| Farmland bird species are known to be declining. In Europe, studies conducted at the farm-level have attributed this decline in abundance, at least partly, to agricultural practices including pesticide use. In North America, few studies have attempted to investigate the relationship between pesticide use and bird abundance and richness. Lack of sufficiently comprehensive pesticide data often limits rigorous testing of hypotheses. I therefore used the best available records of pesticide use and bird distributions: those in California. I calculated estimates of area treated with pesticides and insecticide direct toxicity. I related these to the spatial and temporal variation in bird species richness and abundance (from the Breeding Bird Survey) over a ten-year period in 5.0 km2 plots distributed over the Central Valley of California. I found that the relationships between bird species richness and abundance and pesticide use are weak, albeit borderline significant. I suggest that, if pesticide use actually does affect breeding bird abundance, it must be at much broader spatial scales than used in this study. |
