Farmers’ leaders have questioned research published this week which suggests an insecticide is a key factor in a recent decline in farmland birds.

Scientists have written a report, published in science journal Nature, which looked at the effects of the most widely used neonicotinoid insecticide, imidacloprid, on bird populations in the Netherlands,

The study, led by Hands de Kroon of Radboud University in the Netherlands, found greater declines of bird populations in areas with higher surface water concentrations of imidacloprid.

A two-year European Union suspension on certain neonicotinoids began at the end of 2013 over fears over their effects on bees and other pollinating insects.

National Farmers’ Union (NFU) vice president Guy Smith, who farms at St Osyth, near Clacton, described the link found between the surface water concentrations of imidacloprid and declines in certain bird species in the Netherlands as “interesting”, but argued that it did not demonstrate that pesticide use causes bird decline.

“Changes in habit, climate and cropping patterns could all contribute to shifts in bird population,” he said.

“The study itself acknowledges that: “Food resource depletion may not be the only or even the most important cause of decline,” but it fails to investigate or even mention any other factors.

“The researchers assert that consumption of contaminated insects could have a direct impact on birds, but they provide absolutely no evidence to support this highly suggestive statement, which has caused a lot of sensationalism in the media today around ‘pesticides killing birds’.

“In the UK, the use of pesticides is tightly regulated and monitored. The study states that the use of imidacloprid in the Netherlands regularly results in the permitted environmental concentrations being exceeded – if such problems are detected in the UK, measures are rapidly implemented to avoid potential negative impacts on the environment.

“The NFU fully supports Prof. Charles Godfray’s response to the article where he states that there’s an enormous importance in setting up large, replicated field experiments in real agricultural landscapes to get much harder data on the effects of this class of insecticide on all elements of biodiversity.”

The researchers who wrote the study said: “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.”