Secret behind the sudden mass death of bald eagles 27 years ago finally explained


Scientists had spent decades figuring out what caused the massive deaths of bald eagles in the southeastern US long ago, only recently when new research identified the disease that has seriously affected the birds for the past 27 years.

The Bald Eagle (Haliaeetus leucocephalus) known as birds of prey, suffered from an illness that made them physically impaired as early as 1994. She had become widespread in the eagle population, what to unprecedented high number of deaths.

For decades, despite continuous expert efforts, the deadly disease had not been identified, but a new study has linked it to a neurological disease caused by ingestion of a toxin produced by a species of cyanobacteria. The disease caused the eagles to starve or drown due to poor coordination when walking, swimming, and flying.

Similar impairments occurred to waterfowl and other birds of prey in six states in 1998.

Exposure of the eagle murders

(Photo: Photo by Alexas_Fotos on Unsplash)

Researchers at the US Environmental Protection Agency (EPA) worked with academic researchers to identify the disease called avian vacuolar myelinopathy (AVM).

The appearance of AVM was common in freshwater reservoirs in the southeastern United States., but its origin was unknown until scientists began looking into environmental conditions in AVM-positive waters.

Field tests and laboratory tests at several water sources showed that AVM-infected birds have ingested a neurotoxin produced by a species of cyanobacteria that lives on invasive aquatic plants. This species was later identified as Aetokthonoshydrillicola which has been shown to only grow on the invasive plant Hydrilla verticillata.

Scientists later discovered bromine, an unusual characteristic of the toxic bacteria and an indicator of pollution. Bromine is usually incorporated into man-made products like pesticides, dyes, gasoline, and plastic enclosures for electronics, which made it very rare to find it in cyanobacteria.

This led to the speculation that toxins are produced due to bromine-based herbicides used by sea managers to control the invasive weeds. H. verticillata.

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How algal blooms affect environmental health

How bromine gets into lakes remains a mystery to the team, as AVM-positive sites typically occur in man-made bodies of water. To fully understand the toxic production of cyanobacteria, the uptake of bromotoxin in the bodies of infected birds was also considered. They found that the toxin absorbed through the intestines accumulates in the body.

It then turned out that the toxins also affected fish, frogs, insects and worms. Because of this widespread ailment, AVM is now called vacuolar myelinopathy (VM).

“We still have to study how the toxin affects mammals and other organisms in food chains to understand how it accumulates in various food webs,” said EPA scientist Matt Henderson.

The results suggest that cyanobacteria are “potentially dangerous toxin producers” and harmful to ecosystems and the environment. It is also important to network with marine managers to raise awareness of the dangers of bromine-based chemicals and offer alternative management solutions that are environmentally friendly.

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