Have an ear for the wild? You might be able to help the state of Minnesota as it again surveys the frog and toad population — and gains a keener understanding of Minnesota's ecosystems.

"Frogs and toads are indicators of habitat quality and provide valuable information on the condition of Minnesota's wetlands. Volunteers' reports help us track the health of the state's frog and toad populations and, therefore, wetlands and water quality," said Janine Kohn, project coordinator, in a news release from the Department of Natural Resources.

The survey is in its 20th year and relies on volunteers to do "listening surveys" on designated routes, on three evenings between March and July. There currently are 56 vacant routes, notably in the state's southwest, Kohn said in an e-mail. There are 251 routes in Minnesota.

Kohn said most frog and toad populations have remained steady, but the surveys have been revealing nonetheless. She said surveys have shown a rise in the number of American bullfrogs. "Bullfrogs are only native to the tip of the southeast corner of Minnesota, but their range has expanded to other parts of the state," she said.

The frogs are considered invasive to areas beyond their range.

Too, the numbers of spring peepers and gray tree frogs have declined. "There are various suggestions on the decline of the gray tree frog, but as far as the spring peepers (in metro areas), we have discovered that they are more sensitive to urbanization than other species of frogs and toads," Kohn said.

This year, people have access to a new mapping application to sign up, choose routes and print off calling survey sheets and other related documents.

Find the application online at bit.ly/frgsurv, or call 651-259-5905 for more information.