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 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.

“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 journal, Science.

The UK's top birds 2018 Show all 10 1 /10 The UK's top birds 2018 The UK's top birds 2018 10. Chaffinch Down one place on last year. Birdwatch has released this year's rankings for the most frequently spotted birds in the UK. Results were collected from 420,489 British birdspotters Getty The UK's top birds 2018 9. Long-tailed tit Up one place on last year Getty The UK's top birds 2018 8. Robin Redbreast Down one place on last year Getty The UK's top birds 2018 7. Great Tit Up one place on last year Getty The UK's top birds 2018 6. Goldfinch In the same place as last year Pierre Dalous The UK's top birds 2018 5. Woodpigeon In the same place as last year Getty The UK's top birds 2018 4. Blackbird Down one place on last year Getty The UK's top birds 2018 3. Blue tit Up one place on last year Getty The UK's top birds 2018 2. Starling In the same place as last year Getty The UK's top birds 2018 1. House sparrow In the same place as last year Getty

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.

“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, a post-doctoral fellow in the University of Saskatchewan Toxicology Centre and lead author on the study which looked at white-crowned sparrows who 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 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.

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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.