This deadly toxin may be the reason behind mysterious eagle deaths

Published: April 12, 2021

sick-eagle-perched-in-swampy-lake Photo by Diane Isabel/Shutterstock

It was the largest undiagnosed die-off of bald eagles in U.S. history. Over two winters in the 1990s, almost 60 eagles were found dead or fatally ill around an Arkansas lake. Some were paralyzed. Others tried to fly but crashed into trees. When autopsied, their brains were riddled with tiny Swiss-cheese holes, or “vacuoles.” 

Since then Vacuolar Myelinopathy, as the new disease is called, has triggered sporadic outbreaks in eagles, ducks, coots, and Canada Geese in six southeastern states. But its cause remained a mystery until last month, when scientists from the U.S., Germany and the Czech Republic fingered four suspects, including the ringleader, a cyanobacteria that’s a distant cousin of the same algae-like creatures that slime Canadian cottage lakes.

Instead of floating in the water like the cyanobacteria cottagers most familiar with, Aetokthonos hydrillicola hitchhikes on Hydrilla, an invasive aquatic plant. When there’s enough bromine in the water — possibly from aquatic herbicides, coal-fired power plants, fire retardants or even road salt — the cyanobacteria forms a powerful brain toxin.

“This is incredible detective and forensic work,” says University of Ottawa biology professor and cyanobacteria researcher Frances Pick. “The compound responsible for the eagle deaths is a brand new cyanotoxin, very different from other neurotoxic cyanotoxins we have known about.”

Pick adds there’s a lot more to learn about the toxin and its link with bromine. But the good news is limiting bromine pollution and stopping Hydrilla — an escaped aquarium plant that has been working its way north since the 1950s — could keep the disease out of Canada. 

“Hydrilla’s not in the Great Lakes yet, but it’s in tributaries in New York State,” says Invasive Species Centre analyst Colin Cassin. “The onus is on us to be on the lookout. We still have the opportunity to prevent Hydrilla from becoming established.”

“This story should serve as a wake-up call to those who don’t take the spread of aquatic invasive species seriously,” adds Alberta Environment and Parks aquatic scientist Ron Zurawell. “People need to regard cyanobacteria as true bacteria, and not simply a harmless form of algae. These organisms are capable of producing myriad compounds, some of which are capable of severe harm to humans, pets, livestock, wildlife, and even plants.”

“Cyanobacteria should not be underestimated. Period.”

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