DIETARY SHIFTS AMONG SONGBIRDS FROM A DIFLUBENZURON-TREATED FOREST

Effects of diflubenzuron (a chitin-synthesis inhibiting insecticide) a pplication on diets of forest birds were evaluated in eastern West Vir ginia in 1986. Nine species of songbirds were collected from May throu gh July from treated and untreated plots. Gut contents from each speci men were removed and 10 arthropod taxa were identified. The percentage biomass comprised by each food taxon and total gut biomass was determ ined for each specimen. The diets of five species were significantly d ifferent between treated and untreated plots. In general, biomass of L epidoptera larvae was reduced and biomass of other orders (Homoptera, Diptera, Coleoptera, etc.) was greater at treated sites. In addition, two species displayed reduced total gut biomass at treated sites. Thes e data show that while diflubenzuron is not directly toxic to vertebra tes, birds are affected indirectly through reduced availability of Lep idoptera larvae. Birds possessed differing capabilities to compensate for these diflubenzuron-induced food reductions. Most birds adjusted b y switching prey, while others consumed less food. Resident species ex perienced less impact than did migrants.