Population Study of Golden Eagles in the Altamont Pass Wind Resource Area: Population Trend Analysis, 1994-1997

摘要

The wind industry has annually reported 28-43 turbine blade strike casualties of golden eagles in the Altamont Pass Wind Resource Area, and many more carcasses have doubtless gone unnoticed. Because this species is especially sensitive to adult survival rate changes, we focused upon estimating the demographic trend of the population. In aerial surveys, we monitored survival within a sample of 179 radio-tagged eagles over a four-year period. We also obtained data on territory occupancy and reproduction of about 65 eagle pairs residing in the area. Of 61 recorded deaths of radio-tagged eagles during the four-year investigation, 23 (38%) were caused by wind turbine blade strikes. Additional fatalities were unrecorded because blade strikes sometimes destroy radio transmitters. Annual survival was estimated at 0.7867 (SE=0.0263) for non-territorial eagles and 0.8964 (SE=0.0371) for territorial ones. Annual reproduction was 0.64 (SE=0.08) young per territorial pair (0.25 per female). These parameters were used to estimate population growth rates under different modeling frameworks. At present, there are indications that a reserve of non- breeding adults still exists, i.e., there is an annual territorial reoccupancy rate of 100% and a low incidence (3%) of subadults as members of breeding pairs.