The Same Insecticide That's Killing Bees Is Also Killing Birds

A class of pesticides linked to colony collapse disorder in bee colonies has now been linked to a dramatic decline in insectivorous bird populations. Disturbingly, this could also mean that other animals along the food chain are at risk as well.

Earlier this year, scientists presented some of the most compelling evidence yet that neonicotinoids, a popular form of insecticide, are largely responsible for the destruction of bee populations worldwide.

Now, Dutch scientists from Raboud University have published the first study correlating imidacloprid, a neonicotinoid insecticide, to the marked decline of common insectivorous birds. The chemical, it would appear, is getting to the birds indirectly via the food chain. Imidacloprid, which is the most widely used insecticide in agricultural systems around the world, explains the decline better than other factors, such as land use.

The researchers came to this conclusion after combining 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 were not seen in the counts made before then.

A press release from the researchers explains more:

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.

Bayer, the manufacturer of imidacloprid, rejects the findings, saying it doesn't provide a "causal link" between the chemical and the decline in birds. A spokesperson for Bayer was quoted in the BBC as saying:

Neonicotinoids have gone through an extensive risk assessment which has shown that they are safe to the environment when used responsibly according to the label instructions. Birds living close to aquatic habitats — the species that one could expect to be affected most by concentrations of neonicotinoids in surface water — show no or negligible negative impact.

Ah, so farmers aren't following the instructions. Gotcha.

Scientists say that if insectivorous birds are declining because of the pesticide, than other animals that eat insects may be in trouble as well. To that end, they're looking at populations of bats, hedgehogs, fish, and more to find out.

Read the entire study at Nature: "Declines in insectivorous birds are associated with high neonicotinoid concentrations". Additional information via Raboud University.

Image: Jouke Altenburg.