Recent studies have shown that neonicotinoid insecticides have adverse effects on non-target invertebrate species1,2,3,4,5,6. Invertebrates constitute a substantial part of the diet of many bird species during the breeding season and are indispensable for raising offspring7. We investigated the hypothesis that the most widely used neonicotinoid insecticide, imidacloprid, has a negative impact on insectivorous bird populations. Here we show that, in the Netherlands, local population trends were significantly more negative in areas with higher surface-water concentrations of imidacloprid. At imidacloprid concentrations of more than 20 nanograms per litre, bird populations tended to decline by 3.5 per cent on average annually. Additional analyses revealed that this spatial pattern of decline appeared only after the introduction of imidacloprid to the Netherlands, in the mid-1990s. We further show that the recent negative relationship remains after correcting for spatial differences in land-use changes that are known to affect bird populations in farmland. Our results suggest that the impact of neonicotinoids on the natural environment is even more substantial than has recently been reported and is reminiscent of the effects of persistent insecticides in the past. Future legislation should take into account the potential cascading effects of neonicotinoids on ecosystems.
We thank A. J. van Dijk, H. Sierdsema and D. Zoetebier for processing the bird data sets and J. P. van der Sluijs for sharing the database with imidacloprid concentration measurements. The Breeding Bird Monitoring Program is organised in close collaboration with Statistics Netherlands and provinces and is funded by the Dutch Ministry of EZ. We thank Sovon volunteers for their efforts in the field. The study was supported by NWO grants 840.11.001 and 841.11.007 and was the result of a collaboration within the Center for Avian Population Studies.
Extended data figures
This file contains Supplementary Data, Supplementary Methods and Supplementary References.