A much anticipated update on wind turbines and birds in California’s Altamont Pass concludes that the problem is more severe than once believed. The report by biologists Carl Thelander and Sean Smallwood for the National Renewable Energy Laboratory estimates that somewhat more than 1,000 birds are being killed annually by about 5,000 wind turbines in the pass. One-half of the birds killed are raptors. This is significantly more than that estimated by studies in the 1990s.
However, the study also estimated that only 24 golden eagles (Aquila chrysaetos) are killed annually, about one-half of that estimated earlier. The golden eagle is a protected species. Most of the raptors killed are red-tailed hawks (Buteo jamaicensis).
The study also concluded that the mortality rate per turbine is nearly ten times that of the previous estimates. Earlier studies suggested the mortality rate ranged from 0.02 to 0.05 birds killed per turbine per year. The new NREL study puts the death rate at 0.19 birds/turbine/year.
In the carefully chosen words of science, the authors suggest that the California wind industry has an ongoing problem in the Altamont Pass. The implications of the data in this study and that of companion studies by the California Energy Commission led to a highly-public dispute between the Center for Biological Diversity and Alameda County over permits to repower the Altamont Pass.
The California industry has argued that repowering will cut the number of birds killed. The NREL report explicitly calls this into question. “The number of bird fatalities per turbine string increases in relation to the total rotor swept area . . . it is reasonable to infer that reducing the number of turbines in a particular area will not result in a reduction in bird fatalities unless the total rotor swept area is also reduced.” This conclusion contradicts that of an earlier study.
In a similar contradiction of earlier work, the new study found more birds were killed by wind turbines on tubular towers in the Altamont Pass than those on lattice towers. This finding calls into question claims made in Alameda County’s environmental impact report on repowering that new turbines on tubular towers will significantly reduce bird kills.
Equally as sobering, the authors suggest that the impact of the turbines on burrowing owls (Athene cunicularia) may be more severe than that on golden eagles. “This species is becoming increasingly rare throughout California. . . To address this unique circumstance, more research is needed on the effects of turbine kills on this local population . . . and possible emergency management options that will reduce those impacts.”
Most damaging to claims in Alameda County’s environmental report is the study’s conclusion that “it is reasonable to expect that the number of bird fatalities at fewer post-repowering turbine should remain nearly equal to the number of kills reported at the more numerous pre-repowering turbines.”
If Thelander and Smallwood’s projections are borne out in practice, wind turbines in the Altamont Pass–post-repowering–will continue to kill about 1,000 birds per year, including a potentially significant number of golden eagles and burrowing owls.
“Bird Risk Behaviors and Fatalities at the Altamont Pass Wind Resource Area” by C.G. Thelander, K.S. Smallwood, and L. Rugge of BioResource Consultants in Ojai, California, NREL/SR-500-33829, December, 2003, www.nrel.gov/docs/fy04osti/33829.pdf.
