We captured trumpeter swans (Cygnus buccinator) from the Rocky Mountain population during the winters of 1990-96 at Harriman State Park on the Henrys Fork of the Snake River, Idaho, and during winter 1990 at Red Rock Lakes National Wildlife Refuge, Montana. Captured swans were translocated as part of efforts to restore use of other wintering areas and reduce population vulnerability. In 1990, we tested several capture techniques in severe winter conditions and found night-lighting to be most effective. During 1990-96, we captured 1,117 trumpeter swans by night-lighting, including 1,070 from boats and 47 from snowmobiles and an all-terrain vehicle (ATV). Mean catch/night was 15.1 swans during 71 nights from boats and 4.7 swans during 10 nights from snowmobiles and the ATV. Capture success varied with number of swans present, their prior exposure to night-lighting, and weather conditions, with higher catches in fog ((x) over bar = 19.0) and snowstorms ((x) over bar = 17.1), and lower catches on overcast ((x) over bar = 8.7) and clear nights ((x) over bar = 4.0). A small, lightweight (180-kg) airboat with a reinforced hull and modified to operate in severe winter weather proved indispensable to capture large numbers of trumpeter swans. Most capture attempts occurred during inclement weather when temperatures ranged from 0 degrees to -30 degrees C and required appropriate safety precautions.
