A PROBABILISTIC RISK ASSESSMENT FOR THE KIRTLAND'S WARBLER POTENTIALLY EXPOSED TO CHLORPYRIFOS AND MALATHION DURING THE BREEDING SEASON AND MIGRATION

Two organophosphate pesticides, chlorpyrifos and malathion, are currently undergoing re-registration in the United States and were recently used by the Environmental Protection Agency (USEPA) as case studies to develop a national procedure for evaluating risks to endangered species. One of the endangered bird species considered by the USEPA was the Kirtland's warbler (Setophaga kirtlandii). The Kirtland's warbler is an endangered migratory species that nests exclusively in young jack pine stands in Michigan and Wisconsin, and winters in the Bahamas. We developed probabilistic models to assess the risks of chlorpyrifos and malathion to Kirtland's warblers during the breeding season and spring and fall migrations. The breeding area model simulates acute and chronic exposure and risk to each of 10,000 birds over a 60-day period following initial pesticide application. The model is highly species-specific with regard to the foraging behavior of Kirtland's warblers during the breeding season. We simulated the maximum application rate and number of applications allowed on the labels for representative use patterns that could be found within 3 km of the breeding areas of Kirtland's warbler. The migration model simulates 10,000 birds during the course of their 12- to 23-day migration between their breeding area and the Bahamas. The model takes advantage of over a century of observations of when, where, and for how long Kirtland's warblers forage in different habitats during the course of their migration. The data indicate that warblers only infrequently stopover in habitats that could be treated with chlorpyrifos and malathion. The breeding area and migration models resulted in predictions of very low acute and chronic risk for both pesticides to Kirtland's warblers. These results were expected given that field observations indicate that the Kirtland's warbler has dramatically increased in abundance in recent decades. This article is protected by copyright. All rights reserved