Neonics—pesticides introduced to plants at the seed stage—act like an appetite suppressant for birds, making them lose weight within hours.
The world’s most widely used insecticide has been linked to the dramatic decline in songbirds in North America. A first ever study of birds in the wild found that a migrating songbird that ate the equivalent of one or two seeds treated with a neonicotinoid insecticide suffered immediate weight loss, forcing it to delay its journey.
Although the birds recovered, the delay could severely harm their chances of surviving and reproducing, say the Canadian researchers whose study is published today in Science.
“We show a clear link between neonicotinoid exposure at real-world levels and an impact on birds,” says lead author Margaret Eng, a post-doctoral fellow at the University of Saskatchewan Toxicology Center.
Spring bird migration occurs when farmers are planting, and most crops in the United States and Canada are grown with neonicotinoid-treated seeds. Birds may suffer repeated exposure at successive stopover sites where they rest and feed. That may extend migration delays and their consequences, the study concludes.
Neonicotinoids, introduced in the late 1980s, were supposed to be a safer alternative to previous insecticides. But study after study has found that they play a key role in insect decline, especially bees. The EU banned the use of the chemicals in 2018 because they were killing pollinators. This study is another link in the chain of environmental problems, one showing that the use of neonicotinoids is harming birds, and that bird populations are at risk as a result, Eng said in an interview.
It’s the first proof of “behavioral effects in free-living birds as result of neonicotinoid intoxication,” says Caspar Hallmann, an ecologist at Radboud University in the Netherlands.
treated grains, said Hallmann, who was not involved in the Science study. Hallman’s own published research has linked widespread declines in insect-eating birds to neonicotinoid use.
The populations of more than 75 percent of songbirds and other birds that rely on agricultural habitat in North America have significantly declined since 1966. The new study reveals how neonicotinoids, also known as neonics, could be directly contributing to the die-offs. Just last month a comprehensive study concluded that the widespread use of neonicotinoids had made America’s agricultural landscape 48 times more toxic to honeybees, and likely other insects, than it was 25 years ago.
To investigate the potential impacts on wild birds, researchers captured white-throated sparrows during a stopover on their spring migratory route from the U.S. to the boreal region of Canada, which spans the top of the country. Individual sparrows were fed either one very small dose of the most commonly used neonicotinoid, called imidacloprid, or a slightly higher dose, or one with no insecticide.