The deadly windmills of Altamont

Bird deaths at wind farms deplete regional populations

For the 35,330 - 94,426 birds killed over the past 20 years by wind machines, Altamont Pass holds the deadliest wind farm in North America.

The Altamont Pass Wind Resource Area is situated in prime raptor habitat along one of North America's main bird-migration routes. The grasslands there are rich in food for raptors, including ground squirrels, gophers, voles, rabbits, hares, reptiles, amphibians, and arthropods. Historically it has supported one of the highest known densities of breeding pairs of golden eagles in the world.

Raptors killed at Altamont include eagles (75-116 per year), kites, falcons, hawks, harriers, and owls. Other victims include waterfowl, ravens, swallows, shrikes, woodpeckers, larks, and numerous other songbird and bat species. Many of these species are in decline throughout California. Golden eagles and burrowing owls are of greatest concern because of their low reproductive rates and the accelerating destruction of their habitat throughout their range in California.

Birds try to pass through rotating turbine blades probably because they cannot see them. It is likely that raptors spot a prey item or perching spot and fixate on it until they capture it or land there. If there are rotating blades in the way, the raptor may not see them, or may see them too late. Species with varying behavioral instincts differ in susceptibility. Wind farms contain towers, wires, fence posts, and other structures which birds may perceive as perching and nesting sites and are thus attracted precariously close to turbines.

Turbine factors affecting avian mortality include tip speed, tower type, time in operation, topography, height, placement, and spacing.

Recent research reveals that bird mortality has been grossly underestimated; industry monitoring reported only 13% of actual bird deaths. Each bird fatality is a violation of federal and state law, yet Alameda County recently renewed the permits for most of the wind machines (see accompanying article). To date, none of the responsible agencies have taken any meaningful action to decades of ongoing raptor mortality.

Several strategies to reduce mortality have proven ineffective. Worst perhaps was Alameda County's rodent-poisoning program. From 1997 - 2004, rodent poison was scattered throughout the Altamont wind-farm area by the county with funding from the wind industry. The county implemented this program without any Environmental Impact Report or negative declaration. Industry sources say the program has been discontinued, but at the High Winds wind farm in Solano County, this is currently a certified mitigation measure.

The premise for the rodent poisoning program was that a reduction in prey species would discourage raptors from using the area, thus terminating the usefulness to raptors of this essential habitat. Ironically, that objective would prove just as harmful to raptor populations. Recent studies indicate that the result of the poisoning program was in fact an increase in raptor mortality.

In addition, the impacts of anti-coagulant poison on non-target species have likely been substantial. Ingestion of poison or poison-contaminated rodents is lethal to species including badger, fox, coyote, bobcat, and San Joaquin kit fox. Special-status species such as California red-legged frog and tiger salamander may also have been harmed, as they depend on rodent burrows for nesting or cover.

Research results by Smallwood and Thelander suggest far more effective mitigations for reducing mortality at wind farms. These should be implemented - along with precise scientific monitoring and a plan to respond quickly if high mortality continues.

The Sierra Club strongly supports use of wind as a renewable energy source - but we must be determined to utilize it without such costs to our wildlife.

Terry Preston, wildlife biologist and Chapter wildlife chair