Abstract
As part of Southern California Edison's (SCE) goal to develop alternate and renewable energy resources, wind energy development is planned for the San Gorgonio Pass Wind Resource Area (Figure 1). This development may encompass as much as 186 km2 and involve the installation of over 32,000 wind turbines (Wagstaff and Brady 1982). The utilization of wind to produce electrical power, although not new, has never been carried out on such a large scale. As a result the environmental hazards of wind turbine generators (WTG's) and the supportive transmission network are relatively unknown.
Two major environmental concerns of wind energy utilization are whether WTG's will affect seasonal movements or other behavior of migratory birds, and whether collisions will result in significant avian mortality. Although the probability of avian collisions with wind turbines is unknown, high levels of mortality from collisions with numerous other man-made structures (TV towers, smoke stacks, light houses, transmission and distribution lines, etc.) have been documented (for a review see Banks 1979). Estimates of avian mortality from collisions with radio and TV towers alone range from 1 to 1.25 million birds per year (Banks 1979, Mayfield 1967).
Few studies are available for developing effective environmental criteria for the San Gorgonio WTG park. Information on the distribution of nocturnal migrants at the lowest altitudes is not currently available and nocturnal migration has not been examined under the unique physical conditions characteristic of the Wind Resource Study Area (WRSA). A further hinderance is a general lack of information on nocturnal bird migration in southern California.
In accordance with its policy to protect the environment while generating and distributing electrical power, SCE has funded a number of studies on birds in the Coachella Valley and surrounding areas since 1979. Prior to spring 1981 these studies concentrated on densities and utilization patterns of diurnal resident and migratory birds. However, as most birds migrate at night (Able 1973, Emlen 1975), the emphasis of research in the WRSA was shifted to nocturnal studies of migratory birds. This research is intended to: 1) gain a thorough understanding of the dynamics of bird migration in the Coachella Valley, 2) provide information necessary for predicting the potential impact to avifauna resulting from wind turbine construction and operation in the WRSA, and 3) develop generic information on bird interactions with WTG's. These studies are only a portion of SCE's long term commitment to environmental research in regards to alternate energy development.
Research on nocturnal migration was initiated in April 1981 and has continued during four migratory periods (spring and fall 1981, spring and fall 1982). Our initial observations were confined to visual sightings on low altitude nocturnal migration. These data provided preliminary estimates of migration magnitude, flight direction, and the influence of wind on migration (McCrary et al. 1981). With the equipment employed during this period (spring and fall 1981), the altitude of nocturnal avian flights could not be determined, an obviously important aspect in evaluating the potential impact of the WTG park on birds. In spring 1982 we incorporated a modified vertical beam radar (see methods) in the nocturnal research which provided essential data on altitudinal distribution of nocturnal bird migration. In this report we summarize spring 1982 bird migration in the WRSA.
Our principal research objectives were to:
- Measure the magnitude of nocturnal migration in the Wind Resource Study Area (WRSA).
- Measure the altitude of nocturnal migration.
- Obtain data on weather conditions (wind speed and direction, temperature, cloud cover, barometric pressure) and determine how these factors influence nocturnal bird migration in the WRSA.
- Evaluate the effects of topography (change in relief, elevation, etc.) on nocturnal bird migration (altitude, flight direction, magnitude, etc.).
- Conduct-experiments on methods for determining the effect of tall structures on bird behavior and mortality.
- Develop a baseline data set (eg. altitude) necessary to predict the influence, if any, of the proposed WTG park on migratory birds.
- Develop recommendations for mitigating the potential effects of the proposed WTG park on migratory birds.