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Several studies over the past few years have linked pesiticides called neonicotinoids to Colony Collapse Disorder (CCD), the disease causing large honeybee die-offs in the United States and Europe. Now, a new European study points the finger at neonics, as they’re called, for bird declines as well.

A team of Dutch researchers compared data from two long-term monitoring programs in the Netherlands—bird populations and environmental water quality—for the years 2003-2009. The scientists specifically selected 15 species of insect-eating farmland birds and tested whether imidacloprid, the most commonly used neonicotinoid compound, is affecting the abundance of these birds.

The team discovered that, sure enough, bird population declines were strongly correlated with the concentration of imidacloprid in the water. According to the study, published last month in Nature,

At imidacloprid concentrations of more than 20 nanograms per litre, bird populations tended to decline by 3.5 percent on average annually. Additional analyses revealed that this spatial pattern of decline appeared only after the introduction of imidacloprid to the Netherlands, in the mid-1990s.

The scientists link the bird decline to lack of food. Insects constitute a substantial part of the diet of many bird species during the breeding season and are important for raising offspring. Nine of the 15 species investigated exclusively eat insects, and all species feed insects to their young, which supports the theory that pesticide use is negatively impacting bird populations through depletion of their food sources.

However, the scientists don’t rule out the possibility that the birds could be ingesting the pesticide directly—either through their insect meals or eating seeds coated with imidacloprid, either of which could kill the birds. The study authors suggest that not only do we have more to learn on the effects of this pesticide, but that “Future legislation should take into account the potential cascading effects of neonicotinoids on ecosystems.” The European Union currently has a two-year moratorium on neonics, and last week the U.S. Fish and Wildlife Service placed a ban on the pesticide in National Wildlife Refuges. Small steps to fight a potentially big issue…

Image: Jouke Altenburg, Radboud University

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