Posted on 02 April 2015.
Wood frogs are hardy, common, and among the first frogs to begin calling in the spring.
Michigan’s amateur herpetologists will go afield over the course of the next several months, listening for the songs of frogs and toads across the state. This annual survey – now in its 20th year – is proving to be an important tool, as wildlife officials try to keep track of what’s going on with the state’s amphibians.
“Our volunteer survey was kind of looked down upon by the scientific community when it first started,” said Department of Natural Resources wildlife biologist Lori Sargent, who helped design the survey and has headed it up since the beginning.
“Nowadays, our citizen-scientists are being lauded,” she said. “Our data have been used in a number of graduate-degree studies, which is what we hoped—that it would attract the attention of additional researchers.”
The survey is simple. Volunteers follow a 10-stop route—each at least a half-mile away from the previous stop, so the same toads and frogs aren’t being counted—and record which species of amphibian they hear calling. Volunteers conduct the same surveys on three different nights, at least two weeks apart. The surveys give the DNR indications of the direction of population trends for the various species in Michigan.
Green frogs, found statewide, are sometimes mistaken for bullfrogs.
John and Gwen Nystuen of Ann Arbor have participated in the survey every year since it began. The pair used to like to go out and look for amphibians in the spring, so when the survey began, it was right in their wheelhouse.
“We were very happy to join in,” said Gwen, a retired physical therapist. “It’s fun, a very enjoyable thing to do. You hear one kind of frog one year and then you might not hear it the next year.
Each site is different,” she continued. “It’s kind of like an Easter egg hunt—you get surprises.”
Edward and Kathryn Bolt of Grand Rapids have been involved in the survey for about a decade.
“We’ve been interested in various aspects of nature and we’re certainly interested in the long-term prospects for frogs and toads,” said Edward, a retired architect. “Every time we go out to do our survey, it rousts us from the couch. It’s interesting and educational.”
There are two species of toads and 11 species of frogs (or maybe 12, that’s unclear) in Michigan, some of which are common and widespread and others that are rare and found in limited areas.
Both frogs and toads are cold-blooded creatures, which begin life as aquatic larva—known as tadpoles or pollywogs—before metamorphosing into air-breathing, more-terrestrial creatures, losing their tails and developing legs. Toads are more at home in upland environments; frogs largely must remain wet. So you can find toads at quite some distance from wetlands. Frogs will almost always be in or near water.
The surveys begin as soon as spring arrives—usually April but sometimes in March—and continue until June.
“There are species that call only briefly, the first thing in spring then others that don’t start until later,” Sargent explained. “Bullfrogs don’t start until June; deep-water species are later callers.”
In contrast, shallow–water species, especially those that breed in temporary pools, begin as soon as the weather warms so they can reproduce before the nursery areas dry up for the summer. Toads and frogs call for two reasons: to establish territories and attract mates. Only the males call.
Michigan’s two species of toads—the American toad and the Fowler’s toad—are quite similar in appearance. Their calls are the best way to tell them apart, Sargent said, though American toads are more common and widely dispersed while Fowler’s toads are found mostly in sandy habitat. Fowler’s toads appear to be in decline—based on survey results—and could be candidates for listing as a species of special concern.
Among the frogs, spring peepers are the loudest. Found almost everywhere, they’ll call for the longest period—three months. Wood frogs, found statewide, are extremely common and “among the most interesting,” Sargent said. “They’re very hardy; they can tolerate the cold best and are the only frog found in Alaska.”
Bullfrogs are the largest of Michigan’s frogs and are found statewide, but are most common in southern Michigan. They are strong predators. “They’ll eat anything they can catch,” Sargent said, “other frogs, fish, even birds.”
Bullfrogs are the most prized by humans as table fare and may be harvested by those with a fishing license. The season on all amphibians is the last Saturday in May through Nov. 15. The possession limit is 10 amphibians in any combination, though Blanchard’s cricket frogs and boreal tree frogs may not be taken.
Green frogs, which often are mistaken for bullfrogs, are found statewide. They’re among the most able to withstand environmental contaminants, Sargent said.
Mink frogs are found only in the Upper Peninsula and seem to be in decline, according to the surveys. Blanchard’s cricket frogs are the only threatened species in the state. They’re only found in southern Michigan, though they occur in states to the south.
“We hear Blanchard’s cricket frogs a lot,” Bolt said. “We’re unable to provide visual identification because we’re out at night, but they certainly make a unique sound.”
The boreal chorus frog is found only on Isle Royale and has not been recorded in the last couple of years. “We’re not sure what’s going on with them,” Sargent said.
Michigan boasts two species of treefrog—the Eastern gray and the Cope’s treefrog. “Physically they’re identical,” Sargent said, “but their call is different.”
Frogs and toads are considered good indicators of water quality. They breathe through their skin and are sensitive to contaminants, Sargent said. Herpetologists have noticed a decline in the amphibians nationwide since the 1970s.
Michigan has seen declining numbers of frogs, something Sargent says is probably due to a loss of wetland habitat, though there could be other factors, too.
“There are diseases, toxins, even global warming,” she said.
“These animals are ancient,” Sargent said, “They’ve been around for billions of years. They’re very important to the food chain. They not only eat lots of mosquitoes and other bugs, but they’re important food for other animals.”
Some creatures – the hog-nosed snake, for instance—depend entirely on toads for their sustenance, she noted.
Besides their place in the food chain, frogs and toads serve another important purpose, Sargent said.
“They’re the sound of spring,” she said. “I think if they were gone, people would miss them.”
Sargent said additional volunteers are needed this year to conduct the survey in all parts of the state. Those interested in volunteering for the 2015 survey should contact Sargent at firstname.lastname@example.org.
For more information about the frog and toad survey and frogs, toads and other creatures that are supported by the Nongame Wildlife Fund, visit www.michigan.gov/wildlife.