Route Selection to Minimize Helicopter Disturbance of Molting Pacific Black Brant: A Simulation

Abstract

I used a previously described simulation model to assess the effects of helicopter activity on approximately 18 000 molting Pacific black brant (Branta bernicla nigricans) near Teshekpuk Lake, Alaska. Bell 206 and Bell 412 helicopters were simulated flying across the molting grounds along six flight lines at various altitudes and frequencies between two airfields. The model determined the behavioral and energetic responses of every bird encountered by the aircraft during an overflight, then calculated the weight of these birds at the end of wing molt. Body condition of the brant, reflected in weight loss, was used to quantify the impact of helicopter disturbance. The number of birds in each of five risk categories was determined for each route, altitude, helicopter type, and overflight frequency. Flight lines and overflight patterns that minimized disturbance to the molting population were identified. Slightly altering the direct route between the two airfields resulted in up to 91% fewer birds experiencing heavy weight loss. Flying either helicopter type around the southern edge of the molting grounds caused the least disturbance; flying parallel to the coast, 1.6 km inland, caused the most. The Bell 412 caused up to 15% more weight loss than did the smaller helicopter. Weight loss along a given flight line can be reduced by 1) flying at altitudes greater than 1065 m altitude, 2) flying only when most brant are in their second week of molt, 3) minimizing flight frequency, and 4) avoiding use of the larger Bell 412 when possible.

Key words: brant, human disturbance, aircraft, Arctic Coastal Plain, simulation model, feather molt