A letter by a group of scientists on declines in insectivorous birds prepared for Nature magazine and posted online resulted in a response by Bayer CropScience because the company contends there is no demonstrated “causal link between the use of neonicotinoids and the development of bird populations in Europe.”

The letter suggests a possible link between the use of this family of insecticides and a decline in bird populations. As is the case with the Nature magazine and online content, the letter or technical white paper is written in scientific analysis jargon and only available to read by subscribing. Pointing blame at neonicotinoids for more environmental concerns has Bayer trying to counter with its own scientific conclusions.

Bayer’s response follows:

“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.

“The letter makes no proper attempt to account for other possible sources of the reported decline such as climate change or nutrition. On the latter, two of the authors, van Turnhout and Foppen, in 2010 actually concluded that ‘trophic mismatches may have become a major cause for population declines in long-distance migrants in highly seasonal habitats.’ The authors’ conclusion was for forests but agricultural areas are even more seasonal.

“The authors’ assertions ignore the fact that most of the bird species mentioned are not foraging to a large extent on insects emerging from water bodies. Skylarks, for instance, predominantly feed on ground dwelling beetles. Birds living close to aquatic habitats – the species hypothetically affected most by concentrations of neonicotinoids in surface water – show no or negligible negative impact.

“The letter refers to a publication by van Dijk et al (2013) as scientific source which was recently rebutted by peer scientists on methods used and conclusions reached. In addition, the Dutch authority responsible for authorization of crop protection products, Ctgb, concluded ‘that this study cannot be used to show a causal relationship between the concentration on imidacloprid and the number of observed species.’

“In conclusion, the letter to Nature provides no substantiated evidence of the alleged indirect effects of imidacloprid on insectivorous birds. Bayer CropScience is working with the Dutch authorities and agricultural stakeholders to ensure the safe use of imidacloprid-containing crop protection products and to preserve the environment.”