VARIATIONS IN BREEDING BALD EAGLE RESPONSES TO JETS, LIGHT PLANES ANDHELICOPTERS

We analyzed 3122 observations of military jets, light planes and helic opters for three levels of response (none, alert, flight) by breeding Bald Eagles (Haliaeetus leococephalus) at 13 occupied nests in Arizona and six in Michigan, 1983-85 and 1989-90, respectively. Helicopters e licited the greatest frequency of response (47%), followed by jets (31 %) and light planes (26%). Frequency of response (23-61%) and frequenc y of flight (2-13%) both increased through the nesting season from Feb ruary to June. Distance from eagle to aircraft, duration of overflight and number of aircraft and/or passes were the most important characte ristics influencing eagle responses to pooled and individual aircraft types. Classification tree (CART) models for individual aircraft types provide dichotomous keys of distance and secondary variables affectin g associated response rates, and should facilitate evaluating aircraft -specific impacts. Our analyses indicate a categorical exclusion of ai rcraft within 600 m of nest sites would limit Bald Eagle response freq uency to 19%.