Conventionally managed orchards receive extensive applications of anticholinesterase (anti-ChE) insecticides throughout the growing season. Because many avian species make use of these environments for nesting and foraging, they may receive substantial exposure to anti-ChEs. The model used to assess avian risk in these environments is highly simplified, and indicator species used in risk studies may misrepresent the risk of the species in the field. A better understanding of avian risk is needed, and should begin with a closer examination o# their exposure in these environments. Exposure of free-flying birds was examined in two conventional orchards during the nesting seasons of 1999 and 2000. Our goal was to demonstrate the influences of species and chemical differences on the exposure we observed. Plasma ChE activity and ChE reactivation were used to identify exposure in multiple species following anti-ChE applications (applied singly and in mixtures). Chipping sparrows (Spizella passerina), American goldfinches (Carduelis tristis), and American robins (Turdus migratorius) demonstrated significant ChE activity depression in 1999 (p 0.005), and only chipping sparrows demonstrated significant depression in 2000 (p = 0.0002). These three species demonstrated the highest proportion of exposed individuals among all species examined in both years. Because many chemicals were simultaneously present in each orchard, chemical influences on the exposure we observed could not be discerned. This work does demonstrate, however, that avian species differ significantly in their exposure, and that chipping sparrows demonstrated the greatest exposure among the species analyzed. These results underscore the need for multiple species studies and for choosing indicator species on a biologically relevant basis.
