Decline of migrating birds could be partly due to pesticides

Authored by newscientist.com and submitted by mvea
image for Decline of migrating birds could be partly due to pesticides

Pesticides can effect white-crowned sparrows Kurt Stricker/Getty

It’s not just bees that are being harmed by the pesticides called neonicotinoids, it’s birds too. A study in Canada has shown that migrating white-crowned sparrows lose weight just hours after eating seeds treated with the neocotinoid imidacloprid, delaying their onward migration by several days. Although the main manufacturer of the pesticide disputes the findings.

Birds that arrive late at breeding grounds are less likely to raise young successfully and sometimes don’t breed at all, says Christy Morrissey at the University of Saskatchewan, Canada, whose team carried out the study. “This has serious impacts on populations.”

In North America, populations of 57 of the 77 bird species associated with farmland are in decline. Morrissey thinks neonicotinoids could be contributing to these declines.

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However, she does not think that banning these pesticides is the answer. Farmers will just use alternative pesticides that may turn out to be just as bad. Instead, we need to find ways of farming that don’t rely on quick chemical fixes, Morrissey says.

Dave Goulson at the University of Sussex agrees. “The regulatory system keeps failing, by allowing new harmful chemicals into use,” he says. “The only long-term solution is to move away from a reliance on pesticides to solve every problem.”

Neonicotinoids are applied to seeds before planting to kill insects that feed on the seedlings. They are much less toxic to birds and mammals than insects, so in theory these animals should not get high enough doses to harm them.

But lab studies by Morrissey have shown that even low doses of imidacloprid make white-crowned sparrows (Zonotrichia leucophrys) lose weight. Now her team has caught wild sparrows on a migratory stopover, tagged them with tiny radio transmitters and fed them either imidacloprid or a harmless control.

Read more: To save the insect world we must go way beyond neonicotinoid ban

Birds given imidacloprid lost up to 6 per cent of their body weight in the six hours before release, whereas those not given the pesticide lost hardly any. Scans also showed a decline in body fat.

After release the birds not fed imidacloprid continued their migration after half a day. Those given imidacloprid did not leave for four days on average. Morrissey says she has unpublished evidence that two other neonicotinoids have similar effects.

The study shows that sublethal doses of neonicotinoids can have adverse effects on seed-eating birds as well as on beneficial insects such as bees, says Caspar Hallmann of Radboud University in the Netherlands. “Birds – especially small birds – are really dependent on having sufficient body fat during migration.”

Hallmann thinks neocotinoids could also be affecting insect-eating birds by depriving them of food. In 2014, he found there were fewer insectivorous birds in areas with high neocotinoid levels in water.

In 2017, Hallmann reported a huge decline in flying insects in Germany, sparking worldwide concern. He thinks pesticides like neonicotinoids are partly to blame.

Morrissey’s findings are disputed by Bayer, the main manufacturer of imidacloprid. Real-world neonicotinoid exposure levels are far below levels that disrupt migratory behaviour, and neonicotinoids are safe when applied according to instructions, says company spokesperson Utz Klages.

Morrissey says the birds were given realistic amounts. A bird could get the highest dose given in the study by eating just a tenth of a treated maize seed, a fifth of a soybean or three canola seeds, for instance. “It’s tiny, tiny amounts,” she says.

Planters are designed to place seeds under the soil, but unburied seeds and seed spills are common, says Morrissey. “Seed spills are a huge and increasing problem,” she says. “Farmers don’t have time to go back and clean them up.”

The European Union has imposed limits on neonicotinoid use, but not a complete ban.

yunus89115 on September 13rd, 2019 at 13:41 UTC »

On a scale of wind turbines to cats, where does this fall as a danger to birds?

SemanticTriangle on September 13rd, 2019 at 12:17 UTC »

When any chemical company says "X is safe, we tested it!" they always just mean its acute toxicity in rats. There is no way to replicate the complexity of natural interactions in the lab, which is why these studies are so important. Yes, field trials take place as well, but these are demonstrably less varied than decades of release.

It's also why these studies get suppressed, ignored, and diluted with junk science by the manufacturers of said chemical, with predictable effects.

The precautionary principle isn't just important because of the limitations of lab work. It's important because commercial entrenchment of a dangerous product is demonstrably difficult to reverse. How many more insecticides have to be shown to be 'Holocene level bad' before we acknowledge that blanket application of any insecticide is harmful? Yes, insecticides are necessary. No, we can't ever use them so carelessly.

mvea on September 13rd, 2019 at 11:29 UTC »

The title of the post is a copy and paste from the first paragraph of the linked academic press release here:

It’s not just bees that are being harmed by the pesticides called neonicotinoids, it’s birds too. A study in Canada has shown that migrating white-crowned sparrows lose weight just hours after eating seeds treated with the neocotinoid imidacloprid, delaying their onward migration by several days

Journal Reference:

A neonicotinoid insecticide reduces fueling and delays migration in songbirds

Margaret L. Eng1, Bridget J. M. Stutchbury2, Christy A. Morrissey3,4,*

Science 13 Sep 2019: Vol. 365, Issue 6458, pp. 1177-1180

Link: https://science.sciencemag.org/content/365/6458/1177

DOI: 10.1126/science.aaw9419

Hazardous delays

Neonicotinoids are a widely used group of pesticides that have been shown to have negative impacts on an increasing number of species, most notably pollinators. Eng et al. tested how exposure to these compounds influenced the behavior of a migrating songbird. Ingestion of field-realistic levels of neonicotinoid insecticides reduced feeding and accumulation of body mass and fat stores, which led to delayed departure from stopover sites. Such delays can lead to reduced migration survival and decreased reproductive success and therefore have the potential to impose population-level impacts.

Science, this issue p. 1177

Abstract

Neonicotinoids are neurotoxic insecticides widely used as seed treatments, but little is known of their effects on migrating birds that forage in agricultural areas. We tracked the migratory movements of imidacloprid-exposed songbirds at a landscape scale using a combination of experimental dosing and automated radio telemetry. Ingestion of field-realistic quantities of imidacloprid (1.2 or 3.9 milligrams per kilogram body mass) by white-crowned sparrows (Zonotrichia leucophrys) during migratory stopover caused a rapid reduction in food consumption, mass, and fat and significantly affected their probability of departure. Birds in the high-dose treatment stayed a median of 3.5 days longer at the site of capture after exposure as compared with controls, likely to regain fuel stores or recover from intoxication. Migration delays can carry over to affect survival and reproduction; thus, these results confirm a link between sublethal pesticide exposure and adverse outcomes for migratory bird populations.