For 25 years a mysterious killer is on the run in southern America, responsible for the deaths of more than 100 eagles and thousands of other birds. The first victims were found in the fall of 1994 and winter of 1995, when 29 bald eagles died in or near Lake DeGray, Arkansas. At first, the birds seemed untouched. But during an autopsy, scientists found lesions in their brains and spinal cord, a condition they called avian vacuolar myelinopathy (AVM). Researchers at the Department of Fish and Wildlife looked for diseases or toxins like DDT that could cause this debilitating disease, but found nothing.
The mystery remained unsolved.
The killer reappeared in the Carolina, Georgia and Texas a few years later. In addition to bald eagles, it had also begun to attack waterfowl such as Canada geese, coots and mallards. First, it prevented the birds from flying. They stumbled around, their wings hanging, looking catatonic or paralyzed. Then – in just five days – they were dead.
Now, in an article published today in Science, an international team of researchers from Germany, the Czech Republic and the United States have finally identified the culprit, a previously unknown neurotoxin called aetokthonotoxin, which can be produced by a deadly combination of invasive plants, opportunistic bacteria and chemical pollution in lakes and reservoirs.
To find this new poison, scientists had to work together as detectives, assess the crime scene, and question suspects. Susan Wilde, a professor of aquatic science at the University of Georgia, first began investigating the mystery in 2001 when 17 bald eagles died in Lake J. Strom Thurmond, a man-made reservoir on the Georgia-South Carolina border . “I had seen the eagle’s death in past events, but this was the reservoir where I had done my dissertation research,” she says. It was an interesting mystery, but it kind of hit home. That was the reservoir I had been working on and I saw many eagles flying overhead. “
When Wilde collected data for her thesis in the mid-1990s, not much vegetation was growing in the reservoir. But when she returned a few years later, the lake had been overtaken by an invasive plant called hydrilla, which is easy to grow and had become a popular plant for aquariums. (Rumor has it that hydrilla was first released in the US in the 1950s when it grew out of an aquarium and someone dumped it in a Florida waterway. Since then, it has become one of the most harmful aquatic plants in the country, thriving in freshwater lakes from Washington to Wisconsin to the Carolina.) Wilde began to wonder if the eagle deaths and the presence of this new plant were related.
But Wilde had to question all possible suspects. She started sampling the water and sediment from the lake for bacteria. She came forward empty-handed. But when she started examining the leaves of the hydrilla plant, she found colonies of a previously unknown cyanobacterium. She called it Aetokthonos hydrillicola, “The eagle-killer who grows on hydrilla.”
