Abstract
This report aims to provide the most up-to-date understanding of the patterns and variability in species composition, timing, and magnitude of bird collisions with land-based wind energy turbines to support research and insight. Findings are useful in checking assumptions and setting expectations about collision risks at wind energy facilities, as well as generating testable hypotheses.
Background
This report summarizes data from 331 post-construction mortality monitoring studies conducted over 21 years and across 254 land-based wind energy projects in the United States.
- The AWWIC database contains fatality estimates and protocols used to develop those estimates, individual fatality incident records, and information about the wind energy project itself (such as turbine size, installed capacity, ecoregion).
- Most studies and search data represented in AWWIC are from the Prairie avifaunal biome, which contains 70% of installed wind energy capacity in the U.S.
Carcass detection insights
- Approximately 60% of carcasses were found within 50 m and 80% were found within 80 m when searches extended at least 100 m from the turbine. No difference observed in fall distance distribution between large and small birds.
- Full plot searches provided much greater density weighted proportion (DWP) for both small and large birds (median 0.89 and 0.88, respectively) than road-andpad searches provided (median 0.14 and 0.10, respectively).
- Large bird carcasses persisted on the landscape longer than small birds (6.7 vs. 4 days on average) and were more likely to be found by surveyors than small bird carcasses (90% vs. 67%).
Insights regarding bird fatalities
- Bird fatality incidents were rare, but widespread: Nearly all (98%) studies report at least 1 bird fatality, yet 98.1% of turbine-searches found zero carcasses.
- Estimated bird fatality rates differed greatly among studies: Many had low fatality estimates and few had high values. Median fatality estimates were similar across avifaunal biomes (regions).
- The median fatality estimate for all birds in the U.S. is 1.9 birds per MW per year and 3.9 birds per turbine per year. Only 13% of studies estimated fatalities >5 birds per MW per year.
- Birds of conservation concern rarely occurred as fatality incidents, and no U.S. bird species with federal threatened or endangered status were recorded as fatalities.
- Bird species with “tipping point” status in 2025 State of the Birds (NABCI 2025) accounted for 1% of total fatality incidents (110) from 24 species. Four of those species are categorized as “Red Watch List” and each accounted for 4 or fewer fatality incidents.
- A small number of common U.S. bird species make up most fatality records.
- 44% (314) of the 719 bird species occurring in the U.S. (Partners in Flight 2024) have been recorded as collision fatalities found during scheduled turbine searches in AWWIC. A third (110) of the recorded species are represented in the database by only one or two incidents.
- Sixteen common bird species accounted for nearly half (47.5%) of the fatalities recorded in AWWIC. These species are common, particularly in the Prairie avifaunal biome where most wind energy projects operate.
- Small passerines accounted for 59% of all bird fatality incidents in AWWIC across all avifaunal biomes, with Horned Larks making up the greatest species percentage (13%).
- Diurnal raptors accounted for 6.8% of total fatality records nationwide ranging regionally up to 8.5% in the Pacific biome, though small passerines remained the highest reported group for this biome.
- Bird fatalities for passerines nationally and for all birds in most biomes peaked during spring and fall (in alignment with peak migration periods). However, no seasonal pattern was apparent for raptors nationally or for all birds in the Northern Rockies and Pacific biomes.