Abstract
Biodiversity conservation is a challenge in landscapes increasingly dominated by built structures. When structures such as power lines become barriers to movement among habitat patches necessary for survival, ecological processes may be disrupted. I evaluated the movement of birds flying among complementary habitats separated by a built structure (a power line) with varying degrees of visibility. I tested whether increasing the visibility of the built structure (landscape) facilitated the movement between complementary habitats by comparing the number of fatalities found under control and treatment power lines. I monitored avian collisions with distribution power lines at Staten Island (Walnut Grove, CA) over three winter seasons from 2003 to 2006. The objectives of this study were to 1) estimate avian collisions, 2) evaluate the effectiveness of an aerial marking device (diverter) for reducing avian collisions, and 3) make recommendations to reduce collision risk with these power lines. If birds collide with power lines because they are unable to see them, then increasing power line visibility by marking them with diverters may reduce the number of avian collisions. In order to estimate avian collisions, I conducted carcass counts 3 times per week from November-February. Carcass surveys were conducted under power line spans both pre and post diverter installation. Total carcass counts for sandhill cranes were adjusted to account for bias factors.
In order to evaluate the effectiveness of the diverters, I compared mortality and avian behavioral observations at treatment, control, and buffer sections. Mortality comparisons were made from carcass counts beneath the distribution power line. Avian behavioral observations were recorded for birds flying over treatment, control, and buffer spans. Fatalities under treatment lines were reduced by 60%. Avian flight height and reaction distance, however, were not significantly different between treatments, suggesting that bird flight behavior alone may not be a sufficient method for testing diverter effectiveness. Based on these results, study design and protocol recommendations specific to distribution power lines were made; data necessary to increase precision of future avian mortality estimates was identified; land management measures that could help to reduce avian collisions with power lines were recommended.