Toxicologists studying white-crowned sparrows have shown that these birds become anorexic after eating neonicotinoid pesticide-laced seeds, causing them to lose weight and delay their southward journeys. The study might apply to other birds as well—and help explain the dramatic songbird decline of recent decades, researchers say.
Neonicotinoids are the world’s most widely used class of pesticide. They protect seeds—and the plants that grow from them—from insects resistant to other pesticides. But scientists have recently found that they can decimate pollinators like honey bees and bumble bees.
Laboratory studies have shown that neonicotinoids sicken and disorient captive birds, but no data existed on how they affect wild birds, who often swoop into fields to nosh on pesticide-laced seeds.
Researchers wondered whether pesticide exposure might explain a massive recent decline in farmland bird species. The researchers caught dozens of white-crowned sparrows (Zonotrichia leucophrys) in southern Ontario province in Canada as the birds migrated from the Arctic to the southern United States. They kept the birds in cages with food and water for 6 hours. About a dozen received low doses of the neonicotinoid imidacloprid—equivalent to what they might ingest had they eaten several seeds from a recently planted field. Another dozen got a lower dose of the pesticide, and control birds received the same handling but no pesticide. After 6 hours, the researchers put a tiny radio transmitter on each bird’s back and released it into a 100,000-square-kilometer site in Ontario, where 93 regularly spaced radio towers track tagged animals.
Within hours, birds with the highest pesticide dose lost an average of 6% of their body weight and about 17% of their fat stores, which are key to fueling long flights. Over the course of those 6 hours, the birds given pesticides stopped eating, taking in about one-third the food that untreated birds ate, they note.
Nor did the birds recover quickly when released. Half of the high-dose birds stuck around Ontario an extra 3.5 days or longer. Researchers think the birds needed that extra time to get the pesticide out of their systems, start to eat again, and regain their lost fat.
The research provides “a compelling set of observations” that shows how even low doses of neonicotinoids can affect bird survival and reproduction. These effects could help explain declines in sparrow populations—and may apply to other birds.
Politics, Corporate Profit & Lobbying Harming Wildlife
These pesticides can decimate pollinators like honey bees and bumble bees. And concerns about their harm to wildlife led the European Union to ban three of these compounds in 2018. But few researchers think the United States or Canada will have the political will to ban neonicotinoids despite the harm occurring to wildlife, because the pesticides are protective for food crops and are the focus of corporate profits and rigorous lobbying efforts.
Some researchers argue that rather than treat all seeds before they are planted, farmers could save money and reduce birds’ exposure by applying the pesticide to plants only after an insect outbreak occurs.
It has also been suggested that researchers explore other methods to reduce birds’ exposure, including coming up with better ways to bury seeds—and remove those that spill—during planting.
Journal Reference: Margaret L. Eng, Bridget J. M. Stutchbury, & Christy A. Morrissey, A neonicotinoid insecticide reduces fueling and delays migration in songbirds, Science 13 Sep 2019: Vol. 365, Issue 6458, pp. 1177-1180. DOI: 10.1126/science.aaw9419