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Halle / Georgia (dpa) - German researchers have solved the mystery of the mysterious death of bald eagles in the south-east of the United States with their forensic instinct.
The cause is a poison formed by blue-green algae, as a team led by Timo Niedermeyer from the University of Halle-Wittenberg and Susan Wilde from the University of Georgia writes in the journal Science.
Bald eagles are the heraldic animal of the USA.
With a wingspan of over two meters, they are among the largest birds of prey in North America.
The head, neck and tail feathers are white and contrast with the dark brown body feathers.
Bald eagles, but also other birds in the southeastern United States, have suffered from nerve disorders since the 1990s.
The animals lose control of their bodies and die.
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During her investigations, Susan Wilde first discovered that a substance from a previously unknown blue-green alga that lives on ground nettles (Hydrilla verticillata) in freshwater lakes made various birds and other animals sick.
According to their knowledge, the harmful substance found its way into herbivorous fish, water birds and turtles, which were eventually eaten by the bald eagles.
What exactly led to the poisoning of the blue-green algae, also known scientifically as cyanobacteria, was unclear.
At the University of Halle-Wittenberg, experts in cyanobacteria have now identified what is known as the “eagle killer poison”.
When Niedermeyer learned that Susan Wilde suspected cyanobacteria on the leaves of ground nettles to be the cause of the neurological disease in water birds, he had samples sent from Georgia.
He scraped the cyanobacteria off the plants and grew them in the laboratory.
Back in Georgia, tests were carried out to determine whether the bacteria actually poisoned the birds.
The cyanobacteria sent to Georgia from the laboratory in Germany did not make the birds sick.
“It wasn't just the birds that went mad, it was us too.
We wanted to find out, ”says Niedermeyer.
The bacteria grown were not poisonous.
Therefore, the researcher had new samples sent to him.
This time his team also analyzed the surface of the leaves.
A peculiar bromine compound was found on the leaves and it became clear that the bacteria need bromine to produce their bromine-containing poison.
It was only after bromine-containing salts were added to the laboratory cultures that the bacteria could make birds sick.
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Not only was the murderer caught, but his weapon was also discovered, said Wilde.
It is still unclear why the bacteria produce the poison in some lakes - but not in others.
The researchers suspect that a herbicide containing bromine is used in some lakes to destroy the invasive ground nettle.
But bromine compounds also occur in nature.
© dpa-infocom, dpa: 210326-99-979823 / 2