AVIAN FORAGING BEHAVIORS AND HABITAT MANIPULATION AT PORTLAND INTERNATIONAL AIRPORT

Between January 1996 and May 2001 more than 300 bird strikes occurred at Portland International Airport. Records indicate that herons and raptors consistently make up nearly one-half of species struck. These species regularly use the airport grassland as a foraging ground, feeding on ground-dwelling rodents, including the graytailed vole (Microtus canicaudus) and vagrant shrew (Sorex vagrans). As part of a current study, various manipulations are being made to the grassland habitat and an assessment will be conducted of their effects on the airfield rodent and avian predator populations. This study will specifically correlate the presence and behaviors of predatory birds with habitat manipulations designed to discourage resident rodent species over a 15- month period. The long-term objectives of the study are to establish standards for frequency of mowing and ideal grass height for Portland International Airport, and to determine whether adherence to these standards may preclude the need for application of poison to reduce numbers of rodents on the airfield