Differences in flight behavior between White-tailed and Steller's Sea Eagles in Hokkaido

Abstract

In Japan, 16 White-tailed Eagles Haliaeetus albicilla have been confirmed killed in collisions with wind turbines. For Steller's Sea Eagles H. pelagicus, however, only one bird is known to have collided with a wind turbine. In order to determine why Steller's Sea Eagles collide with wind turbines much less frequently than White-tailed Eagles, we studied the flight behavior of the two species between 2007 and 2009 in Hokkaido, northern Japan.
The altitude of flight was significantly higher for Steller's Sea Eagles than for White-tailed Eagles, which frequently flew at altitudes within the height range for the rotor-swept area of wind turbines (50-100 m). The frequency of flight activity was also much higher for White-tailed Eagles than for Steller's Sea Eagles. These results confirm that White-tailed Eagles are at higher collision risk than Steller's Sea Eagles.
The flight altitude of migrating eagles was significantly higher than that of wintering and resident birds. It is suggested that measures should be taken to reduce collision risk primarily for wintering and resident eagles. Since migrating eagles generally fly at lower elevation when landing after their cross-ocean trip, however, they may enter the collision risk zone. Therefore, in areas where wind farms are located along points-of-arrival for migrating eagles, measures should be taken to reduce the collision risk for migrating eagles as well.