Scientists finally identify deadly toxin that kills birds

Since 25 years, a mysterious killer is on the run in the southern United States, 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 the winter of 1995, when 29 bald eagles died in or near Lake DeGray, Arkansas. At first the birds appeared to be intact. But during an autopsy, scientists found lesions on their brains and spinal cord, a condition they named avian vacuolar myelinopathy (AVM). Researchers from the Department of Fisheries and Wildlife looked for diseases or toxins like DDT that could cause this debilitating disease, but found nothing.

The mystery has not been solved.

The killer reappeared a few years later in the Carolinas, Georgia and Texas. In addition to bald eagles, it had begun to attack water birds such as Canada geese, coots and mallards. First of all, it made the birds unable to fly. They stumbled, their wings fell, they looked catatonic or paralyzed. Then – in as little as 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 has finally identified the culprit, a previously unknown neurotoxin called aetokthonotoxin, which could be produced by a deadly combination of invasive plants, opportunistic bacteria and pollution chemicals in lakes and reservoirs.

To find this new toxin, the scientists had to work together as detectives, assessing the crime scene and questioning the suspects. Susan Wilde, professor of aquatic sciences at the University of Georgia, began investigating the mystery in 2001 when 17 bald eagles died in J. Strom Thurmond Lake, a man-made reservoir on the Georgia-Georgia border. Caroline from the south. “I had seen dead eagles in the past, but this was the reservoir where I had done my thesis research,” she says. “It was an interesting mystery but somehow struck home. This was the tank I had worked on and seen a lot of eagles fly over.

When Wilde collected data for his thesis in the mid-1990s, there was not much vegetation 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 the hydrilla was originally released in the United States in the 1950s when it passed an aquarium and someone dumped it in a Florida waterway. Since then, it has become the one of the nation’s most pernicious aquatic weeds, thriving in freshwater lakes from Washington to Wisconsin to the Carolinas.) Wilde began to wonder if the eagle death and the presence of this new plant were related.

But Wilde had to interview all potential suspects. She started by sampling the lake’s water and sediment for bacteria. She arrived empty-handed. But when she began to examine the leaves of the hydrilla plant, she found colonies of previously unknown cyanobacteria. She named him Aetokthonos hydrillicola, “The eagle killer that grows on hydrilla.”