THE sight of millions of flamboyant pink Lesser Flamingos congregating on the lakes of East Africa is one of the most impressive in nature. But every few years, a mysterious killer wipes out thousands of the birds, and leaves their corpses littering the shorelines.
Pollution and infectious diseases have been fingered as potential culprits. But researchers say they have a new suspect. While it is too early to close the case just yet, they say there is strong evidence that the birds are being poisoned by a naturally occurring toxic cyanobacterium.
Two years ago, up to 50,000 birds died inexplicably at Lake Bogoria in Kenya, and in 1995 thousands of flamingos also dropped dead at Lake Nakuru. Heavy-metal poisoning was blamed at the time of the last outbreak but experts are sceptical.
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It鈥檚 yet another pressure on the species. Despite their apparent abundance, the birds鈥� natural habitat is dwindling and they are close to being listed as threatened.
Now Geoffrey Codd, a microbiologist at the University of Dundee, says it is likely that the flamingos were poisoned by their food. A Lesser Flamingo eats with its head upside down and underwater, filtering bacteria through its bill. Usually they feast on a particular species of cyanobacteria called Arthrospira fusiformis. But samples from Lake Bogoria revealed two further species of cyanobacteria, Anabaena and Anabaenopsis, which produce toxins that can kill cattle, sheep and water birds. If the flamingos had been eating the toxic species, it would explain why they had died.
Lothar Krienitz of the Leibniz-Institute of Freshwater Ecology and Inland Fisheries in Berlin first raised the alarm. After visiting the lake to observe the dead and dying birds, he contacted Codd earlier this year. Krienitz had recognised the symptoms of poisoning by cyanotoxins: the affected flamingos staggered and convulsed before dying with their necks snapped backwards.
Krienitz had collected tissue samples from the dead birds in 2000, which he sent to his colleague Stephan Pflugmacher in Berlin and to Codd for tests. Both found that the tissues contained cyanotoxins at concentrations high enough to have killed a flamingo.
The researchers gathered at the 10th International Conference on Harmful Algae in St Pete Beach in Florida last month to present the evidence. They say populations of cyanobacteria in the lake must now be closely studied to see if the toxic species flourish at the same time as the Lesser Flamingos perish.
Ecologist David Harper of the University of Leicester, who leads Earthwatch expeditions to Lake Bogoria four times a year, is negotiating to get funding for Kenyan scientists to monitor the lake each month to determine if, and why, the balance of bacterial species changes. The Earthwatch teams will also check whether the birds are suffering from avian tuberculosis, an endemic disease in flamingos that could flare up and cause widespread death in a population already weakened by environmental stress.