Surveying the Music of Maryland’s Marshlands
It’s an hour after sunset on Maryland’s Eastern Shore. Glenn Therres, a wildlife biologist and associate director at the Maryland Department of Natural Resources, is up to his usual Friday night routine: prowling the back roads in a pickup truck, surveying frogs.
He pulls off on a swampy roadside near the Miles River and scrambles out to identify several species of amphibians by their trills and grunts.
“Each of the frogs has a unique call,” Therres said. “Some of them are fairly similar but most you can distinguish from each other. So the little rattle-y sound here? Sounds like crickets? Those are called northern cricket frogs. And they really sound like someone taking a can of paint and shaking it and hearing that little ball inside. That’s a cricket frog. The bullfrogs are the kind of ‘mrrp, mrrp, mrrp.”’
Keeping track of frogs, toads, and salamanders is increasingly important because amphibians are in sharp decline around the world. The journal Science recently published a study that found that an invasive species of fungus called "chytrid" is contributing to the decline of more than 500 species of amphibians globally.
To find out what’s happening with amphibians in Maryland, Therres and several colleagues spent five years exploring roadsides, streams, and bogs across the state and compiling what Johns Hopkins University Press recently published as the Maryland Amphibian and Reptile Atlas.
“The amphibian and reptiles project was conducted by a little over 1,000 people,” Therres said. “In total we documented 85 species of native reptiles and amphibians and a handful of exotic species.”
The good news is that – for whatever reason—most amphibian populations remain robust in Maryland – with little signs of the catastrophic die-offs seen elsewhere around the world. Spring peepers, for example, are in decline in Pennsylvania and Delaware, but still sing by the millions in the Land of Pleasant Living.
There are some exceptions –with sharp declines, for example, in upland chorus frogs in the Baltimore/Washington corridor because of suburban sprawl. And sea level rise on Maryland’s Eastern Shore is washing away the already limited habitat of the Eastern Narrow Mounted Toad in low-lying Dorchester County.
And then, during the course of their roadside research for the Amphibian and Reptile Atlas, there were a few new local species that Therres and his fellow surveyors stumbled across.
“We did get a report of a boa constrictor in Anne Arundel County,” Therres said. “This, most likely, was a snake released by a pet owner, or it escaped. When our volunteer went to go look for it, it was dead in an area where there was some homeless folks. And one of the homeless guys claimed that the snake ate his buddy.”
That last part could not be confirmed by the scientists, who did not detect any unusual bulges in the belly of the boa. Unless, of course, the man’s friend was very small – a mouse, perhaps, which would be beneath the scope of the research.
After an evening of driving around in his pickup truck, we were in a different swamp, surrounded by fowler’s toads and mobbed by mosquitoes and I asked: So, why spend Friday nights with frogs?
“Amphibians? Why should we care so much about amphibians?” Therres asked. “Most amphibians depend on water and water quality. And most of human life and life in general depends on water and water quality. So they are kind of barometers to what’s going on in the environment.”
In other words, amphibians are canaries in the coal mine of our world. And these canaries are still singing.
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