2009-07-23_AgendaPacket - Laserfiche WebLink

Home

. ®. Contiiiuert front page 4 there is some overlapping of calls, and 3 -calls are constant, continuous and overlapping. For example, chorus frogs were a 3 at every stop on Brueske's and Hartman's run, and wood Frogs were an intermittent 1, audible only at some stops. They iden- tified no other species. Recording the volume of amphibian voices atpre-determined spots repeat- edly "is a way of measuring change aver time," said Larson. Volunteers are asked to travel their assigned route three times each year. The first is done in the spring when water temps rise above 50 degrees, the second in early to mid-summer when waters are generally above 60, and the final run later in summer when Iakes and wetlands reach 70 degrees. Frog calls are mainly pro- duced by males attempting to attract Females. Most species do so by inflating their vocal sacs, forcing air over their vocal chords. Friends since they attended St. John's University a decade ago, Hartman and Brueske have been listening to frog and toad calls for four years. They circle Lebanon Hills on a pre- designated twa-hour route that takes them from a lakeshare to deep in the midst of a housing development, to a forested dirt road and finally to a highway overpass. Volunteers are only required to know the frog calls relevant to their part of the state. This process makes it fairly easy to flag outliers. On that night in Lebanon Hills, Brueske and Hartman detected only two relatively common species, cho- rus frogs and wood frogs. "We know they know their calls," Lar- son said of the volunteers who make the survey possible. "And they really want to help, so they do study-every once in a while, I get .mp3 clips that people have recorded, asking me what frog this could be." True to form, Brueske and Hartman carried the official DNR frog call CD in the car with them. To make sure they ~'®h~ar s®ene fr®g calls, ®r t® take the quiz on ~-hich calls belong to which frogs, visit the tVlinnesota Frog and °foad Calling Survey enrebsite: ww~nr.dnr.state.mrt.us/volunteering/ frogtoad_survey. ~ ~, , ter- -^--- ~ 6 - _ -~ a~ : Is `~n~-; e ~ ~ ~~f~ ' ~ ~~. ~ ^~_ ; ~ _ ~~., a ' A'; 9 Wnnd frnn Hartman, a biology teacher at Mahtomedi Leanung Center, and Bnaeske, who works for the Min- nesota Department of Health and holds a degree in chemistry, do their best to assure the validity of their results. Before volunteers can have their data logged in the official DNR record, they must pass an online test in which they listen to audio recordings of multiple frog species and attempt to identify their calls. "Ninety-two percent this year," Brueske said, half bragging, half joking. were hearing wood frogs, which have become rarer on the early spring run, they listened intently to track after track of frogs recorded in the wild. Of all the calls, Hartman said, the American bullfrog (an invasive species in most of Minnesota) is the most distinc- tive. "It sounds like a slow tightsaber," he said. Wood frogs sound a bit like a duck quacking, and spring peepers sound almost alien, high pitched and far-away. Brueske's and Hartman's Lebanon Hills route is one of the original Twin Cities Metro area routes designated by volunteers in the early 1990s. Most of the routes statewide were randomly assigned via a computer model in 1998. The placement model, a result of a partnership with the National Amphib- ian Monitoring Program and the United States Geological Survey, scattered approximately 250 dots on a map of the state, according to potential volunteer density. The participants then fleshed out the routes, and the routes have been run consistently, with as Iittle change as pos- sible, Ear the last 11 years. The DNR publishes ayear-end report based on survey data, available at the sur- vey`s home page: www.dnr.state.mn.us/ volunteering / frogtoad survey, But due to the relative infancy of the survey, data analysis has been Fairly minimal. The annual report Lists spe- cies trends as rising, falling, or stable, but it is done as a single, statewide analysis. Larson hopes to do more with the data in coming years, including ana- lyzing populations by region. She believes, For example, that spring peepers, once com- mon in the Twin Cities, seldom are heard by volunteers now. The most certain trend in the data, the increase and spread of American bullfrogs, comes from bullfrogs being sold as pets and bullfrog tadpoles being sold as fishing bait, according to Larson. But certainty in the apparent decline in spring peepers and tree frogs is proving to be more difficult. "It looks like a 10 percent drop, but it's completely dependent on weather, and we've had some odd springs," Larson said. Amore average spring this year, in terms of both temperature and precipita- tion, could show both species returning to previous levels Larson said. Or this year's data, she said, could shed more light on whether Minnesota is "seeing a real, bio- logical decline" in amphibian species. l`~`~ FACETS June 2009 ~~;~