The Altamont Pass Wind Resource Area (APWRA) is located in central California approximately 56 miles (90 kilometers) east of San Francisco (Figure 1-1). Temperature differences between the air of the warmer Central Valley east of Altamont Pass and the cooler marine air from San Francisco Bay cause steady winds of 15–30 miles per hour (25–45 kilometers per hour) to blow across the APWRA, making the area an ideal setting for production of wind energy. Permits have been granted for 5,400 wind turbines, which together had a rated capacity of approximately 580 megawatts (MW), distributed over 37,000 acres (150 square kilometers) of rolling grassland hills and valleys.
The APWRA also supports a broad diversity of resident, migratory, and wintering bird species that regularly move through the wind turbine area (Orloff and Flannery 1992). In particular, diurnal raptors (eagles and hawks) use the prevailing winds and updrafts for foraging, soaring, and gliding during daily movement and migration. Birds passing through the rotor plane of operating wind turbines are at risk of being injured or killed. Multiple studies of avian fatality in the APWRA show that substantial numbers of golden eagles, red-tailed hawks, American kestrels, burrowing owls, barn owls, and a diverse mix of non-raptor species are killed each year in turbine-related incidents (Howell and DiDonato 1991; Orloff and Flannery 1992; Howell 1997; Smallwood and Thelander 2004). Many of these species are protected by both federal and state wildlife regulations.
The numbers of birds killed annually in the APWRA in turbine-related incidents led to substantial controversy, which in September 2005 resulted in the Alameda County Board of Supervisors attaching extensive conditions of approval to use permits for the continued operation of wind power projects. Aimed at achieving major reductions in avian fatalities, these conditions included the establishment of an Avian Wildlife Protection Program and Schedule (AWPPS) and the formation of a Scientific Review Committee (SRC) and a Monitoring Team (MT).
- The AWPPS consisted of several measures and management actions, such as the strategic removal of turbines, strategic turbine shutdowns, and other actions, aimed at reducing turbine-related avian fatalities. The measures and actions taken are described later in this chapter under Management Actions and Repowering.
- The SRC provided expertise on research and monitoring related to wind energy production and avian behavior and safety. To this end, the goals of the SRC were to provide a neutral forum for open dialogue among experts in the field with different perspectives, reach agreement on analysis and interpretation of data, and ensure sound and objective scientific review of avian safety strategies. The SRC advised Alameda County and the power companies on actions to reduce turbine-related avian fatalities including the identification of hazardous turbines for removal or relocation and recommendations for the timing and duration of turbine shutdowns. In addition, the SRC has directed the MT on study design, set study priorities, suggested analyses, and reviewed and commented on reports.
- The MT implemented the avian fatality monitoring program, analyzed data collected, and reported results in keeping with recommendations made by the SRC. Originally composed of three organizations—WEST, Inc., the Santa Cruz Predatory Bird Research Group, and ICF Jones & Stokes—the MT changed several times since its formation. The MT was headed by West, Inc. for the first two years of the monitoring program, then by the Santa Cruz Predatory Bird Research Group until late 2008, when management of the MT was assumed by ICF Jones & Stokes (now ICF International).
In 2007, the AWPPS was modified by a settlement agreement to end litigation against Alameda County that had been initiated by environmental groups. This agreement included a goal to reduce turbine-related fatalities for American kestrel, burrowing owl, golden eagle, and red-tailed hawk (hereinafter referred to as the four focal species) by 50% from an estimate of annual raptor fatalities (referred to as the baseline) generated from data collected during the period 1998–2003 (hereinafter referred to as the baseline study). That original baseline estimate—1,300 raptors per year—was based on the work of Smallwood and Thelander (2004: Table 3-11). However, the baseline estimate of 1,300 raptors in the settlement agreement was an estimate of APWRA-wide annual fatalities for all raptors—it was not specific to the four focal species associated with the 50% reduction in the settlement agreement. The corresponding (i.e., baseline) value for the four focal species was 1,130 fatalities per year.
The primary goal of the avian fatality monitoring program, which ran continuously from October 1, 2005, through September 30, 2014 (hereinafter referred to as the current study or the study), was to assess progress toward achieving the 50% reduction target. Evaluation of the efficacy of management actions and identification of issues and solutions associated with the accurate estimation of total APWRA-wide avian fatalities became necessary ancillary objectives of the monitoring program.
To better reflect the timing of annual movements of birds through the study area and the implementation of management actions, all analyses in this report are presented on the basis of monitoring years, defined as October 1 through September 30, rather than calendar years.