Most widely used insecticide 'makes songbirds anorexic'
Passerines exposed to the world’s most widely used insecticide exhibit "anorexic behaviour" and delay their migration because they need more time to feed, according to new research.
On top of this delay, the birds' chances of surviving and reproducing are severely lowered, with the reality that imidacloprid – a commonly used insecticide – could be driving dramatic declines in global songbird populations. This research is the first to provide evidence of a link between these neonicotinoids, which are applied as spray on most major crops worldwide, and the overall population declines observed in many migratory species.
Previously, the toxic effects of neonicotinoids were only thought to affect insects. However, Bridget Stutchbury of from York University, who was involved in the research, said: "Our study shows that this is bigger than the bees – birds can also be harmed by modern neonicotinoid pesticides, which should worry us all."
A growing body of research is showing that insecticides, such as imidacloprid, significantly harm several species. Scientists believe that birds, which use agricultural environments as habitats or foraging stopovers during migration, are routinely exposed to these pesticides.
"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," said Margaret Eng, from the University of Saskatchewan Toxicology Centre and lead author on the study, which looked at White-crowned Sparrows that consumed small doses of imidacloprid.
In the experiment, researchers exposed individual sparrows to small doses of the pesticide in southern Ontario during a stopover on their spring migration. Each bird’s body was measured before and after exposure. A lightweight radio transmitter was attached to the bird’s back.
They found birds given a higher dose of the pesticide lost 6 per cent of their body mass within just six hours. One dose caused birds to stay three-and-a-half days longer at the stopover site before resuming their migration, scientists found.
"Both of these results seem to be associated with the appetite suppression effect of imidacloprid. 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," said Dr Eng.
In North America, three-quarters of bird species rely on agricultural land that has significantly declined since 1966. This study shows pesticides could be directly contributing to catastrophic declines in birds.
"Migration is a critical period for birds, and timing matters. 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," said Christy Morrissey, an ecotoxicologist from the University of Saskatchewan.