Common agricultural birds are in decline, both in Europe and in North America. Evidence from Europe suggests that agricultural intensification and, for some species, the indirect effects of pesticides mediated through a loss of insect food resource is in part responsible. On a state-by-state basis for the conterminous Unites States (U.S.), we looked at several agronomic variables to predict the number of grassland species increasing or declining according to breeding bird surveys conducted between 1980 and 2003. Best predictors of species declines were the lethal risk from insecticide use modeled from pesticide impact studies, followed by the loss of cropped pasture. Loss of permanent pasture or simple measures of agricultural intensification such as the proportion of land under crop or the proportion of farmland treated with herbicides did not explain bird declines as well. Because the proportion of farmland treated with insecticides, and more particularly the lethal risk to birds from the use of current insecticides feature so prominently in the best models, this suggests that, in the U.S. at least, pesticide toxicity to birds should be considered as an important factor in grassland bird declines.

We used pesticide use data and previously published models to estimate the lethal risk to birds from insecticides used in U.S. agriculture. Data from the U.S. Department of Agriculture's National Agricultural Statistical Service (NASS, Washington, D.C.) were used to assess how the lethal risk to birds has changed over the period 1991 to 2003 and to compare risk among crop types according to the most recently available surveys. Because the NASS data coverage is incomplete, both with respect to crop and state, we also used a database assembled by the National Center for Food and Agriculture Policy (NCFAP, Washington, D.C.) for the 1997 reference year, to which we added state-specific average application rates for crop/insecticide combinations. For each state/crop/insecticide combination (>6000 entries), we assessed the proportion of crop area on which avian mortality was deemed probable, as well as the extended number of hectares this represented. The crops responsible for most potential bird mortality in the United States were corn and cotton, followed more distantly by alfalfa, wheat, potato, peanut, sugar beet, sorghum, tobacco, and citrus. Other crops represented a higher risk to birds on a per hectare basis. The southeast United States generally had the highest proportion of farmland with a lethal risk to birds. On a positive note, the lethal risk to birds has generally declined over the last decade in most crops, although there are exceptions such as small fruit crops. The reasons for this improvement vary from crop to crop, but usually entail the replacement of older more hazardous products with newer ones with lower acute toxicity to birds.

No abstract