Abstract
The development of alternate energy technologies has long been a goal of the Southern California Edison (SCE). These technologies--wind, solar, and geothermal--have been planned for specific areas in southern California . The development of these energy resources, especially wind and solar, require the use of extensive land areas. A large scale wind energy development is planned for the San Gorgonio Pass and Coachella Valley areas of Riverside County (Figure 1). This development may encompass as much as 186 km2 and could involve the installation of up to 32,000 wind turbine generators (WTG) (Wagstaff and Brady 1982). Along with SCE's goal to develop and distribute alternate energy resources, there is a commitment to protect the environment in relation to each energy-related development. Therefore, this environmental concern by SCE prompted an investigation of the biological impact of wind energy development in the San Gorgonio Pass and Coachella Valley.
In 1979, SCE funded a study to gather baseline information to gain a better understanding of the dynamics of migratory and resident bird utilization of the San Gorgonio Pass and adjacent desert areas. This was initiated because of the highly land consumptive nature of wind energy development which could affect critical migratory and resident bird habitats. Other concerns with this new technology are whether WTG's could interfere with seasonal movements of migratory birds, their ecology and/or behavior, and possibly result in significant bird deaths due to collisions.
Bird distribution of southern California, in general, has been thoroughly examined by both Grinnell and Miller (1944) and Garrett and Dunn (1981). However, the details of species distribution, migration, and population densities along with habitat utilization are poorly documented. Specific locations, such as the San Gorgonio Pass-Coachella Valley region, are essentially unknown. While some anecdotal sightings of birds in this region have been made over the years, prior to this study, no systematic survey has been conducted.
Historically, several ornithologists postulated on bird migration and usage in the California deserts. Miller (1951) noted "each year across the deserts of the lower Colorado River basin of the southwestern United States and northwestern Mexico move great numbers of migrant birds, passing between their mesic or even humid and cool breeding grounds and the wintering ranges in the mountains or mesic areas of the mainland of Mexico." Jehl (1977) states migrants wintering in Baja California pass through the desert areas to breeding areas in the Great Basin and beyond. Shorebirds and waterbirds that winter along the Pacific Coast of California or Mexico, or at the Salton Sea, cross the area in several directions while returning to inland breeding colonies in the central United States and prairie provinces of Canada. The most extreme of these trans-desert movements requires a flight of 804-1,126 km (500-700 miles) across terrain that is largely unsuitable for the survival of most species. And in fall, especially. the movement is made all the more rigorous by hot and dry conditions of that period. The route that Jehl refers to is the region between the Pacific slope (west of the transverse range) and the highland of west Mexico in the State of Sonora.
Lying between these two localities are two regions, the San Gorgonio Pass and Coachella Valley, which have been identified as major routes of migration. Howell (1923) considered that the shores of the Salton Sea basin provided leading lines for migrants northward to the Coachella Valley. Small (1975) postulated that, of the five California deserts, the Colorado Desert (Coachella Valley and Imperial Valley) figures most importantly in the spring migratory patterns of birds into California from Mexico.
The influence of topography on migrants has also been considered by Miller (1951) in his review of "Avian flyways of Western America." He discusses the importance and effects of topography, especially fault lines and mountain passes, in directing migration. He also considered the route from the Gulf of California through the Coachella Valley and San Gorgonio Pass to be the major route of birds crossing the desert.
With these historic perspectives defined, r2search in the San Gorgonio Pass and Coachella Valley was initiated in March 1979 and continued for four diurnal migratory periods (spring and fall 1979 and spring and fall 1980). The spring 1979 field season was considered preliminary in nature and involved study site and methodology evaluations. These data from the spring 1979 season, although not interpreted in this report, clearly indicated the need for a more extensive biological study of the region; therefore, we conducted more systematic studies in fall 1979 and spring and fall 1980.
The objectives of this study were to:
- Collect baseline information on the extent of use of migratory and resident birds within and adjacent to the wind resource study area (WRSA).
- Determine and evaluate seasonal trends.in spring and fall bird migration.
- Obtain data on habitat utilization and identify high-use areas within or near the WRSA.
- Complement further nocturnal avian studies with a baseline data set of diurnal observation of species compositions and numbers of migrant birds.
- Develop recommendations for mitigating the potential effects of the WTG park on migratory and resident birds.