Sunita Somvanshi
New research from Cornell University reveals important patterns in how birds migrate over coastal waters, offering practical ways for offshore wind farms to reduce bird deaths while still producing clean energy.
The study, published in the Journal of Applied Ecology, analyzed 10 years of weather radar data from 16 sites along the Atlantic coast and Gulf of Mexico. Researchers discovered that offshore bird migration happens in shorter, more intense bursts compared to migration over land, and birds fly 13-20% lower over water than over land.
“Offshore migration takes place in fewer nights than terrestrial migration because birds may be more selective about when to migrate over water,” explained Shannon Curley, lead author and postdoctoral fellow at the Cornell Lab of Ornithology.
“Large bodies of water lack places to rest and refuel, so birds may wait for ideal weather conditions, such as favorable winds, before making an offshore crossing.”
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This finding creates a potential opportunity for wind farm operators. By pausing turbines during these concentrated migration periods, millions of birds could be protected with minimal impact on energy production.
Adriaan Dokter, a co-author and research associate at the Cornell Lab of Ornithology, noted this timing advantage: “These peak nights of migration tend to have fairly nice weather and calmer winds, and are therefore not the nights when wind operators have a huge energy harvest. So there might be a sweet spot where we can target these big migration nights and give these birds safe passage, with limited loss of energy.”
European wind farms are already pioneering these bird-friendly approaches. In the North Sea, operators use “start/stop” curtailment systems that temporarily shut down turbines during peak migration periods.
These advanced monitoring systems combine weather radar forecasts with thermal cameras and AI tracking mounted on turbines or buoys. This technology helps operators know exactly when birds are approaching and when to pause operations.
The Cornell study also found seasonal differences in migration routes, with more birds crossing the western Gulf of Mexico in spring and the eastern portion in fall. Fall migration involves more birds than spring migration, including young birds making their first journey south.
While land-based wind turbines cause between 140,000 and 327,000 bird deaths annually in the U.S., the number of deaths at offshore sites remains unknown because recovering bird carcasses at sea is extremely difficult. This makes radar monitoring particularly valuable for identifying high-risk areas.
The findings come at a critical time. According to the U.S. State of the Birds report, one-third of all American bird species are rapidly declining. Meanwhile, offshore wind energy development continues to expand as part of efforts to reduce carbon emissions.
Conservation groups like Audubon have proposed a four-step approach: avoid critical habitats, implement minimization measures like curtailment, offset unavoidable impacts, and monitor before and after installation.
The Gulf of Mexico presents special challenges as it funnels hundreds of millions of migratory birds annually and faces active leasing for wind development.
Researchers recommend specific studies of flight heights during bad weather and shore-parallel movements in this critical region.
“Our hope is that this work will help identify high-risk, high-use areas for birds and work towards positive green energy solutions,” Curley said.
The research team included scientists from the Cornell Lab of Ornithology, the U.S. Bureau of Ocean Energy Management, and the University of Amsterdam.
