Study shows popular insecticides harm birds in the United States

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The increased use of neonicotinoid pesticides in the continental United States may have impacted bird populations and reduced bird diversity, according to a paper published this week in Nature Sustainability.

Bird biodiversity is declining at a marked rate. Bird populations in the United States have decreased by 29 per cent since 1970, which has been attributed to various factors including the increased use of pesticides in agricultural production.

Nicotine-based pesticides - known as neonicotinoids - have been used increasingly in the United States over recent decades.

Previous research has shown that neonicotinoids are potentially toxic to birds and other non-target species. However, the impact of these pesticides on bird diversity in the United States is unclear.

Madhu Khanna and colleagues studied the effects of neonicotinoids on birds in the United States from 2008–2014.

They analysed data from the North American Breeding Bird Survey to identify county-level changes for four different bird species groups — grassland birds, non-grassland birds, insectivorous birds and non-insectivorous birds — and combined this with county-level data on pesticide use.

The authors found that an increase of 100 kg in neonicotinoid usage per county, a 12 per cent increase on average, contributes to a 2.2 per cent decline in populations of grassland birds and 1.6 per cent in insectivorous birds.

By comparison, the use of 100 kg of non-neonicotinoid pesticides was associated with a 0.05 per cent decrease in grassland birds and a 0.03 per cent decline in non-grassland birds, insectivorous birds and non-insectivorous birds.

Since impacts accumulate, the authors also estimate that, for example, 100 kg neonicotinoid use per county in 2008 reduced cumulative grassland-bird populations by 9.7 per cent by 2014.

These findings suggest that neonicotinoid use has a relatively large effect on population declines of important birds and that these impacts grow over time.

The authors also found that the adverse impacts on bird populations were concentrated in the Midwest, Southern California and Northern Great Plains.