Songbirds exposed to the world’s most widely used insecticide exhibit “anorexic behaviour” and delay their migration because they needed more time to feed, according to new research. 

This is likely to severely harm their chances of surviving and reproducing, scientists said, adding that imidacloprid could be driving dramatic declines in global songbird populations. 

This research is the first to provide evidence of a link between a group of insecticides called neonicotinoids – applied as spray to 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. 

“Our study shows that this is bigger than the bees – birds can also be harmed by modern neonicotinoid pesticides, which should worry us all,” said Bridget Stutchbury from York University, who was involved in the research, published in the US journal, Science.

A growing body of research is showing that insecticides such as imidacloprid significantly harm a number of species. Scientists believe that birds, which use agricultural environments as habitats or foraging stopovers during migration, are routinely exposed to these pesticides. 

In the experiment, researchers exposed individual sparrows to small doses of the pesticide in southern Ontario during a stopover on their spring migration.

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 3.5 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.

“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 study author Christy Morrissey, an ecotoxicologist from the University of Saskatchewan.

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