Mysterious Kenya Flamingo Die-Offs Tied to Toxins, Stud

Sharon Guynup
for National Geographic Today

November 8, 2002

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.

Mass Die-Offs

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.

Food Contamination

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 birds—behavior 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.

Heavy Pollution

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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