Wildlife, Energy & Community Coalition
Wildlife
Migratory Bird Collision Risk From Wind Turbines and Transmission Lines
Wind turbines and transmission lines both pose collision risks to birds, but the mechanisms and the affected species are not identical. Understanding the difference matters when reviewing a project's wildlife impact analysis.
Turbine blade tips can move fast enough that birds have little time to react, especially at night or in poor visibility. Transmission lines pose a different risk, largely from birds failing to see thin wires against open sky, particularly near wetlands and other stopover habitat.
Location Matters More Than Technology Type
A wind facility sited along a major migratory flyway carries a fundamentally different risk profile than one sited outside major flight paths. The same is true for transmission corridors near wetlands, lakes, or river valleys that concentrate bird movement.
This is why siting review should weigh documented flyway data, not just generic regional bird counts.
Species Vary Widely in Vulnerability
Raptors, which spend more time soaring and scanning the ground than watching directly ahead, are disproportionately represented in turbine collision studies at certain sites. Waterfowl and other flocking species face elevated risk from transmission lines near their flight paths between roosting and feeding areas.
A single collision estimate for "birds" as a category obscures which species are actually being affected, and by how much.
What Reduces Risk in Practice
- Siting turbines and lines away from documented flyways and stopover habitat
- Marking transmission lines with visibility devices in high-risk segments
- Curtailing turbine operation during peak migration windows at high-risk sites
- Conducting pre-construction surveys long enough to capture seasonal variation
Watch for Thin Pre-Construction Survey Periods
A survey conducted over a few weeks cannot capture the full picture of seasonal migration through a site. Multi-season surveys are more reliable, and their absence is worth flagging in public comments.
If a project's environmental review relies on a single season of bird survey data, ask why longer-term data was not collected or considered.
Post-Construction Monitoring Is Often the Missing Piece
Even a well-sited project benefits from monitoring after construction to confirm that predicted collision rates match reality. Many proposals include monitoring requirements on paper without clear funding or enforcement behind them.
Ask specifically who conducts post-construction monitoring, how often, and what happens if collision rates exceed what was predicted.
Cumulative Risk Across Multiple Projects
A single turbine array or transmission segment might carry an acceptable individual risk, but the same flyway can host multiple projects over time. Cumulative collision risk across all nearby infrastructure is the number that actually matters to a bird population, not any one project in isolation.
This is one of the areas where community documentation, tracked over years, becomes especially valuable to regulators and researchers alike.