The world's most widely used insecticide has been linked to the dramatic decline in songbirds in North America. A first ever study of birds in the wild found that a migrating songbird that ate the equivalent of one or two seeds treated with a neonicotinoid insecticide suffered immediate weight loss, forcing it to delay its journey.

Although the birds recovered, the delay could severely harm their chances of surviving and reproducing, say the Canadian researchers whose study is published today in Science.

“We show a clear link between neonicotinoid exposure at real-world levels and an impact on birds,” says lead author Margaret Eng, a post-doctoral fellow at the University of Saskatchewan Toxicology Center.

Neonicotinoids, introduced in the late 1980s, were