Bird and Bat Movement Patterns and Mortality at the Montezuma Hills Wind Resource Area - Final Project Report

Publication Number:    CEC-500-2013-015

Abstract:

Birds and bats have become important factors in the siting and permitting of wind‐energy facilities. Identifying methods to avoid, minimize, and mitigate bird and bat fatalities should help streamline wind energy permitting and reduce potential impacts to bird and bat resources. In this study, the authors conducted nighttime surveys to investigate the effectiveness of using horizontal/vertical radar, full‐spectrum acoustic monitoring and night vision to determine nocturnal flight directions, passage rates, and flight altitudes of birds and bats at the Montezuma Hills Wind Resource Area in Northern California. Following nighttime surveys, daily carcass searches were conducted to assess fatality rates as a function of movement patterns in the wind resource area. In addition, the study explored relationships between bird and bat fatalities, relevant activity indices, and the meteorological, landscape, and vegetation features of the study area.

Although average nocturnal passage rates ranged from 326—454 targets per kilometer per hour, a high rate in the western United States, only 2–6 percent of the total passed through at altitudes less than the 125 meters above ground level, the height where birds and bats are at risk of collision with wind turbines. Six nocturnal‐migrant bird and 53 bat fatalities were observed during the two 40‐day surveys. Carcass‐detection ratios ranged from 0.20–0.50. Carcass‐removal rate analysis indicated that 45 percent of small bird and 39 percent of bat carcasses disappeared within 24 hours, suggesting that a majority of small bird and bat fatalities would be missed by the weekly surveys that are commonly conducted. The total number of nocturnal migrant bird fatalities was quite low relative to the passage rate, indicating that this wind resource area is relatively benign with respect to migrating birds.

Overall, the three detection methods (radar, night‐vision, and acoustic) helped to provide a comprehensive and detailed view of the species inhabiting the night skies over the study area. In particular, this study identified that using altitude‐specific radar in the high‐risk zone can be a useful tool for monitoring fatality risk for birds in this wind resource area.

Author(s):  Dave S. Johnston, Judd A. Howell, Scott B. Terrill, Nellie Thorngate, Jim Castle, Jeff P. Smith

Commission Division:    Energy Research and Development (500)

Office/Program:    PIER: Public Interest Energy Research

PIER Program Area:    Energy-Related Environmental Research

Date Report Completed:    June 2013

Date On Line:    07/08/2013

Acrobat PDF File Size: 140 pages, 3400 kilobytes