Not just the bees but now the birds

A number of articles and papers have been published explaining the harm that insecticides can bring to wildlife, especially bees. However, the battle between scientists and large pesticide companies is still ongoing with disputes over how much damage they really do.

Despite the ever growing number of reports stating the adverse effects these chemicals are having on wildlife they are still widely used in agriculture. In the 1990s a number of neonicotinoid chemicals were introduced as a more environmentally friendly way of dealing with crop pests. While old pesticides were applied through spraying the crops, causing them to effect the wider surrounding environment, neonicotinoids can be applied through coating the crop seed which the plant then absorbs and poisons only the pests that try to eat it. These pesticides are said to target insects’ nervous systems, lowering the threat to mammals and the wider environment. This has led to neonicotinoids to become hugely successful and make up 40% of the global pesticide market.

One of these neonicotinoids is imidacloprid. While manufacturers still state that the evidence of harmful effects is less than substantiated, a new report seems to suggest otherwise. Earlier this week Dutch scientists released a report showing, for the first time, the relationship between the use of imidacloprid and the decline in common birds.

The study, published by Nature, looked at 15 species that depend on insects as their main food source. The researchers examined long term records of the numbers and health of warblers, starlings, thrushes and swallows and compared the dataset to surface water quality. They found that higher concentrations of imidacloprid were ‘consistently associated’ with a decline in many of the assessed birds. During the study the scientists also looked at other possible factors such as land use change or whether the decline had started before the introduction of the insecticide.

It is believed that the chemicals that coat the seeds are leeching out into the surrounding soil and water, and building up over time. This has led to the insecticides killing more insects than intended and therefore having a negative effect on the birds that depend on them. It is thought that the most likely mechanism involved is mortality through food deprivation. Other theories of causation and method were suggested such as the birds are simply eating the chemical coated seeds and that they may be less able to produce or grow their young.

With a 35% decrease in local bird population, it is no surprise investigations into the cause should be taken seriously. However, despite this seemingly strong relationship between imidacloprid and the bird decline, we know that correlation is not the same as causation. The manufacturers of imidacloprid, Bayer, rejected the findings saying that the report doesn’t prove a link between the chemicals and the decline. Neonicotinoids have gone through extensive risk assessments and are said to be safe to the environment when used according to instructions.

The new research strengthens the argument for increased restrictions on pesticide use and more research is being conducted with investigations into the impact on bats, hedgehogs, fish and more. However, it could also be suggested that investigations should be happening on the other side of the battle field.  Instead of pesticide manufacturers simply ‘rejecting’ the evidence against them, maybe they should be conducting their own studies proving that their pesticides are in fact advantageous and worth the potential costs. While many oppose the bans that have resulted from studies such as this one, people are also challenging the manufacturers to provide proof that their neonicotinoids increases yield.

The debate is by no means a simple one with new studies often leading to new questions. Maybe the question should now be; if the pesticides are killing the birds, how are they doing it?

 

For more information on the effect neonicotinoids are effecting birds visit:

http://www.bbc.co.uk/news/science-environment-27980344

http://www.nature.com/news/be-concerned-1.15516

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13531.html

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Abi Gardner

I'm a Ecosystem Services (MSc) student at The University of Edinburgh, with a background in Environmental Geography. I'm passionate about ecology, biogeography, environmental management, sustainability and climate change.

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