Alameda, Contra Costa, and Solano counties sponsored a two-year study that was funded by the California Energy Commission and conducted by BioSystems Analysis, Inc. The purpose of the study was to evaluate the extent and significance of the impact of wind turbines on birds, to identify the causes and factors contributing to bird deaths, and to recommend mitigation measures. The study was a cooperative effort among county governments, state agencies, and the windfarm industry. This report presents the results of our study.
The study areas included the Altamont Pass Wind Resource Area (WRA) in Alameda and Contra Costa counties and a WRA under development in Solano County. The Altamont Pass WRA is the largest wind turbine development in the world. At present, over 7,000 turbines catch the wind blowing across the open grasslands and rolling hills of the Altamont Pass. Both study areas provide important foraging habitat for at least 13 species of resident and migrating hawks, eagles, and vultures. Because Solano County had no developed windfarm sites when the study began, most of the data were gathered in Altamont Pass. All mortality data were collected in the Altamont Pass WRA.
We conducted six seasons of field work (1989-1991) within the Altamont Pass. Our study included searching the ground near turbine and transmission line structures for injured or dead birds, measuring the rate of bird carcass removal by scavengers, assessing the ability of observers to locate bird carcasses, determining the relative abundance of birds in the area, and observing bird behavior in relation to the turbine and transmission line structures.