Insectivorous Bird Population Shows Declining Trend in Areas With High Levels of Neonicotinoids

It is not just bees, but also insectivorous birds that are adversely affected by high levels of neonicotinoid pesticides, a new study reveals.

Biologists at the Radboud University Nijmegen and the Sovon Centre for Field Ornithology noticed a dramatic decline in insectivorous birds in farmland areas with high levels of the neonicotinoid insecticide - imidacloprid. The finding is based evaluation of data on local bird population trends and environmental factors that includes concentration of imidacloprid in surface water.

Imidacloprid is the most widely used insecticide in agricultural system. It is also used in horticulture to treat seeds and bulbs and as a crop spray on greenhouse and in the open. This pesticide is known to harm the insects' central nervous system due to which they get paralyzed, disoriented and eventually die. This pesticide has been linked to the drastic decline in bee population and the collapse of bee colonies.

This is the first study that links imidacloprid to the indirect harmful effects on vertebrates. In this study, the researchers combined the data from District Water Boards with systematic bird counts that was 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.

Although what caused the decline is not exactly known, the researchers doubt whether it is a lack of food or consumption of contaminated insects or a combination of the two. For a few species, consuming seeds layered with insecticides cannot be excluded, but the researchers still don't know whether there was a drop in breeding success or mortality was increasing or both.

Hans de Kroon, an ecologist at Radboud University, told the Guardian that 20 nanograms of neonicotinoid per litre of water triggered a 30 percent drop in bird population over ten years.  In few areas, the concentration was 50 times higher.

"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 analyze them rigorously. Thanks to our partnership with organizations such as Sovon, we can discover ecological effects that would otherwise be overlooked," said De Kroon.

The study is published in the journal Nature.