Neonicotinoid harms migratory birds
Researchers show for the first time negative effect of Imidacloprid on wild birdsRead out
Fatal feed: When songbirds eat seeds treated with pesticides, this affects their traction - and, at worst, even their survival, a study reveals. Accordingly, the neonicotinoid imidacloprid inhibits the appetite of the birds and extends their resting time by several days. As a result, the songbirds are more vulnerable to predators, they also arrive late at their destination - and then may no longer find a partner, as researchers report in the journal "Science".
Pesticides are considered to be one of the causes of the dramatic decline in insects, but also of field and songbirds. Above all suspected are the widely used neonicotinoids, which bind to receptors in the nervous system of insects. Nevertheless, these remedies have long been considered harmless to bees - which numerous studies have now refuted. Three of these ingredients, including imidacloprid, are now banned in the EU for outdoor use.A tiny sensor with transmitter enabled researchers to follow bird behavior after re-exposure. © Margaret Eng
How dangerous are neonicotinoids for birds?
For vertebrates, however, the neonicotinoids were considered to be less toxic. But already in June 2019 a mass extinction of singing birds in California aroused massive doubts. Because there were dozens of gold-throats after the treatment of road trees with imidacloprid. Studies on captive-headed birds also indicate that even small doses of this neonicotinoid can massively affect the appetite and orientation of the birds.
But does this also apply to wild migrant birds, for example, when they rest on a sprayed field? Usually Zugv gel use such breaks for eating and thus to increase their fat and energy reserves. "Especially during the spring migration, birds are exposed to particularly high levels of neonicotinoid pollution, because at this time many of the pesticide-treated seeds are being planted, " explain Margaret Eng from the University of Saskatchewan and her colleagues.
Pesticide dose at the rest area
The consequences of eating contaminated seed for migratory birds have now been tested for the first time by Eng and her team on wild roach (Zonotrichia leucophrys). For their study, they caught 36 of these birds during their spring migration in Canada for a short time. Two groups of these birds received 1.2 or 3.9 milligrams of imidacloprid per kilogram of body weight. "These cans are in the range that a bird realistically picks up if it eats only a few treated seeds, " the researchers emphasize. display
All birds were weighed several hours before and after the pesticide administration, then received a tiny sensor and were released back at their "resting place". The researchers then used the sensor to track how the birds behaved and when they resumed their migration.
Shrunken fat reserves and extended break
The result: Even a single dose of imidacloprid had an effect on the train birds. The badgers of both dose groups lost more body weight and fat than the control group in the few hours between pesticide application and release. The researchers attribute this to the fact that the treated birds during these six hours significantly less fraught than their conspecifics.
Even more striking, however: the migratory birds exposed to the neonicotinoid remained much longer at the rest area than the untreated control group. While the latter flew on after half a day break, the rest break in the treated roof chambers took three to four days, depending on the dose. The researchers suggest that this extension of the break is related to the feeding deficit: "It is likely that they delayed their onward flight because they needed more time to regenerate and their energy supplies increase, "says Eng.
Consequences for reproduction and survival
At first glance, such a short delay in migration does not seem to be bad, but for birds this can have serious consequences. First, they are exposed to greater danger from predators on the ground. On the other hand, the longer break leads to the songbirds arriving later in their breeding grounds. "Such a delay can seriously affect their success in mate choice and nest building, " says Eng's colleague Christy Morrissey.
According to the researchers, their findings could at least partially explain why and how neonicotinoids affect the survival of songbirds. "These non-lethal effects of imidacloprid on feeding behavior, physical condition and resting time are clearly related to the survival and reproduction of the birds, " conclude Eng and her team. "They may therefore affect populations of migratory birds that typically use agro-habitats for their regeneration." (Science, 2019; doi: 10.1126 / science.aaw9419)
Source: University of Saskatchewan
- Nadja Podbregar