Identifying agricultural pesticides that may pose a risk for UK birds
The application of pesticides on crops has long been seen as one of the drivers of the decline of farmland bird populations and the latest paper by Cannelle Tassin de Montagu with Dave Goulson from the SBS funded research provides solid evidence of the risks to songbird populations.
What are the threats?
Pesticide use can negatively affect avian population through direct toxicity, altering survival, health and/or reproduction and through indirect pathways such as food reduction and habitat degredation and loss.
Pesticide coated seeds provide a convenient method for pesticide application on crops as they decrease the need to spray, reduce the exposure to the farmer, deposit the active substance on a smaller area and in theory at least decrease the risk to non-target species. However, some seeds are not buried during sowing, remain on the soil and thus are available to granivorous vertibrates.
The study
In this study field experiments determined the exposure of wild birds to pesticides via consumption of fludioxonil- treated winter wheat seeds following autumn drilling. The results were extrapolated for an additional 19 pesticides commonly used as seed treatments, assuming equal consumption rates.
Key findings
11 species were filmed consuming the grain and analysis suggests that that the neonicotinoid insecticides imidacloprid, clothianidin and thiamethoxam represent the highest risk for granivorous birds. For example, chaffinch (Fringilla coelebs) could consume 63% of LD50* of imidacloprid in a single feeding bout, and 370% in a day.
In the study, Chaffinch was found to be most likely to receive a harmful dose of pesticide from seed treated grain, followed by feral pigeon, robin woodpigeon and woodlark. Skylark and sparrows were also seen but not observed eating.
In conclusion:
Large quantities of treated seeds are left available for wildlife to consume after sowing and these are consumed by a broad range of farmland bird species. When extrapolated to other pesticides used as seed treatment this could lead to the ingestion of sufficient pesticide to induce sub lethal and lethal effects. Further work is needed to examine how seed palatability is affected by different seed treatments and how this varies between bird species. If seeds treated with these other pesticides are consumed as readily as those treated with fludioximil, this is likely to cause significant harm.
Importantly there is potential for harm from chemical other than neonicitinoids which until now have received the bulk of attention.
The University team are now working on another field phase of the study to investigate exactly which pesticides turn up in feather samples from wild birds, to understand what harm (if any) they might be doing.
To read more about this study, click below for open access: or download the PDF