ASSESSING THE HAZARD ITS 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 o f the chemical on a treated seed. In an earlier study, however, it was determined that red-winged blackbirds removed only about 15% of an in secticidal treatment applied to individual rice seeds. Here, we extend those findings by examining the seed-handling behavior of four graniv orous bird species exposed to millet, rice, sunflower and sorghum trea ted with imidacloprid. Mourning doves (Zenaida macroura L,) swallowed the seed whole. House finches (Carpodacus mexicanus Muller), red-winge d blackbirds (Agelaius phaeniceus L.) and boat-tailed grackles (Quisca lus major Vieillot) discarded the seed hulls, however, and removed onl y 15-40% of the initial chemical treatment. Residues on seed hulls dec reased as handling time increased, Sunflowers had the lowest residues because birds repeatedly handled the hull to remove bits of the oily K ernel. These results suggest that avian hazard assessment methods shou ld incorporate species-typical seed-handling behavior to assess more a ccurately birds' exposure to chemicals on different types of seed.