"Neonicotinoids," a class of neuro-active insecticides chemically similar to the nicotine found in cigarettes, is being blamed as the cause of a massive die-off of bees and some species of birds in Canada and the U.S.

Neonicotinoids were originally intended to defend and protect food crops from disease or infection. A recent Dutch study of Canadian farmlands has found this isn't the case.

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It's discovered the strongest evidence yet that neonicotinoids are harming insect-eating birds like swallows. A second part of the study shows that neonicotinoids impair the foraging skills of bumblebees, causing a previously unexplained mass die-off of bees.

The study noted that neonicotinoids are neurotoxins especially lethal to insects that birds eat. After being sprayed onto crops, the neonicotinoids coat seeds and are absorbed by plants as they grow.

After some time, small amounts of the neurotoxin spread throughout plant tissues, including a flower's nectar and pollen.

The Dutch cited "imidacloprid," the first commercial neonicotinoid and one of the most common. Imidacloprid was developed by German chemical and pharmaceutical company, Bayer AG.

The study noted that on farms where imidacloprid concentrations in surface water were highest (over 20 nanograms per liter), bird populations dropped by 3.5 per cent annually on average.

The problem doesn't appear to be that the pesticide is toxic to birds. Rather, the pesticide is depleting the birds' food supply by killing off too many insects. In other words, the pesticide is doing its job far too well.

"The problem is, it is too good. You don't need to kill every insect in the field 24/7," said Pierre Mineau, a toxicologist now working as a consultant for groups such as the American Bird Conservancy.

The study published in the journal Nature concludes that neonicotinoids appear to pose an "even greater risk than has been anticipated" and warns of "potential cascading effects" on ecosystems.

Other studies also show that concentration of neonicotinoids associated with bird declines in Dutch farms often exceeded those in farms in the U.S. and Canada where many insect-eating birds are being killed-off.