Analyzing over 20 years of data, two researchers concluded that pesticide use, not habitat loss, was the most important factor contributing to widespread declines in populations of U.S. grassland birds.
The findings of their statistical study were published in PLOS ONE, the peer-reviewed open-access online scientific publication. Dr. Pierre Mineau, a recently retired senior research scientist on pesticide ecotoxicology with the Science and Technology Branch of Environment Canada, and Mélanie Whiteside of Health Canada, examined the decline of grassland birds across Europe and North America.
The study compared different factors that may be contributing to grassland bird declines on the two continents. This meant looking at the change in cropped pasture, lethal pesticide risk, insecticide and herbicide use, farming intensity and change in permanent pasture. “It was remarkable that loss of permanent pasture did not appear to be much of a predictor of grassland bird declines,” in North America, noted the study authors. And while habitat loss is still a serious concern, the conclusion was that the “use of lethally toxic insecticides cannot be ignored when trying to identify causes of grassland population declines in North America.”
Populations of grassland birds in the United States have declined faster than elsewhere in the world and, while habitat protection has been and remains the main focus of conservationists, the lethal risk to birds from the use of current insecticides appears to be most directly correlated to their declines across the continental states.
The study authors highlighted the difficulty in obtaining statistics on true pesticide use and they stressed the major role that habitat loss plays in bird declines despite their findings, but the pesticide link that emerged in their analysis requires further study.
The pattern of variables contributing to bird declines in Europe, however, was different according to study results. Evidence from Europe suggests that typical habitat dangers including the agricultural intensification and loss of insect food resources were partly responsible for the decline, more so than pesticide applications. This is supported by the fact that European Union regulators use a more precautionary approach to pesticide approvals and place more restrictions and bans on the use of the more dangerous insecticides and herbicides than regulators in the United States.
Among the more alarming conclusions in this study was the finding that “only a small proportion of total cropland need be treated with a dangerous pesticide to affect overall [bird] population trends.” Not only birds that had only “casual association” with treated cropland were affected as a result of immediate and persistent deadly effects, but the lethal impacts were extended through pesticide drift. Pastures that are typically treated with fewer pesticides also proved lethal to many species of birds.