The number of migratory songbirds returning to North America has gone into sharp decline due to the unregulated use of highly toxic pesticides and other chemicals across Latin America.
Ornithologists blame the demand for out-of-season fruit and vegetables and other crops in North America and Europe for the destruction of tens of millions of passerine birds. By some counts, half of the songbirds that warbled across America's skies only 40 years ago have gone, wiped out by pesticides or loss of habitat.
Forty-six years ago, the naturalist Rachel Carson wrote Silent Spring, a study of the ravages caused to wildlife, especially birds, by DDT. The chemical's use on American farms almost eradicated entire species, including the peregrine falcon and bald eagle.
The pesticide was banned and bird numbers recovered, but new and highly toxic pesticides banned by the US and European Union are being widely used in Latin America.
Because of changed consumer habits in Europe and the US, export-led agriculture has transformed the wintering grounds of birds into intensive farming operations producing grapes, melons and bananas as well as rice for export.
Ornithologists say another silent spring is dawning across the US as birds are being poisoned by toxic chemicals or killed as pests in their winter refuges across South and Central America as well as the Caribbean. They say that many species of songbird will never recover, and others may even become endangered or extinct if controls are not put in place or consumer habits changed.
More problems await those birds which make it home. Millions of acres of wilderness the birds use as nesting grounds have been ploughed under in the drive to grow corn for ethanol, for bio-fuel.
Some 150 species of songbirds undertake extraordinary migrations up to 12,000 miles every year as they move from the south to nesting grounds in the US and Canada every spring. Ornithologists say that almost all these species are at risk of poisoning.
The migratory songbirds in most trouble include the wood thrush, the Kentucky warbler, the eastern kingbird and the bobolink, celebrated by the 19th century American poet Emily Dickinson as "the rowdy of the meadows".
Bridget Stutchbury, an ornithologist and professor at York University in Toronto, said: "With spring we take it for granted that the sound of the songbirds will fill the air with their cheerful sounds. But each year, as we continue to demand out-of-season fruits and vegetables, fewer and fewer songbirds will return."
The bobolink songbird has experienced such a steep decline, it has almost fallen off the charts. The birds migrate in flocks from Argentina, Bolivia and Paraguay to the east coast of the US, feeding on grain and rice, prompting farmers to regard them as a pest. Bobolink numbers have plummeted almost 50 per cent in the past four decades, according to the North American Breeding Bird Survey.
Rosalind Renfrew, a biologist who studied bobolinks as they were feeding in rice paddies in Bolivia, found about half of the birds had been exposed to toxic chemicals banned in Europe and the US. Some 40 to 50 species, which include the barn swallow, the wood thrush the dickcissel as well as migratory birds of prey, are starting to disappear.
It is only recently that the decline has been definitively linked to the use of toxic pesticides in the Caribbean and across Latin America. "Everyone who has looked for pesticide poisoning in birds has found it," Professor Stutchbury said. "When we count birds during our summers we are finding significant population declines in about three dozen species of songbirds."
She wrote in the comment pages of The New York Times: "They are the modern-day canaries in the coal mine." She said: "The imported fruits and vegetables found in our shopping carts in winter and early spring are grown with types and amounts of pesticides that would often be illegal in the United States."
Growers are using high doses of pesticides, which the World Health Organisation calls class I toxins. These are also toxic to humans and are either restricted or banned in the US and EU. But controls in Latin American countries are easily flouted.
"I believe that if we don't make drastic changes quite literally many birds which are common now are going to become rare," said Professor Stutchbury.
Testing by individual EU countries and the US Food and Drug Administration reveals that fruits and vegetables imported from Latin America are three and sometimes four times as likely to violate basic standards for pesticide residues.
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