Study estimates 18.7 million bat deaths at US wind farms since 1981

What you need to know

• The study’s median estimate is 18.7 million fatalities, with a 95% credible interval of about 13.3 million to 25.7 million. This range reflects uncertainty in the modelled total, rather than a count of observed carcasses. 13
• Four species account for most of the estimated deaths: hoary bats, at about 6.7 million; eastern red bats, 5.8 million; silver-haired bats, 3.4 million; and big brown bats, 1.5 million. 1
• The model estimates more than 1.5 million fatalities annually from 2021. This is a modelled annual estimate, not a verified tally for each year. 1
• Larger rotor-swept areas, lower ground clearance and closer proximity to rivers were associated with higher fatalities for multiple species. The study reports correlations, which do not establish that these features caused the higher totals. 1
• The data release provides species-specific relative fatality risk maps across the contiguous United States. These may help identify patterns for further assessment, but the sources do not establish that any particular mitigation measure has reduced fatalities in practice. 34

Why this matters

The estimate points to substantial wildlife mortality associated with onshore wind energy, while showing how much remains uncertain about its consequences. Understanding where risk is concentrated and whether it affects population trends is important for judging the conservation implications and potential responses. 134

What happens next

The reporting identifies population-level assessment, more standardised and higher-resolution monitoring, and tests of species-specific siting or operational measures as unresolved needs. It does not establish which measures work, or what trade-offs they might involve. 14

What we know

• The analysis pooled 499 post-construction monitoring reports and modelled fatalities for ten bat species. 13
• Its geographic coverage is the contiguous United States, and its cumulative estimate spans 1981 to 2024. 13
• The collected sources agree on the central estimate and its main qualification: it is based on monitoring data and modelling, not a complete direct count. 124

What we don't know

• The study does not resolve how the estimated fatalities affect population trends or viability for each of the ten species. 14
• The available reporting does not establish whether more standardised, higher-resolution monitoring would materially change national or species-level estimates. 14
• It remains unclear which species-specific siting or operational measures reduce fatalities in practice, and what trade-offs with energy production they may involve. 14

Read the reporting

This WildNews briefing synthesises and summarises reporting from the sources below. WildNews did not produce the original reporting. Learn more about how we use AI