The world’s most widely used insecticides could be contributing to a decline in migratory bird populations and significant bird weight loss, a new study shows.
A Sep. 13 study published in the journal Science is the first experiment to track the effects of a neonicotinoid pesticide on birds in the wild.
“75% of North American farmland birds are seeing population declines, sparrows in particular,” said Christy Morrissey, a professor of Biology at the University of Saskatchewan, and a co-author of the paper.
The study found that sparrows who consumed small, field-realistic doses of neonicotinoid-coated seeds lost weight and suffered delays to their migration—which in turn could severely harm the birds’ ability to reproduce.
Neonicotinoids are the world’s most widely used class of insecticides. They are typically applied as a coating directly on seeds, such as corn, soybeans, and cereal crops.
Banned in EU
In recent years scientists have found that “neonics” also have contributed heavily to declines in insects and bee populations, including several species of bumble bees.
Those risks to commercial and wild pollinators led the European Union in 2018 to ban three of five neonic compounds.
A 2018 report from the European Food Safety Authority (EFSA) found the risk to bees varied by species and exposure route, but “taken as a whole the conclusions confirm that neonicotinoids pose a risk to bees.”
Morrissey said researchers have hypothesized for some time that exposure to neonics was playing a role in declines in farmbird populations, because birds were eating the coated seeds.
To test their theory they captured white-crowned sparrows migrating from the Arctic to the southern U.S.
They then exposed the birds to doses of imidacloprid—a common neonicotinoid seed coating—equivalent to 0.1 of a seed of corn seed, 0.2 of a soybean, 3-4 canola seeds, or 10 cereal seeds.
Within hours, Morrissey said, birds with the highest pesticide dose lost six percent of their body weight.
“That doesn’t sound like much, but in a 27-gram songbird, even a six percent loss in fat can have a big impact on the fuel for migrating,” she said.
The data showed the exposed birds stayed 3.5 days longer at the stopover sites, on average, because they needed more time to replenish fat stores.
Delays mean later arrivals at breeding grounds, “which decreases the chances those birds will be successful at breeding, and the overall chance of survival is reduced,” she said.
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