Listening for the frog songs

Environment: Howard volunteers spend evenings surveying the health of the amphibian population.

April 09, 2003|By Stephanie Choy | Stephanie Choy,SUN STAFF

As the sun fell lower into the horizon one recent evening, the sounds of frog and toad mating calls filled the air. It was singles night at the Middle Patuxent Environmental Center.

The frogs didn't know it, but they were taking part in a giant science experiment called Frogwatch USA - a study that examines declining amphibian populations across the United States.

Sometimes called "green canaries," frogs and toads are biological indicators that show how human activities affect water quality, wildlife habitat and other aspects of the environment. The porous skin of frogs and toads makes them vulnerable to environmental changes; the rapid growth in agriculture, industry and urban development has been linked to a decline in the amphibian population.

Frogwatch USA was developed by the United States Geological Survey's (USGS) Patuxent Wildlife Research Center in Laurel in 1999 as a way to monitor the frog and toad population. The data from Frogwatch USA is compiled by the USGS to find patterns in population distribution, trends in individual wetlands and breeding habits of frogs and toads.

In an ominous sign of the importance of that research, 12 species were studied and recorded last year, down three species from the year before. The USGS has not come out with an interpretation of the decline, but it clearly reflects a larger pattern.

Frog populations appear to be in serious danger from the Caribbean islands to Africa, tropical Asia, China and Central America, according to a recent report in Froglog, the amphibian assessment newsletter.

In Howard County, volunteers take frog-calling surveys at least twice a month, from mid-March through mid-August. They visit 35 sediment ponds or wetland areas in the county that are considered likely frog habitats.

After taking measurements of the temperature, wind speed, precipitation and weather, participants listen for three minutes and record the calls they hear on a standardized data sheet.

This will be Pam Franks' fourth year participating in Howard Frogwatch. A mathematician by day, Franks spends nights tromping through creeks along the Middle Patuxent River. A self-described "nature freak and freak of nature," she jumped at the chance to join the watch after seeing a newspaper advertisement seeking volunteers.

To prepare for the survey, participants receive training packets that include the research protocol and, more important, a cassette tape loaded with frog calls.

This is essential because "most people don't know the difference between a frog and a toad and a cricket!" said Sue Muller, the director of Howard County's frog-watching program.

But learning to recognize different frog calls is not too hard, Muller said. Families occasionally volunteer together and the children sometimes use Frogwatch USA as a science project to complete school requirements for community service.

Franks had no experience with frogs when she began volunteering, but learned over time how to differentiate among the calls. "I actually identify frogs better by sound than by sight," she said.

On this night, the frogs are deafening. Although many of them are heard, none is visible. "They're right in front of my face, but I can't see them," says Franks, shining a flashlight into the mud puddles. "I saw four last night."

The spring peepers are out in full blast, their sharp, bird-like peeps drowning out the rushing of water in the river. But the wood frogs and pickerel frogs, which are common to this area, are not speaking up.

On the walk back to her car, Franks perks up. "Did you hear that?"

The low, barely audible call of the wood frog is heard under the din of the peepers. Franks quickly checks the time and temperature to record later. The wood frog warrants another trek back down to the creek.

It is completely dark, but Franks navigates down the path by memory, without the help of a flashlight.

The benefits of Frogwatch USA reach beyond the breeding habits of frogs

Although the required time for observation is three minutes, this night's trip lasts two hours. The stars are twinkling, bats fly overhead and geese honk vehemently in the pond.

"This is my house," said Franks of her observation site. "It may sound hokey, but I believe that nature can restore your soul."

Frogwatch USA compiles data from across the country through the Frogwatch USA Web site ( app/index.htm).

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