The world's most widely used insecticide has been linked to a global decline in songbirds.

Researchers say neonicotinoids, which have also been shown to harm bees, can cause migrating birds to suffer dramatic weight loss and lose their sense of direction.

The team say eating just three or four seeds a day treated with the chemicals caused problems.

Some of the birds used in the study at a research site at the Facility for Applied Avian Research at the University of Saskatchewan, in Emlen funnels, a bird cage shaped like an inverted cone used to study their behaviour and migratory instincts.

NEO-NICOTINOIDS The pesticides - known as neo-nicotinoids or 'neo-nics' - are meant to kill insects that eat crops. They are used in sprays and coatings on seeds – killing sap-sucking weevils and aphids. Increasing evidence shows they also cause harm bees' ability to forage for food and to reproduce. Scientists who tested 198 honey samples from every continent except Antarctica discovered that 75 per cent were laced with at least one of the neonicotinoid chemicals. The European Commission proposed a ban on three neonicotinoids on flowering crops such as oil seed rape in 2013 because of the threat to bee health. The UK had originally opposed the ban. Advertisement

'These chemicals are having a strong impact on songbirds.

'We are seeing significant weight loss and the birds' migratory orientation being significantly altered,' said Margaret Eng at the University of Saskatchewan in Canada, a post-doctoral fellow, who also worked with colleagues from York University on the research.

'Effects were seen from eating the equivalent of just three to four imidacloprid treated canola seeds or eight chlorpyrifos granules a day for three days.'

The research is the first study to show that imidacloprid (neonicotinoid) and chlorpyrifos (organophosphate) - two of the most widely used insecticides worldwide -are directly toxic to seed-eating songbirds.

The paper, published in Scientific Reports, shows these chemicals can directly affect songbird migration.

'Studies on the risks of neonicotinoids have often focused on bees that have been experiencing population declines,' said Christy Morrissey, the biology professor who runs the lab the study was carried out in.

'However, it is not just bees that are being affected by these insecticides,'

Neonicotinoids have become the most popular class of insecticides among farmers because they are very successful at killing pests and are easy to apply.

'In the past farmers might have placed an insecticide into a crop duster and would spray their fields with the insecticide.

During a spring migration, Morrissey and Eng captured sparrows, which were then fed daily for three days with either a low or high dose of imidacloprid or chlorpyrifos

'However, now farmers have access to seeds that in many cases are already coated with neonicotinoids,' said Morrissey.

'Birds that stop on migration are potentially eating these seeds, but can also mistakenly ingest the chlorpyrifos pellets for grit, something they normally eat to aid in the digestion of seeds.'

During a spring migration, Morrissey and Eng captured sparrows, which were then fed daily for three days with either a low or high dose of imidacloprid or chlorpyrifos.

Lab experiments showed that the neonicotinoids changed not only the birds' migratory orientation, but the birds also lost up to 25 per cent of their fat stores and body mass, both of which are detrimental to how a bird successfully migrates.

'What surprised us was how sensitive and rapid the effects were, particularly to imidacloprid,' said Morrissey.

'The birds showed a significant loss of body mass and signs of acute poisoning (lethargy and loss of appetite).

Lab experiments showed that the neonicotinoids changed not only the birds' migratory orientation, but the birds also lost up to 25 per cent of their fat stores and body mass, both of which are detrimental to how a bird successfully migrates. Pictured, a House Sparrow (Passer domesticus) perched on a branch in Victoria, Vancouver Island, British Columbia, Canada.

'The migration trials also showed that birds completely failed to orient or changed their northward orientation.'

'Many small migratory songbirds use agricultural land as a stopover to refuel on long flights.

'These neurotoxic insecticides are widely used in North America but their effects on migratory ability in birds have not been tested before ' said York U biology researcher Bridget Stutchbury.

'Although neonicotinoids were thought to have a lower toxicity to vertebrates, it actually proved to be more harmful to these songbirds than the older organophosphate chemicals.'

Morrissey said that this research 'could have major implications for regulation decisions of these pesticides.'

Imidacloprid and chlorpyrifos are highly controversial for their safety to the environment or to humans and a decision on a proposed imidacloprid ban in Canada is being considered, with the federal government expected to make a decision on imidacloprid and its use in Canada sometime in December.'

'We were encouraged that most birds survived, and could recover following the cessation of dosing,' said Eng.

'But the effects we saw were severe enough that the birds would likely experience migratory delays or changes in their flight routes that could reduce their chance of survival, or cause a missed breeding opportunity.'

A spokesman for Bayer, which makes imidacloprid, told The Guardian: 'Scientific evidence shows that imidacloprid has minimal environmental impact when used according to the label, including ingestion by seed-eating songbirds. We take the safety and environmental impact of our products seriously.'