Behavioral response of polar bears to aircraft activity on the northern coast of Alaska

The rapid loss of arctic sea ice is forcing a larger proportion of the Southern Beaufort Sea polar bear (Ursus maritimus) population to spend more time on land, increasing chances of negative interactions between people and bears. In the United States, the Marine Mammal Protection Act (MMPA) protects polar bears from incidental disturbance from human activities. For the remote and roadless areas of northern Alaska, USA, effective management of small aircraft activity is necessary to limit disturbance, but effects of overflights on polar bear behavior are largely unknown. During 2021 and 2022, we intentionally exposed polar bears (n = 115) to systematic aircraft activity (helicopter, fixed-wing) until we observed a disruption of behavior that qualified as a level B take response (e.g., abrupt change in activity or movement) under the MMPA. We used a Bayesian logistic regression to determine what factors influence and can be used to predict when a polar bear will exhibit a level B take response and estimate the probability of an aircraft eliciting a level B take response at different altitudes above the polar bear. Aircraft type, flight altitude, landscape (barrier islands vs. mainland), and bear behavior (active vs. inactive) upon initial aircraft encounter were all important predictors of take. Probability of take rapidly increased with a decrease in flight altitude starting at 450 m for helicopter and 300 m for fixed-wing aircraft. Active (e.g., standing, walking) polar bears on barrier-island landscapes were more likely to experience take than inactive (e.g., bedded) bears on mainland landscapes. Our findings can help with assessments and management plans by quantifying disturbance to polar bears from current and future human activity that involves aircraft use.