The language of frogs — it’s more than just ‘ribbit’

Posted April 30, 2014, at 10:35 a.m.
Last modified April 30, 2014, at 2:19 p.m.

Maine is home to nine species of frogs, and each has its own song.

The spring peeper lets out a high-pitched “peep.” The pickerel frog emits a low snore. And the green frog sounds like it’s trying to spit and gulp at the same time — “glug, glug, glug.”

Recently, a handful of Mainers have been learning these amphibian calls on their path to become the state’s first volunteer frog monitors for Frogwatch USA. This spring and summer, they will seek frogs and toads in local wetlands, and they will do it by ear.

For them, “ribbit” just became a whole lot more complicated.

“Science is usually done by scientists, but there’s a limited number of us. We can’t be everywhere at once, so citizen science is a great way to get other people involved so they can get out there and help us collect data,” said Katelin Craven, FrogWatch USA coordinator for Maine’s Lower Penobscot chapter, at a recent frog monitor training session at Hirundo Wildlife Refuge in Alton.

“Each one of you knows of a little wetland or a pond that nobody else knows about or is just in your backyard or neighborhood,” said Craven to the nine volunteers gathered for training. “So that helps us collect data all over Maine.”

Sitting around a table in Hirundo’s Parker Reed Shelter, the volunteers dutifully jotted down notes as Craven and Hirundo naturalist Gudrun Keszocze worked through a slideshow about Maine’s nine Anuran (frog and toad) species and the various wetlands in which they can be found.

Outside the shelter, rain dimpled the calm surface of Lac D’Or, a man-made pond surrounded by cattails — home to green frogs and American bullfrogs, Keszocze said. Hirundo, a 24,000-acre nature preserve, contains a variety of wetlands that amphibians inhabit, including a domed bog, maple and juniper swamps, Dead and Pushaw streams, and ever-changing beaver ponds.

In addition to holding an integral place in the wetland food web, biologists have long considered frogs to be indicators of ecosystem health. More so than other creatures, frogs are sensitive to the environment because their permeable skin allows pollutants in the water and on land to enter their bodies.

Over the past 20 years, frog populations have been dramatically declining all over the world. In fact, almost one-third of the amphibian species in the world are threatened, and in the U.S., 25 amphibians are listed under the Endangered Species Act, according to FrogWatch USA.

Naturally, biologists are eager to learn why this is happening, not only to save the frogs, but to preserve natural environments as a whole. In addition to pollutants, primary causes of the decline of amphibian populations are thought to be habitat loss and fragmentation, invasive species, climate disruption, parasites and disease.

FrogWatch USA is the Association of Zoos and Aquariums’ flagship citizen science program and has been underway, in one form or another, for more than 10 years. But it took until this year for Maine to join the effort.

“They have really good data for a lot of the U.S. However, Maine was a completely empty slate [as of last year]. No one had ever done any reporting in Maine at all,” said Craven to the group of volunteers. “You guys are getting in on the ground floor and can watch it grow.”

The data collected by FrogWatch USA is used across the country to describe local species diversity and inform local wetland management decisions. The study gives biologists more insight into amphibian behavior, population trends and responses to climate change.

As the four-hour training session progressed at Hirundo, the volunteers began learning the different frog calls. The raspy, duck-like quacking of wood frogs filled the room as Craven played a recording of their song.

“I like to make funny plays on words to remember the calls,” Craven said. “For example, for wood frogs, I think of wood ducks. For bullfrogs, I think of a bull mooing.”

Fortunately, the times of year that frogs sing are staggered.

In Maine, as the landscape thaws in April, wood frogs and spring peepers emerge and begin calling out for mates and defending tiny territories. It’s not until mid-May that the American toad, northern leopard frog and pickerel frog take over the chorus. And in early July, the American bullfrog, gray tree frog, green frog and mink frog take the stage in a cacophony of trills, glugs, clacks and moos.

After undergoing a training session, volunteer frog monitors select at least one wetland location to monitor for frogs and toads throughout the spring and summer, and they will enter their data at, where all the data collected throughout the country is available to the public.

If you are interested in becoming a volunteer frog monitor, here are upcoming training sessions in Maine:

— 7:30-9 p.m. Saturday, May 10, at the school building on Water Street in Grand Lake Stream, organized by the Downeast Lakes Land Trust. For information, visit

— 9 a.m.-12:30 p.m. Tuesday, May 13, at Liberty Library in Liberty. For information, email

— 1-5 p.m. Sunday, May 18, at Hirundo Wildlife Refuge in Alton. For information, email or visit