for National Geographic Today
Kenya's vast Lake Nakuru is dotted with noisy colonies of brilliant pink lesser flamingos, a sight mirrored at Lake Begoria and other lakes across the East African Rift Valley.
The region supports a population of about one million of the stately, stilt-legged creatures, the smallest of six flamingo species, along with 400 types of migratory birds. The splendid wildlife display draws international visitors to what ornithologists call "the most fabulous bird spectacle in the world."
But there's trouble in flamingo paradise. For nearly a decade, the birds have periodically perished in large numbers, leaving the shores of the lakes littered with mountains of pink bird carcasses.
The deaths have alarmed conservationists and triggered investigations, but the exact cause of the mysterious die-offs remains unknown. Recent bird counts suggest that African flamingo populations have declined by 20 percent over the past 20 years.
"Flamingos have been in existence for 50 million years, but if their numbers continue to decline by 20 percent every two decades, we may lose the entire African population within 100 years," said Ramesh Thampy, director of the World Wildlife Fund's Eastern Africa Regional Program in Nakuru.
The first mass die-off occurred in 1993, with an estimated 40,000 birds dying from August to November; two years later, some 20,000 perished. More mass deaths came in 1997, with smaller losses since. Apparently no other lake mammals or birds have been affected.
Pollution was a suspected cause, so researchers tested the dead birds for toxic substances. Analysis showed detectable levels of zinc, copper, lead, mercury, cadmium, selenium, chromium, iron, and arsenic in the birds' tissue.
"The presence of heavy metals in the bird tissues is alarming," said veterinary pathologist Gideon Motelin at Egerton University in Nakuru. The metals were found at levels that "threaten the very existence of the flamingos," he said.
A team of German and Scottish researchers identified an additional potential killer: a potent neurotoxin produced by a type of blue-green algae.
"We assume that this neurotoxin, anatoxin-a, is also contributing to the die-offs, as we found it in high concentrations," said Claudia Wiegand, an ecotoxicologist with the Leibniz-Institut of Freshwater Ecology and Inland Fisheries in Berlin. "The bird's detoxification capacity may be exhausted by overexposure to pesticides and heavy metals, allowing less toxic outbreaks to be lethal."
Flamingos can live for 50 years, allowing a steady, potentially deadly accumulation of toxins.
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