Frog calling volunteers document the American bullfrog’s comeback

Wisconsin Frog and Toad Survey gets underway soon

MADISON – Wisconsin’s largest frog appears to be staging a comeback, a welcome trend documented over the last generation by hundreds of volunteers who’ve travelled roads near rivers, lakes and wetlands listening for the breeding calls of male frogs and toads.

The Wisconsin Frog and Toad Survey gets underway in coming weeks, and volunteers are likely to hear more of the booming call of the American bullfrog this summer when its mating season begins.

Volunteers for the Wisconsin Frog and Toad Survey have documented what appears to be a comeback by the state's largest frog, the American bullfrog.  - Photo credit: Andrew Badje
Volunteers for the Wisconsin Frog and Toad Survey have documented what appears to be a comeback by the state’s largest frog, the American bullfrog. Photo credit: Andrew Badje

Ranging from 3.5 inches to 8.5 inches from snout to vent, the American bullfrog is the largest frog in Wisconsin and North America and has a foghorn call to match, says Andrew Badje, a Department of Natural Resources conservation biologist who coordinates survey volunteers.

“Our volunteers are increasingly reporting more bullfrog calls since the Wisconsin Frog and Toad Survey began in 1984,” he says. See an animated map showing the increase by typing in the words “American bullfrog.” (exit DNR)

“That’s great news for several reasons,” Badje says. “While American bullfrogs are considered a pest in western states where they’ve been introduced, they are native to Wisconsin and a valuable part of the food chain. Their comeback also shows we can take protective actions and make a difference.”

Bullfrogs were widely used in the 1900s for biological supply companies, the bait industry, and for use in the food industry as “frog legs.” Regulations enacted by DNR have helped prevent the over-harvesting of adult bullfrogs in Wisconsin and have helped the population build again, as have increased conservation education efforts by DNR’s Natural Heritage Conservation program and many partners.

The Wisconsin Frog and Toad survey was initiated in 1981 as a response to known and suspected declines in the 1960s and 1970s in numerous Wisconsin frog species, including the northern leopard frog, American bullfrog, pickerel frog, and Blanchard’s cricket frog. Due whole-heartedly to Wisconsin’s dedicated volunteer-base, the survey is the longest running citizen science amphibian calling survey in North America, Badje says.

“Over the years, these citizen scientists have helped DNR conservation biologists define the distribution, status, and population trends of all 12 frog and toad species in the state,” Badje says. Volunteers have logged more than 8,700 survey nights and 87,000 site visits since the survey began.

Their data have documented the American bullfrogs’ good news in Wisconsin, but also a downward trend for the northern leopard frog over the course of the survey. Spring peepers, boreal chorus frogs and green frogs have been on more stable paths since the survey began. Read more about the survey and its results in the April 2016 Wisconsin Natural Resources magazine.

Some frog calling routes still need volunteers as do phenology surveys

Volunteers survey three nights a year along a pre-set route in each early spring, late spring, and early summer. Each volunteer makes 10 stops per night (five minutes at each site) and documents the species calling and the relative abundance of each species.

A few 2018 Wisconsin Frog and Toad Survey routes are not yet spoken for; see available routes (green icon) on the Wisconsin Frog and Toad Survey’s website [EXIT DNR]. Interested volunteers also can ask Wisconsin Frog and Toad Survey coordinators about open routes or ask to be placed on a waiting list for future years as desired routes or counties become available.

Volunteers also are invited to participate in phenology surveys to help monitor when frogs and toads first start calling. Phenology volunteers choose one wetland to monitor throughout the frog calling season and record data as often as possible for five minutes per night.