NEW ELLENTON - Erin Clark, lying on her stomach, reached into an oval burrow half-hidden among pine straw and wiregrass.
"They're strong - really strong," the Savannah River Ecology Lab graduate student said, tugging mightily at something wedged inside.
Her colleague, Kurt Buhlmann, gave her a hand. After a minute of team tugging, the den's occupant - an adult gopher tortoise - was pulled reluctantly into view.
"This one's a male, a mature male," said Dr. Buhlmann, a visiting scientist at the lab. The turtle, held aloft, blinked with shy reptilian eyes.
Dr. Buhlmann, who works for Washington, D.C.-based Conservation International, is working with the lab and the U.S. Forest Service in a first-of-its-kind study involving an entire colony of the reclusive creatures.
Last year, as land was cleared for an industrial park in McIntosh County, Ga., more than 100 of the rare tortoises were discovered and rescued from certain death.
The tortoises now live within a 2,500-acre segment of the 300-square-mile Savannah River Site in a habitat that includes longleaf pine, sandy soil and wiregrass - their preferred browse.
Although anecdotal evidence indicates gopher tortoises once occupied longleaf pine plantations in Aiken County, they haven't been documented in significant numbers since the 1920s, Dr. Buhlmann said.
The current study, however, is likely to restore them. Scientists are trying to gauge how far the relocated turtles will wander when released - and also decipher their social and reproductive habits.
Adults have been fitted with two radio transmitters attached with glue and wired to antennas at the backs of their shells. Bar code scanning chips also are attached to them.
"We're learning a lot about them already," he said. "We know which males like which females, and we know which females visit which males' burrows, and how often."
They also have learned that some males don't care for other males.
"They butt heads," Dr. Buhlmann said, laughing.
The study at the ecology lab has several objectives.
A primary thrust is to determine whether relocated gopher tortoises will remain where they are placed. The animals have a powerful homing instinct that sometimes gets them killed when they wander away from new homes in efforts to return to where they were raised.
Ms. Clark is watching three groups of gopher tortoises - all from the salvaged south Georgia colony.
One group was allowed to roam almost instantly, and many of them crawled long distances, ending up in swamps, crossing highways - and even waddling across a shooting range.
A second group, enclosed within a 2.5-acre area surrounded by fencing, was kept within the area for more than three months. The fencing was removed earlier this week, freeing them to wander.
"We'll know in a few days what they do," Ms. Clark said. "We hope they stay here."
A third group remains confined within a 2.5-acre fenced area; that fence will be removed in a few months to see whether the extra months of confinement affect the turtles willingness to stay put.
The study also hopes to develop "assurance colonies" of the rare tortoises that can help sustain their populations if colonies are lost elsewhere and to pilot turtle survival studies that will be repeated in other parts of the world, where many turtle species face extinction.
The project at SRS also will add another missing ingredient to the longleaf pine/wiregrass habitat that has vanished across much of the South, said U.S. Forest Service technician Pete Johnston.
The gopher tortoise study area includes another rare species - the red-cockaded woodpecker - which, like the tortoise, is vanishing because of loss of suitable habitat.
Reach Robert Pavey at (706) 868-1222, Ext. 119, or firstname.lastname@example.org.