We detected powerline collisions in every region of Kaua'i, in every environment type, and at all powerline heights monitored. Forty-three percent of observed collisions occurred at unsearchable powerlines (mainly spanning steep valleys), equating to an estimated 3170 seabird collisions that could not be detected through ground searches. Furthermore, observed collision rates were significantly higher at powerlines that had very low to zero searchability. Environmental bias resulted in significant reductions in searchability across regions, environment types, and powerline heights.
We tested environmental bias by comparing our ability to conduct searches for grounded birds, "searchability", across multiple variables. This means that traditional ground searches would underestimate total collisions by 78-88% if not accounting for crippling bias. While some collisions resulted in birds falling lifelessly out of the sky, most resulted in seabirds flying or gliding outside of the search area. We directly observed 121 powerline collisions and detected 89 grounded seabirds. From 2012 to 2020 we conducted observations for seabird powerline collisions across Kaua'i, documented grounded seabirds, and assessed crippling and environmental biases - both poorly studied facets of powerline collision research. Powerline collisions have been identified on Kaua'i as a potential contributing factor to the large-scale decline of both Hawaiian Petrel ( Pterodroma sandwichensis) and Newell's Shearwater ( Puffinus newelli), but the scale of the powerline collision problem is unknown. Powerline heights and environment type at collision locations.Searchability at powerlines with confirmed collisions, collision rates, and collision numbers.Immediate short-term collision outcome & max crippling bias.
Total observed seabird powerline collisions.Observed collision rates and estimated collision numbers.Environmental bias and powerline searchability.1Archipelago Research and Conservation, 2Kauai Endangered Seabird Recovery Project, Pacific Cooperative Studies Unit, University of Hawaii, 3State of Hawaii Division of Forest and Wildlife, 4University of Wisconsin-Madison, 5Department of Biology, University of Hawaiʻi at Mānoa, Honolulu, HI, 6Save Our Shearwaters, Kauai Humane Society