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Starlings and swallows disappear in areas with high levels of neonicotinoids
Jul. 11, 2014
Populations of common insectivorous birds are declining in farmland areas with high levels of the neonicotinoid insecticide imidacloprid. This is shown by an analysis of detailed data on local bird population trends and environmental factors, which include imidacloprid concentrations in surface water. The scientific journal Nature published the study, written by biologists at Radboud University Nijmegen and the Sovon Centre for Field Ornithology, on July 9, 2014
This is the first study that correlates imidacloprid to possible indirect harmful effects – via the food chain – for vertebrates. Imidacloprid is the most widely used insecticide in agricultural systems around the world. It explains the decline better than other factors, such as land use, says Professor Hans de Kroon, who supervised the study. The research was conducted at the Institute for Water and Wetland Research at Radboud University Nijmegen.
The biologists combined the data from the District Water Boards with systematic bird counts taken before and after imidacloprid was introduced in 1995. "The decline in farmland bird species started before 1995, but the local differences in this decline that we have established after the introduction of imidacloprid are not seen in the counts made before that time," says Ruud Foppen of Sovon.
Imidacloprid is used in agriculture and horticulture to treat seeds and bulbs, and as a crop spray in greenhouses and in the open. It affects insects’ central nervous systems, so that they become disorientated and paralysed, and then die. It has also been linked to a decline in bee numbers, and other invertebrates.
The researchers do not yet know precisely what causes the decline. Is it a lack of food? Eating contaminated insects? A combination of both? For a few species, eating seeds coated with insecticide cannot be excluded as an explanation. It is not clear whether breeding success is declining or mortality is increasing, or both.
"Neonicotinoids were always regarded as selective toxins. But our results suggest that they may affect the entire ecosystem. This study shows how important it is to have good sets of field data, and to analyse them rigorously. Thanks to our partnership with organisations such as Sovon, we can discover ecological effects that would otherwise be overlooked ," says De Kroon.
Source: Radboud University
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