ATHENS, GEORGIA, U.S.A. - Researchers have been trying to learn more about a plant that has invaded lakes across Georgia and the Southeast, contributing to the deaths of eagles and other birds.
The hydrilla has helped to cause the deaths of American bald eagles and thousands of other water birds over the past 25 years, scientists say.
The plant isn't killing the birds directly, but is providing a home for a new kind of cyanobacteria that produces a lethal toxin, The Athens Banner-Herald reported.
Scientists have been studying the issue after bald eagle carcasses were being found at a man-made lake in Arkansas. An increasing number of afflicted birds then began showing up in Arkansas, Georgia, and other states across the South.
There were reports of injuries - the loss of motor control in eagles and in a water bird called the coot. Their symptoms included wings that twitch but don't flap, and difficultly maintaining balance.
Necropsies found that the affected eagles and coots showed peculiar lesions that made their brains look like sponges, the Athens newspaper reported.
Wildlife scientists had a name - Avian Vacuolar Myelinopathy, or AVM - but lacked crucial details on what was causing it.
The problem has been especially acute at Thurmond Lake, a man-made reservoir on the Savannah River between Georgia and South Carolina, the newspaper reported.
University of Georgia professor Susan Wilde saw patterns. The lakes where eagles were dying of AVM are man-made, and they had been heavily invaded by hydrilla. The coots were eating the hydrilla, and the eagles found easy prey in the disabled coots.
Wilde's hypothesis: The coots could be ingesting some neurotoxin associated with the plants, then passing on the toxin when the eagles ate them. Wilde also found that a previously unknown kind of cyanobacteria was growing on the underside of the spreading hydrilla leaves. That could be producing lethal toxins.
In 2014, nearly two decades after the neurological disease first showed up, Wilde and her colleagues had a name for the cyanobacteria: Aetokthonos Hydrillicola, or eagle-killer. They'd also isolated the toxin it produces.
On Thurmond Lake, more than 105 AVM eagle deaths have been confirmed so far, and scientists believe the death toll is higher since many animal carcasses are never found.
Lake managers are trying strategies to beat back the plant invader and its toxic companion. They've had some success stocking Thurmond and other lakes with a kind of sterile grass-eating carp to gnaw away at the hydrilla, combined with sowing native water plants. Lake managers are also using chemical killers on the plants, though that carries its own set of environmental risks.