Scientists probing a mysterious spate of bald eagle deaths along Thurmond Lake had good news - and more bad news - this week.
Another dead eagle, the 13th found since Thanksgiving, was discovered along a shoreline in Lincoln County during an aerial search, said Georgia Department of Natural Resources biologist Vic VanSant.
The good news was that searchers also counted five bald eagles at various locations along the 70,000-acre reservoir that appeared healthy and normal.
"We were glad to see the live birds," he said. "We weren't sure how many we'd find, if any at all."
The eagles are dying from a mysterious malady called Avian Vacuolar Myelinopathy, or AVM, that was first diagnosed at DeGray's Lake in Arkansas five years ago.
Despite intense efforts by some of the most advanced research facilities in the nation, the precise cause of AVM remains unknown.
The symptoms - wobbly, erratic behavior and inability to fly - are caused by microscopic lesions that destroy the brain. Ducks and geese also have been found with AVM, which is always fatal.
Although scientists remain unsure of the cause, the suspicion is that small waterfowl called coots ingest some sort of algae or aquatic plant that produces a toxin fatal to eagles, which prey on coots.
Authorities also are investigating possible links between herbicides used at Thurmond and DeGray's lakes to control the noxious weed hydrilla, which grows rapidly and attracts waterfowl such as coots.
"We are indeed looking at whether herbicide treatment may play a part, and perhaps even whether hydrilla itself may play a part," said Army Corps of Engineers spokesman Jim Parker.
The Corps manages both reservoirs, and hires contractors to spray herbicide on hydrilla at both lakes.
However, there is no hard evidence at this point that herbicides could be responsible, he said.
"One issue in terms of Thurmond Lake is that the application is not very widespread," Mr. Parker said. "We only treated about 60 acres of more than 4,000 acres of hydrilla this year, a relatively small amount."
John Fischer, director of the University of Georgia's Southeastern Cooperative Wildlife Disease Study Center, said he is unsure whether herbicides are linked to the problem.
"Hydrilla is what brings coots in, and eagles eat the coots," he said. "But the thing about treatment of hydrilla is, we also have AVM at lakes where they don't have hydrilla."
Savannah River Ecology Lab scientists in Aiken County also are studying AVM and working to learn more about the condition. A recent survey of 22 coots taken from within Savannah River Site turned up 20 infected birds.
Other institutions involved in AVM research include the National Wildlife Health Center in Madison, Wis., and the Corps of Engineers' Waterways Experiment Station in Vicksburg, Miss.
Anyone finding dead coots or eagles - or who observing eagles acting suspiciously - should notify David Brady, the Army Corps of Engineers biologist, at (800) 944-7207, or Mr. VanSant at (706) 595-4222.
Reach Robert Pavey at (706) 868-1222, Ext. 119.