Capturing trumpeter swans by night-lighting

We captured trumpeter swans (Cygnus buccinator) from the Rocky Mountain pop ulation 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 Na tional Wildlife Refuge, Montana. Captured swans were translocated as part o f efforts to restore use of other wintering areas and reduce population vul nerability. In 1990, we tested several capture techniques in severe winter conditions and found night-lighting to be most effective. During 1990-96, w e captured 1,117 trumpeter swans by night-lighting, including 1,070 from bo ats and 47 from snowmobiles and an all-terrain vehicle (ATV). Mean catch/ni ght was 15.1 swans during 71 nights from boats and 4.7 swans during 10 nigh ts from snowmobiles and the ATV. Capture success varied with number of swan s present, their prior exposure to night-lighting, and weather conditions, with higher catches in fog ((x) over bar = 19.0) and snowstorms ((x) over b ar = 17.1), and lower catches on overcast ((x) over bar = 8.7) and clear ni ghts ((x) over bar = 4.0). A small, lightweight (180-kg) airboat with a rei nforced hull and modified to operate in severe winter weather proved indisp ensable to capture large numbers of trumpeter swans. Most capture attempts occurred during inclement weather when temperatures ranged from 0 degrees t o -30 degrees C and required appropriate safety precautions.