1995

Collisions with power lines are a source of mortality to cranes (Grus americana and Grus canadensis), waterfowl, and other birds. We evaluated 2 power line markers for reducing crane and waterfowl mortality in the San Luis Valley, Colorado and examined factors contributing to collisions and marker effectiveness. Collision mortality rates at 8 segments (about 0.8 km each) of power lines marked with either yellow spiral vibration dampers or yellow fiberglass swinging plates were compared with 8 adjoining unmarked segments. During 3 spring and 3 fall migration periods (1988-1991), estimated mortality on study segments was 706, including >35 species. Waterfowl and cranes constituted >80% of mortality. Both marker types reduced mortality (P< 0.005). Birds reacted to marked lines at greater distances and increased their altitude as compared to unmarked lines (P < 0.0001). Factors affecting collisions or marker effectiveness included wind (P = 0.008), nocturnal flights and disturbance (P < 0.005), and age of sandhill cranes (P < 0.001). Neither marker performed better in all study seasons; each may have had unique benefits. Plates damaged distribution lines, precluding their continued use; however, a new marker from Europe which incorporates the benefits of both plates and dampers should be evaluated, as it may best protect against collision losses.