About half of the birds killed are raptors, Thelander believes, including about 50 golden eagles a year. These are not classified as threatened or endangered under the Endangered Species Act, but they are specifically protected in the US by the Bald Eagle Protection Act. Although golden eagles are the birds of greatest concern, Thelander's study team found only five dead ones, compared to 74 hawks and 43 owls. One type of owl killed, the burrowing owl, may soon be classified as a threatened or endangered species, Thelander warns.
But based on much higher numbers of dead golden eagles found outside his study area, Thelander estimates a higher proportion of eagles killed Altamont-wide. Windsmiths reported 50 other golden eagles killed between January 1998 and March 2000.
"The Altamont issue has not been resolved, it remains an enigma," Thelander said. "But clearly the Altamont is a unique situation. Industry-wide, bird kills and raptor kills won't be a barrier to wind development."
One factor contributing to the high rate of raptor deaths at the Altamont Pass may be soil disturbance from road construction for the wind farms and tower platforms. Thelander believes that the soil disturbance attracts burrowing animals like ground squirrels, which are a favoured prey for the raptors.
He is not certain that repowering wind farms in the area will reduce the number of bird kills, but he is optimistic that could be the case. Only time will tell. "Logic would tell you would have fewer kills from fewer turbines, but they will have larger swept areas so you might not," he comments. But he wonders if a mere reduction will be sufficient. "We're not going to get zero fatalities, but legally you're not allowed to kill a golden eagle. We're killing 50 golden eagles a year now. If you reduce that to ten or 20 -- the electric industry has been prosecuted for killing less." In a repowering planned by FPL Energy, old Kenetech 56-100 machines will be replaced by new NEG Micon turbines at a rate of seven-to-one.
Many in the wind industry have assumed that by moving away from lattice towers with horizontal bars and smaller rotors with high rotational speeds, bird kills will be reduced. "Our data shows those assumptions are not true," Thelander asserts. Most of the turbines in his study area were not horizontal lattice towers, and although large rotors have fewer revolutions per minute, the rotor tip speed is about the same, posing the same risk to birds.
Forward progress is imperative to avoid being prosecuted by federal wildlife agencies. "The Fish and Wildlife Service has a policy that if utilities and generating companies are responsible and are improving their systems, then they generally don't prosecute," says Thelander. "And utilities are making progress," he notes. "The wind industry will be looked at under the same guidelines."