mankato Golf Club, the calls of chorus frogs came through the open car windows, even as we rolled up. Bateson tallied a level 2 on the survey form.
"We'll probably hear mostly chorus frogs on this survey," he said.
Volunteers are expected to make two more surveys within predetermined time frames later in the summer to tally the various species that become active as summer progresses.
At all of the remaining stops, chorus frogs were heard in various numbers. Northern leopard frogs with their lower, slower calls also were detected.
At one stop, a wetland east of Mankato along County Road 2, a high, steady trilling sound could be heard above the calls of the chorus frogs.
"Toads," Wandrie said. "It's kind of early for them but it's probably because the water here is shallower and warmer."
With the exception of the first stop in Mankato where nothing was heard and another where a few sporadic calls only achieved the level one status, every other stop measured a level two.
Nearly midnight and approaching the 10th and final survey site near Lake Washington, Wandrie made a prediction: "This one," he said, "will be the mother lode."
Sure enough, the thick stand of several acres of solid cattails was a nonstop high-pitched roar of chorus frogs, through which the lower calls of leopard frogs occasionally could be heard.
"Definitely a three," Bateson said, marking it down on the clipboard in the red light cast by his headlamp.
How many chorus frogs might be out there? Thousands, the both agreed, as we headed back to Wandrie's van.
"And remember, it's only the males so we're only hearing half of them," he said.
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