Assessing the Hazard to Granivorous Birds Feeding on Chemically Treated Seeds

Current methods for evaluating hazards to seed-eating birds are based on estimated exposure per unit area and assume that birds ingest all of the chemical on a treated seed. In an earlier study, however, it was determined that red-winged blackbirds removed only about 15% of an insecticidal treatment applied to individual rice seeds. Here, we extend those findings by examining the seed-handling behavior of four granivorous bird species exposed to millet, rice, sunflower and sorghum treated with imidacloprid. Mourning doves (Zenaida macroura L.) swallowed the seed whole. House finches (Carpodacus mexicanus Muller), red-winged blackbirds (Agelaius phoeniceus L.) and boat-tailed grackles (Quiscalus major Vieillot) discarded the seed hulls, however, and removed only 15È40% of the initial chemical treatment. Residues on seed hulls decreased as handling time increased. Sunflowers had the lowest residues because birds repeatedly handled the hull to remove bits of the oily kernel. These results suggest that avian hazard assessment methods should incorporate species-typical seed-handling behavior to assess more accurately birds’ exposure to chemicals on different types of seed