Birds That Eat Insects in Decline Due to Pesticide

Birds that eat insects are shown to be in decline due to a pesticide, according to a study carried out in the Netherlands. Imidacloprid is a neonicotinoid insecticide and its intended use is for getting rid of insects. It seems that an unintended consequence of using this insecticide is loss of avians as well.

Some birds eat insects, especially during the breeding season, and the insects are also necessary to feed offspring. The absence of insects means breeding and care of offspring are disturbed in some bird species.

The study was carried out by researchers in the Institute of Water and Wetland Research, Departments of Experimental Plant Ecology and Animal Ecology and Eophysiology at Radboud University in the Netherlands. The results of the study showed that imidacloprid concentrations more than 20 nanograms per liter were associated with bird populations declining by 3.5 percent annually. Also, this decline in the bird population only appeared in the Netherlands after the introduction of imidacloprid in the 1990s. A decline in 14 species of birds was identified in the study.

It has been known for a long time that this pesticide has played a role in the decline of some species of bees. Maintaining proper amounts of bees in the environment is important for agriculture. Bees are necessary for pollination without which crops will not yield their fruits and vegetables.

Some have suggested that this finding is reminiscent of Rachel Carson’s Silent Spring scenario. However, the report is too limited and specific to an area to indicate that the problem is that severe. Continued assessment of the effects of neonicotinoid insecticides is, however, certainly warranted. A two-year moratorium on the use of some neonicotnoids on flowering crops has already been declared in Europe.

The method for administering neonicotinoid insecticides on crops is no longer simply spraying a field. Instead, seeds come preloaded with neonicotinoid coatings and the insecticide subsequently becomes incorporated into every part of the plant. Every branch and bud, root, stem or flower has the insecticide in it and so if pests eat any part of the plant, they will become sick or die. The pollen and nectar produced contain the chemicals as well. Insecticides are neurotoxins and are therefore poisons. The chemicals can travel away from the intended farm area through water run-off and other means and so other plants on the other side of a fence can be affected as well.

There are a few ways that pesticides can cause a decline in the population of  insect-eating birds. They can die from use of the pesticides themselves. If a bird eats a coated seed, for example, it can either have difficulty flying or become immobile. The effect, however, does not come only from loss of their food source.

This study was the first to report evidence for extended effects of this insecticide in an ecosystem. It is an example of how use of an insecticide intended for one purpose can affect biodiversity.

Critics of the study have said that a correlation may have been substantiated by the ressearch, however, a causal link is necessary to confirm the conclusion. Further studies will undoubtedly be carried out to elucidate how and why pesticide is causing declining populations of birds that eat insects.

By Margaret Lutze

Nature (Declines in insectivorous)
Nature (Be Concerned)
National Geographic


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