What Killed These Bald Eagles? After 25 Years, We Finally Know.

Wilde and her colleagues knew they needed to identify the toxin itself. In 2011, she sent samples to Timo Niedermeyer, a biochemist now at the Martin Luther University of Halle-Wittenberg, in Germany, who specializes in molecules made by cyanobacteria. He and his colleagues tried to grow the species in his lab, but it grew incredibly slowly. It took two years to produce less than an ounce, which he sent back to Georgia to test in chickens. The cyanobacteria so painstakingly cultivated had no effect at all. No lesions. No clumsy behavior. “We spent two years and achieved nothing,” Niedermeyer says.

The team wondered if lab-cultivated cyanobacteria were somehow different from wild ones. But how? Niedermeyer went back to samples collected in the lakes, using a sophisticated technique called AP-MALDI-MSI—“like taking a picture but you don’t detect light but molecules,” he says—which revealed a novel molecule found only in the cyanobacteria growing on the hydrilla. The lab-grown cyanobacteria did not have it, nor did hydrilla by itself.

What’s more, this molecule had a formula never seen before, and, unusually, it contained five atoms of the element bromine. So the team tried adding bromine to its growing cyanobacteria. Lo and behold, the same strange molecule appeared, and this new batch of cyanobacteria caused the brain lesions in chickens. Another group of collaborators confirmed the team’s work further, by finding the cyanobacteria genes likely responsible for synthesizing the toxin. The team ultimately named this toxin aetokthonotoxin, “poison that kills the eagle.” Twenty-five years later, it finally had a name.

“I just have a lot of admiration that the scientists kept plugging away at this,” says Meteyer, the pathologist who helped identify AVM. Over the years, when asked about the frustrating parts of her career, she’s pointed to AVM as one of them.

Yet there are still more puzzles to solve. Where is the cyanobacteria getting the bromine? The element is relatively rare in fresh water, but Wilde says that hydrilla seems to sequester it. The concentration in the plant is 300 times higher than in the water column. How bromine is getting into the lakes in the first place is another mystery; the study authors suggest that it could be from coal plants that use bromine to remove mercury or, ironically, from herbicides used to kill the invasive hydrilla.

The key to preventing bird deaths from AVM might be simply weeding out hydrilla. The conditions that led to the original eagle deaths—a man-made lake, an invasive plant, bromine pollution—were an accidental confluence of many human choices that engineered the environment. Remaking the world for bald eagles means engineering their habitats again, but deliberately. One strategy, Wilde said, is stocking lakes with sterile grass carp, which are “shocked” with changes in temperature or pressure in the egg stage to give them an extra chromosome. These carp live several years and eat the hydrilla, but are unable to reproduce. (Lab studies on whether the toxin affects the fish have been contradictory.)

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