- In a new study, wild white-crowned sparrows that were exposed to seeds treated with imidacloprid, a neonicotinoid insecticide, suffered considerable weight loss and delayed the timing of their migration.
- The delayed migration could in turn be affecting the birds’ survival and reproduction, the researchers say.
- The findings suggest that neonicotinoids could have partly contributed to the decline of several farmland-dependent bird species in North America as seen in the past few decades, the researchers add.
A popular group of pesticides linked to huge declines in bees around the globe could be adversely affecting migratory birds making pit stops on farmlands, according to new research.
In the study, wild white-crowned sparrows (Zonotrichia leucophrys) exposed to seeds treated with imidacloprid, a neonicotinoid insecticide, suffered considerable weight loss and delayed the timing of their migration. The delayed migration could in turn be affecting the birds’ survival and reproduction, the researchers say.
For a long time, the toxic effects of neonicotinoids, which are often applied to seeds as a coating, were thought to be limited to insects. But there is growing evidence the chemicals may be affecting birds as well.
Margaret Eng, a postdoctoral fellow at the University of Saskatchewan, and colleagues had previously showed that exposing captive white-crowned sparrows to imidacloprid caused dramatic declines in their weight and fat stores and disoriented the birds. Now, for the first time, the researchers have demonstrated the effects of the pesticides in wild birds.
In the spring of 2017, the team caught 36 white-crowned sparrows at a stopover site in Ontario, Canada, during the birds’ migration from the U.S. to Canada’s boreal region. The birds, temporarily held in cages before release, were randomly assigned to three treatment groups: one group of 12 birds was fed seeds with a low dose of imidacloprid, a second group of 12 birds was fed seeds with a slightly higher, but sub-lethal, dose of imidacloprid, and the third group of 12 birds was given untreated seeds with no pesticides at all. The researchers measured each bird’s weight and body composition before and after exposure, and attached a lightweight radio transmitter to the bird’s back to track them after releasing them into the wild.
Birds that ate the insecticide-free seeds did not lose much weight when weighed six hours after they were fed. Those fed on seeds with lower dose of the pesticide, however, had lost around 3 percent of their body weight and 9 percent of body fat, while those that were exposed to the higher dosage lost 6 percent of their body weight and 17 percent of body fat on average.
The effects of the pesticides seemed to linger after the birds were released. While the birds eventually recovered, those that had been exposed to higher doses of imidacloprid stayed about 3.5 days longer at the stopover site after release before continuing on their migratory path compared to birds that were given untreated seeds.
“Both of these results seem to be associated with the appetite suppression effect of imidacloprid,” Eng, lead author of the study, said in a statement. “The dosed birds ate less food, and it’s likely that they delayed their flight because they needed more time to recover and regain their fuel stores. We saw these effects using doses well within the range of what a bird could realistically consume in the wild — equivalent to eating just a few treated seeds.”
The researchers say that the findings suggest that neonicotinoids could have partly contributed to the decline of several bird species in North America that depend on agriculture fields. More than three-quarters of bird species that rely on farmlands have declined in North America since 1966.
“Migration is a critical period for birds and timing matters,” study co-author Christy A. Morrissey, an ecotoxicologist at the University of Saskatchewan, said in the statement. “Any delays can seriously hinder their success in finding mates and nesting, so this may help explain, in part, why migrant and farmland bird species are declining so dramatically worldwide.”
Eng, M. L., Stutchbury, B. J. M., & Morrissey, C. A. (2019). A neonicotinoid insecticide reduces fueling and delays migration in songbirds. Science, 365(6458), 1177-1180. doi:10.1126/science.aaw9419