A new study has linked neonicotinoids, the best-selling insecticides in the world, to declining populations of insect-eating birds.

Researchers in the Netherlands combed through the results of years of local water-quality measurements and breeding-bird surveys and then compared concentrations of imidacloprid, the most widely used neonicotinoid, with population trends for 15 Old World songbirds that either depend on insects during the breeding season or eat nothing but insects year-round.

The results, write the investigators, “suggest that the impact of neonicotinoids on the natural environment is even more substantial than has recently been reported and is reminiscent of the effects of persistent insecticides in the past.”

Fourteen of the 15 species — including Eurasian Skylark, Barn Swallow, Yellow Wagtail (pictured above), Common (European) Starling, Common Whitethroat, and Mistle Thrush — had a negative response to the imidacloprid concentrations.

The surface-water concentration above which bird populations declined was only 19.43 nanograms per liter. In areas where measured concentrations were above this threshold, the researchers report, populations fell an average of 3.5 percent annually.

“So far, the suggested potential risks of neonicotinoids for birds have focused on the acute toxic effects caused by direct consumption,” write the researchers in the journal Nature. “Our results suggest another possibility: that is, that the depletion of insect food resources has caused the observed relationships.”

Direct effects on birds were described in a report released last year by American Bird Conservancy: It claimed that a single kernel of corn coated with a neonicotinoid was enough to kill a songbird.

Read the ABC report: The Impact of the Nation’s Most Widely Used Insecticides on Birds (PDF).

Citing “high acute risks” for bees and other pollinators, the European Union suspended the use of imidacloprid and two other neonicotinoids for two years. The suspension began at the end of 2013.

The U.S. Fish and Wildlife Service followed suit in July, announcing that it would phase out the use of neonicotinoid pesticides throughout the 150 million-acre National Wildlife Refuge System by January 2016.

USFWS had earlier announced that it would phase out all neonicotinoids in refuges in the Pacific Region, including Hawaii and other Pacific islands, Idaho, Oregon, and Washington, by January 2016.

Health Canada’s Pest Management Regulatory Agency and the U.S. Environmental Protection Agency are conducting regulatory reviews of neonicotinoids.

A version of this story appeared in the October 2014 issue of BirdWatching magazine. Subscribe.

Read the abstract Caspar A. Hallmann, Ruud P. B. Foppen, Chris A. M. van Turnhout, Hans de Kroon, and Eelke Jongejans (2014) Declines in insectivorous birds are associated with high neonicotinoid concentrations. Nature 511, 341–343 (17 July 2014). Abstract.

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Originally Published