Using the terrestrial residue exposure (T-REX) model to assess threatened and endangered bird exposure to and risk from pesticides.

The Terrestrial Residue Exposure (T-REX) model, a spreadsheet-based model developed by the US Environmental Protection Agency (USEPA), is used to estimate the concentrations of pesticides on some representative avian terrestrial food items after a foliar pesticide application. T-REX uses 6 categories of food items to assess exposure for birds. Different body size classes are used to estimate diet intake levels and to demonstrate different exposures for different size birds with various single component diets. The purpose of this analysis is to determine whether T-REX is a sufficient tool to assess exposure to the majority of threatened and endangered (T&E) bird species in the United States based on diets and body sizes of listed species. Our analysis combining diets and body weights of T&E species finds that no listed species weighing less than 50 g consumes primarily plant matter. Therefore, the hypothetical bird included in T-REX weighing 20 g and consuming only short grass that is predicted to have the highest exposure does not represent any T&E bird species. Many T&E species are represented when T-REX considers risk for insectivorous species in the 20-g size class. However, no T&E species that are predominantly insectivorous occur in the larger 100 and 1000-g size classes. Fruit and seed-eating T&E species occur in each of the size classes that T-REX considers, so fruit and seed-eating T&E birds are adequately represented in T-REX. T-REX does not include any estimated environmental concentrations (EECs) for aquatic dietary items or nectar, terrestrial vertebrates, soil-dwelling organisms, and noninsect invertebrates (e.g., snails). More than a third of T&E species have diets that are not represented in any of the dietary categories included in T-REX. Slightly more than half the species have diets that include large contributions by dietary items not included in T-REX. An analysis of risk using only T-REX based on simplistic diets is not adequate for a comprehensive assessment of risk from pesticides for all T&E bird species.