Avian consumption of blank pesticide granules applied at planting to Iowa cornfields

Abstract

AbstractConsumption of pesticide granules by free‐ranging birds was quantified by applying blank (untreated silica granules to Iowa cornfields at rates varying from 3.9 to 17.3 kg/ha and examining the gizzards of birds collected from these fields for the presence of granules. One or more granules were found in the gizzards of 39% of 256 birds collected. Counts of gizzard granules averaged 0.6 to 0.9 for the three avian groups collected (horned larks, blackbirds, and sparrows). More than 95% of the specimens contained ≤3 granules; the maximum count was 6. On the basis of granule voiding experiments, we estimate that gizzard examinations detected 24% of the granules consumed per day. Median daily consumption for birds in general was estimated to be 2.4 granules, with 95% of individuals estimated to consume ≤18 granules. For the species with the highest consumption rate, the savannah sparrow (Passerculus sandwichensis), median consumption was 11 granules per day, with 95% of individuals estimated to consume ≤23 granules per day. Granule availability on the soil surface was highly correlated with the application rate. Counts within the application band immediately after application averaged 15 granules/ft2 for every 1 kg/ha applied, or about 6% of the granules applied. Our results suggest that when granular pesticides are applied to cropland, many birds may ingest granules, but the numbers ingested will generally be low.