Ecological risk assessment framework for low-altitude aircraft overflights: II. Estimating effects on wildlife

An ecological risk assessment framework for aircraft overflights has been d eveloped, with special emphasis on military applications. This article pres ents the analysis of effects and risk characterization phases; the problem formulation and exposure analysis phases are presented in a companion artic le. The framework addresses the effects of sound, visual stressors, and col lision on the abundance and production of wildlife populations. Profiles of effects, including thresholds, are highlighted for two groups of endpoint species: ungulates (hoofed mammals) and pinnipeds (seals, sea lions, walrus es). Several factors complicate the analysis of effects for aircraft overfl ights. Studies of the effects of aircraft overflights previously have not b een associated with a quantitative assessment framework; therefore no consi stent relations between exposure and population-level response have been de veloped. Information on behavioral effects of overflights by military aircr aft (or component stressors) on most wildlife species is sparse. Moreover, models that relate behavioral changes to abundance or reproduction, and tho se that relate behavioral or hearing effects thresholds from one population to another are generally not available. The aggregation of sound frequenci es, durations, and the view of the aircraft into the single exposure metric of slant distance is not always the best predictor of effects, but effects associated with more specific exposure metrics (e.g., narrow sound spectra ) may not be easily determined or added. The weight of evidence and uncerta inty analyses of the risk characterization for overflights are also discuss ed in this article.