The increasing use of neonicotinoid insecticides is a major factor in the decline of grassland birds in the United States, according to a new study published in Nature Sustainability.
Numerous studies have shown neonicotinoids — nicotine-based pesticides — negatively affecting wild bees, honeybees, and butterflies, but large-scale studies on the pesticide’s impact on birds have been limited, says Madhu Khanna, distinguished professor in agricultural and consumer economics at the University of Illinois and co-author on the paper.
“This represents the first study at a national scale, over a seven-year time period, using data from hundreds of bird species in four different categories – grassland birds, non-grassland birds, insectivores, and non-insectivores,” she says.
“We found robust evidence of the negative impact of neonicotinoids, in particular on grassland birds, and to some extent on insectivore birds after controlling for the effects of changes in land use.”
Khanna and co-authors Yijia Li, a graduate student at Illinois, and Ruiqing Miao, assistant professor at Auburn University, analyzed bird populations from 2008 to 2014 in relation to changes in pesticide use and agricultural crop acreage.
The authors found that an increase of 100 kilograms in neonicotinoid usage per county — a 12% increase on average — contributed to a 2.2% decline in populations of grassland birds and 1.6% in insectivorous birds. By comparison, the use of 100 kilograms of non-neonicotinoid pesticides was associated with a 0.05% decrease in grassland birds and a 0.03% decline in non-grassland birds, insectivorous birds, and non-insectivorous birds.
Since impacts accumulate, the authors estimate that, for example, 100 kilograms of neonicotinoid use per county in 2008 reduced cumulative grassland-bird populations by 9.7% 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.
According to the study, the adverse impacts on bird populations were concentrated in the Midwest, Southern California, and the northern Great Plains.
The researchers say the effect of neonicotinoids could result directly from birds consuming treated crop seeds, and indirectly by affecting the insect populations they feed on. Consumption of just a few seeds is enough to cause long-term damage to the birds’ reproduction and development.
The study included data on bird population and species diversity from the North American Breeding Bird Survey, a comprehensive database with data from about 3,000 bird routes across the United States. The researchers correlated the bird data with pesticide use, as well as satellite data on agricultural crop acreage and urban land use.
Impacts build over time
I asked Khanna what, if anything, surprised her about the research.
“We were surprised by two things. One was the significantly larger negative impact of neonics on bird biodiversity compared to that of conventional pesticides and compared to the effects of land use,” she says. “Previously there has been mixed evidence on whether it is lack of habitat (due to expansion of cropland) or management practices (like pesticides) that affect bird populations.
“We also found that the effect of neonics persists over time. Neonics affect birds that consume them and by reducing bird populations, they reduce the capacity to reproduce in the future. We found that the effects of applying neonics today had negative effects that lasted for several years.”
The authors conclude their paper by writing: “This research provides compelling support for the re-evaluation of policies permitting the use of neonicotinoids by the U.S. Environmental Protection Agency by incorporating considerations of the implications of these pesticides for bird habitats.”
I asked Khanna if a ban on neonics would be necessary to help bird populations recover.
“Our results do indicate that reducing neonic use will help bird populations to recover but whether a ban is the appropriate policy or a more targeted reduction is preferable remains to be examined,” she says.
Meanwhile, she adds, birdwatchers “can use the findings of this study to make the case for more research on the effects of neonics on particular species, the safer alternatives to neonics, and the appropriate regulations to reduce the negative effects of neonics on birds and other organisms. They can also make a case for continuing to provide data on neonics to the public.”
Previous coverage of neonics: