A first-of-its-kind study shows a link between insecticide exposure and a decline in migratory songbirds. The new study, published in “Scientific Reports,” examines the possible effects of neonicotinoids on birds like sparrows.
Neonicotinoids are highly controversial because, while insecticide manufacturers claim they are safe, mounting evidence suggests that neonicotinoids harm many bee species and may be driving an overall decline in pollinators.
Given that other animals like birds and rodents feed on crops and seeds treated with neonicotinoids, scientists have wondered if these species experience similar effects.
Of key interest are migratory birds. Because they often begin their long journeys just as crop seeding is underway, these species have a greater likelihood of exposure.
Researchers studied a group of white-crowned sparrows, which as a species migrate from the southern U.S. and Mexico to northern Canada for the summer each year.
The scientists gave a group of captured sparrows a dose of neonicotinoids — either imidaclopridor chlorpyrifos –equivalent to less than that applied to a single corn kernel. The dosage was expected be safe and have no effect on the birds, as per the regulatory framework under which the insecticides are licensed.
However, the researchers found a marked effect. The birds appeared to become weak and stopped eating. Depending on the dose they received, the birds lost between 17 and 25 percent of their total body weight. Crucially, the sparrows also appeared to lose their ability to navigate north, meaning that they would struggle to migrate and expend far more energy trying to reach their destination. Similarly, previous studies have documented that bees may have their own navigational senses impaired by exposure to neonicotinoids.
When the scientists compared these reactions to birds who did not receive a neonicotinoid dose, the difference was marked: They observed no behavioral changes in the control group.
After a few days, most of the birds dosed with neonicotinoids appeared to make a full recovery, further indicating that it was the neonicotinoid dosage that was to blame for the altered mental state and observed behavioral changes.
The researchers note:
The specific under-lying neuronal mechanisms of long-distance migration are largely unknown but it is possible that neurotoxic insecticides that disrupt acetylcholine transmission could have effects on cognitive and motor functions that play important roles in refueling, orientation and navigation.
But this isn’t the first time that researchers explored the impact of neonicotinoid insecticides on birds. Indeed, several studies have shown a potential link. And the evidence has become so convincing that official reports from the European Commission have noted a potential toxic effect on fish, birds and other animals.
Bird decline has been a problem for many years now, with a particularly alarming decline in migratory birds. Studies show that some of North America’s most prominent bird species may have declined in some regions by as much as80 percent since 1967. Other research has suggested that an array of threats may be to blame, including climate change and neonicotinoid-containing pesticides.
However, this study is one of the first to provide a direct causation analysis, meaning that researchers were able to observe the effects of controlled dosing in real-time.
Professor Christy Morrissey of the University of Saskatchewan in Canada, gives insight into how this navigational impairment could be playing a part in species decline, telling the Guardian:
We know from other studies on many different species of migratory birds that if you are delayed by even a few days getting to your breeding ground, or you are in poor condition when you arrive, you have lower reproductive success. We know these effects are really important for population level changes.
What about real-world setting exposure?
While birds are not normally given direct doses of neonicotinoids, these insecticides are often applied to corn — which opportunistic birds and other animals like mice readily feed on. That means that exposure is a viable concern and probably occurring. Of course, researchers will now have to pin down the precise levels of exposure that may trigger changes in behavior – something that Morrissey’s team is now investigating.
Nevertheless, given the significant body of evidence already accumulated, this research tells of a pressing need to reconsider the place of neonicotinoid-containing insecticides in agriculture .
Imidacloprid and chlorpyrifos are highly controversial for their safety to the environment or to humans and a decision on a proposed imidacloprid ban in Canadais being considered, with the federal government expected to make a decision on imidacloprid and its use in Canada sometime in December.
Encouragingly, Environment Secretary Michael Gove recently announced a ban on widespread use of neonicotinoids, bringing the UK in line with Europe’s rolling ban on several neonicotinoids.
This article was first published by Care2.com on 03 Dec 2017.