A pesticide commonly used in Australia has been experimentally shown to cause rapid weight loss in a migrating songbird, and to disrupt its ability to migrate.

Key points: Birds on high doses ate 70 per cent less food and shed lots of weight in the first six hours

Birds on high doses ate 70 per cent less food and shed lots of weight in the first six hours Birds given the pesticide delayed their migration by three to four days

Birds given the pesticide delayed their migration by three to four days But banning neonicotinoids could backfire because farmers might use higher amounts of other types of insecticides that can cause problems

White-crowned sparrows in Canada were given a small, sublethal dose of imidacloprid — a neonicotinoid insecticide — alongside control birds that were given none.

The dose was meant to be equivalent to how much birds would ingest by eating a few very small, insecticide-coated seeds.

Seed coating is a common practice where crop seeds are doused in an insecticide, which is then absorbed into the plant as it grows and is present in the pollen.

In all, 12 birds were given the low dose, 12 were given a higher dose, and 12 were given none.

The birds treated with both the high and low doses shed significant weight within six hours, compared with the control birds that didn't, according to research published today in the journal Science.

"If birds are exposed to a big enough dose, [it's] lethal. A small handful of seeds is enough to kill a songbird," said Christy Morrissey of the University of Saskatchewan, who led the study.

"But what we're seeing is that even an incidental dose can have a substantial effect."

The researchers found the insecticide had an "anorexic" effect, with birds on the higher dose consuming 70 per cent less food than the controls in the six hours following dosing.

The migrating birds were then fitted with lightweight transmitters and released in Ontario, Canada, where their movements were tracked by a network of research towers.

A network of receiver towers allowed the researchers to track the birds' migration. ( Supplied: Margaret Eng )

On average the untreated birds continued their migration within half a day, whereas the birds that had been given the imidacloprid delayed their departure by three days for the low dose and four days for the high.

The hypothesis is that the treated birds spent the extra days working the insecticide out of their system, and then regenerating fat stores to continue their migration.

"The amount we gave them to cause that delay was miniscule," Professor Morrissey said.

"Essentially it was the equivalent of giving a bird one-tenth of a corn seed treated with neonicotinoids."

While there has been some evidence linking neonicotinoids to bee mortality and even colony collapse, Professor Morrissey said her research showed the impacts of pesticides might be much more widespread.

"It's not just a bee problem, or a water problem, this is a pretty compelling case that for birds these [insecticides] are having a pretty serious effect."

Banning neonicotinoids could backfire

Compounding the issue is that many of these birds migrate in spring, which coincides with seeding for many crops, according to Professor Morrissey.

"There are over 200 species in North America that use agriculture as habitat or to feed and rest, and for migratory species it's pretty critical they need to put on fat as a fuel source to go on migratory journeys."

After regaining weight, the birds that were given the insecticide continued on their migration and there was no difference detected in their direction or speed of migration compared to the control birds.

But delaying migration can have ripple effects beyond the immediate impacts to the bird.

As well as exposing them to increased predation as they recover from the insecticide, birds that arrive late to nesting grounds have been shown to secure poorer territory, breed later, and produce fewer offspring.

In North America, 74 per cent of farmland-dependent bird species have been in decline since 1966, the authors state.

Imidacloprid has been linked to the deaths of Australian birds. ( Supplied: Cath De Vaus )

While this research is important, it's not surprising according to agricultural biotechnology expert Caroline Hauxwell of the Queensland University of Technology (QUT), who wasn't involved in the study.

"You feed nasty chemicals to birds and insects, it's not going to do them any good. It's not rocket science," Dr Hauxwell said.

"It shows we have to be very careful about seed coatings and their impacts. Migratory birds are very vulnerable."

Imidacloprid was linked to the deaths of a number of native birds near Horsham in Victoria in 2017.

But Dr Hauxwell warned that we also need to be careful in how we respond, and that simply banning neonicotinoid insecticides could backfire.

Doing so has been shown to force farmers to depend on non-neonicotinoid pesticides instead. These have also been found to impact creatures like bees and birds and often are used in higher volume.

"We could be making a bad situation even more complicated," Dr Hauxwell said.

"It's not just the neonics, it's the fungicides," she said adding that the effect seen on birds exposed to neonicotinoid pesticides has also been found with chlorpyrifos, an organophosphate pesticide.

She said it's also not in the farmers' best interests to have birds eating seeds, but that the solutions need to be more holistic rather than knee-jerk.

Integrated management can help cut pesticides

Coating seeds with pesticides is a common practice in Australia and around the world. ( Supplied: Margaret Eng )

In Australia, seed coating is often used as a default, regardless of whether a specific pest threat is present, according to Dr Hauxwell.

Instead, she said, we could significantly reduce the amount of neonicotinoids used by adopting an integrated pest management approach.

Integrated pest management involves using a range of tactics, including tweaking planting times to avoid pests, creating physical pest barriers, breeding and limiting chemical intervention.

"The golden rule of integrated pest management is that you only respond to the pest threat that you have identified."

Dr Hauxwell said genetic engineering of pest-resistant strains, or transgenics, could also reduce the need for pesticides.

"Most transgenics have been shown to be very benign on non-target species," she said.

Earlier this year the US banned 12 neonicotinoid-based products, and the EU banned three active neonicotinoid substances in 2018, including imidacloprid.

But there have been no signs of a similar ban being implemented here, despite calls from bee keepers to follow in the EU's footsteps.