Dietary Shifts among Songbirds from a Diflubenzuron-Treated Forest

Abstract

Effects of diflubenzuron (a chitin-synthesis inhibiting insecticide) application on diets of forest birds were evaluated in eastern West Virginia in 1986. Nine species of songbirds were collected from May through July from treated and untreated plots. Gut contents from each specimen were removed and 10 arthropod taxa were identified. The percentage biomass comprised by each food taxon and total gut biomass was determined for each specimen. The diets of five species were significantly different between treated and untreated plots. In general, biomass of Lepidoptera 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. These data show that while diflubenzuron is not directly toxic to vertebrates, birds are affected indirectly through reduced availability of Lepidoptera larvae. Birds possessed differing capabilities to compensate for these diflubenzuron-induced food reductions. Most birds adjusted by switching prey, while others consumed less food. Resident species experienced less impact than did migrants.