The Leibniz-Institut team presented its findings at the recent International Conference on Harmful Algae in St. Petersburg, Florida.
Leibniz researchers visited Rift Valley lakes four times over the past year. "We saw a lot of dying birds," said biologist Andreas Ballot. "There were a few hundred, staggering around in slow motion, their necks bent backward. It took them about half an hour to die."
This is one of the first known incidents in which "filter-feeding" birds are being killed by contamination of their food source, Ballot added.
Because of how they feed, flamingos are particularly vulnerable to pollutants. Wading in the lake shallows, they stir up organic matter with their bills, including mollusks and crustaceans and the bird's favorite meal, spirulina, a type of nontoxic blue-green algae.
The birds hold their bills upside down, using their lower bills and tongues to pump water through fringes on the top bills, which filters out microscopic mouthfuls of food.
Val Beasley, a toxicologist with the Envirovet Program and a professor at the University of Illinois Urbana at Champaign, has also witnessed signs of neurological impairment in dying birdsbehavior consistent with neurotoxic poisoning.
But only additional research can help scientists reach a definite conclusion. "It's possible that more than one thing is happening," Beasley said.
Water levels in the Rift Valley lakes have fluctuated greatly over the past few years, alternately increasing the frequency of algal blooms or making food scarce.
Lake Nakuru nearly dried up several times during the 1990s. But in 1997, the region was inundated with El Niño rains, which lowered the salinity of lake waters. It decimated the flamingos' food supply, and their long flights to find nourishment caused further stress, said Motelin.
But human activity is also to blame.
Lake Nakuru has become highly polluted since 1975, when the nearby city of Nakuru began heavy industrialization; heavy metals and other toxic substances accumulated in the water and sediment. Fertilizer and pesticide runoff from the valley's increasing number of farms has added nutrients that contribute to the growth of algal blooms.
"This is a sensitive topic because it's not good for tourism," said ecotoxicologist Stephan Pflugmacher of the Leibniz-Institut. "It puts pressures on the government to look after their lakes."
A Kenyan environmental agency, the Pollutant Release and Transfer Registers, is now working with 16 industries to help them meet cleanup standards.
"We are concerned because this could be a catastrophe," said Motelin. "The combination of poisons could cause death, as they affect different sensitive organs of the body. If we are going to arrest the situation, pollution has to stop."
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