A class of pesticides widely blamed for a worldwide collapse in pollinator populations is also devastating populations of birds, according to a new study conducted by researchers from Radboud University in the Netherlands and the Centre for Field Ornithology and Birdlife Netherlands, and published in the journal Nature on July 16.
The chemicals, known as neonicotinoids, have increasingly come under fire for widespread destruction of organisms other than agricultural pests.
"I think we are the first to show that this insecticide may have wide-scale, significant effects on our environment," researcher Hans de Kroon said.
In the past 20 years, neonicotinoids have become one of the fastest-growing pesticide classes. In contrast to most other pesticides, which must be sprayed directly onto plants close to the time that insect extermination is desired, neonicotinoids are simply used to treat seeds before planting. As a treated plant grows, it absorbs the poison into every single one of its tissues, making the entire plant toxic.
That means that even the plant's flowers, nectar and pollen become deadly, killing pollinators that visit the crop.
"The plants become poison not only for the insects that farmers are targeting, but also for beneficial insects like bees," said Jennifer Sass, a senior scientist with the Natural Resources Defense Council.
In addition, the neonicotinoids can spread into the surrounding soil and persist for years, thereby contaminating future generations of plants - including non-agricultural species.
"So they actually end up in plants that grow on the sides of fields that were never meant to be targeted," Sass said.
Due to concerns over their effects on pollinators, several varieties of neonicotinoid (including imidacloprid, the variety examined in the Nature study), have been banned in many European countries.
A new "silent spring"
The Dutch researchers compared long-term data on chemical concentrations in surface water and on farmland bird populations in several areas of the country. They found that in the areas with the highest imidacloprid contamination, populations of 14 separate bird species declined by an average of 3.5 percent every year. The researchers also looked for a correlation between bird populations and other possible risk factors - such as urbanization of farmland, fertilizer use, or changes in crops planted - but only neonicotinoid concentration was associated with the population drop.
The pesticides may be killing birds in two separate ways, the researchers suggested. First, birds could be eating parts of the contaminated plants, particularly seeds; according to a 1992 study by the U.S. Environmental Protection Agency (EPA), sparrows that ate neonicotinoid-treated seeds lost the ability to fly and became immobile. Secondly, neonicotinoids might be destroying the food base of birds that feed on insects and other invertebrates.
The latter explanation is supported by the recent findings of the Task Force on Systemic Pesticides, a multidisciplinary group of 29 scientists that reviewed 800 separate studies on neonicotinoids and wildlife. The task force found that neonicotinoids were killing off not just agricultural pests but also insects, earthworms, aquatic invertebrates, and even fish and lizards. These effects happened even when the products were used according to manufacturer guidelines.
Neonicotinoid use, the task force wrote, is "likely to have a wide range of negative biological and ecological impacts."
Dutch researcher Ruud Foppen said he sees a parallel between the new study and the seminal 1962 environmental book Silent Spring, by Rachel Carson. Carson's book, which is viewed as highly influential in launching the modern environmental movement, warned that organophosphate pesticides such as DDT were devastating bird populations.
"In this way, we can compare it to what happened decades ago," Foppen said. "And if you look at it from that side, we didn't learn our lessons."
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