Wind energy is increasingly being used as a renewable energy source around the world. However, there have been concerns about the impact of wind turbines on birds and other wildlife. One of the main concerns is that birds may collide with wind turbine blades, leading to injury or death. So what do we know about bird mortality rates caused by wind turbines?
How many birds are killed by wind turbines each year?
According to estimates from the U.S. Fish and Wildlife Service, between 140,000 and 500,000 birds are killed annually by wind turbines in the United States. However, the number varies considerably by location. Some wind energy facilities report hundreds of bird fatalities per year, while others report zero.
There are a few factors that influence bird mortality rates at wind facilities:
- Number and size of turbines
- Turbine design and lighting
- Landscape features and habitat
- Type of birds in the area
- Season and weather patterns
In general, larger wind facilities with more turbines are linked to higher bird mortality. The design of turbines, such as rotor speed, and lighting systems also plays a role. Facilities located in areas with a high diversity of birds or along migratory flyways may see higher fatalities.
How does this compare to other human-related causes?
While the number of birds killed by wind turbines may seem high, it represents only a fraction of total bird deaths caused by human activities. In the U.S., the major human-related threats to birds, in order of magnitude, are:
- Collisions with buildings and windows: 600 million to 1 billion bird deaths per year
- Collisions with vehicles: 200+ million
- Collisions with transmission lines: up to 174 million
- Poisoning by pesticides and other chemicals: 72 million
- Collisions with communication towers: up to 50 million
- Oil and wastewater pits: 750 thousand to 1 million
- Wind turbines: 140,000 to 500,000
Scientists estimate the total annual bird deaths from human activities in the U.S. to be between 1 and 3 billion. Wind turbines are responsible for less than 0.05% of that, according to the U.S. Fish and Wildlife Service estimates. Activities like building collisions and cats pose a much bigger threat.
What types of birds are most affected?
There are certain groups of birds that tend to have higher mortality rates around wind turbines than others:
- Raptors such as eagles, hawks, and falcons. Their hunting habits make them more susceptible.
- Migratory songbirds such as warblers and thrushes. Turbines along migratory flyways impact these birds.
- Wetland birds like waterfowl and shorebirds. Turbines near wetlands areas pose a greater collision risk.
- Nocturnal birds such as owls and nightjars. Turbine lights can attract them.
- Flocking birds like European starlings. Flocks increase collision risk.
There can be regional differences too. For example, gulls and terns suffer higher mortality rates at wind facilities in the Great Lakes areas. Vultures account for most wind turbine deaths in the southeastern U.S. Overall, passerines (perching birds) make up the majority – 70% – of documented turbine-related fatalities.
What are the impacts on threatened and endangered bird species?
There is particular concern about the impacts of wind energy development on threatened and endangered bird populations. Some examples:
- Golden eagles – At risk from turbine collisions, especially in western states.
- Whooping cranes – Collisions and habitat loss concerns along migration route.
- Red knots – Proposed wind projects along migratory routes on east coast.
- Greater sage-grouse – Avoidance of turbines could impact breeding habitat.
- Roseate terns – Collision risk from offshore wind facilities along Atlantic coast.
However, research shows that most threatened and endangered bird species suffer relatively low mortality rates from wind turbines, at least in comparison to other collision and habitat threats they face. Still, extra precautions are warranted for siting wind projects in sensitive areas.
What tactics can reduce bird deaths from wind turbines?
There are a number of strategies and technologies that can help reduce risks to birds from wind energy facilities:
- Proper siting to avoid key wildlife areas and migration routes.
- Using tubular towers instead of lattice-type towers to reduce perching and nesting.
- Minimizing lighting on turbines or using blinking lights rather than fixed illumination.
- Using UV coatings on blades to make them more visible to birds.
- Slower rotor speeds to reduce collision impacts.
- Automatic curtailment of turbines when birds are most active.
- Retrofitting power lines for underground burial.
Turbine technologies continue improving, and learning where and when to site wind projects provides the clearest benefits for birds.
Conclusion
In summary, while wind turbines do lead to some bird deaths each year, the mortality rates are relatively low compared to other human-related threats that birds face. Proper siting and design of turbines can help reduce risks to birds. Overall, wind energy represents a small fraction of total human-caused bird fatalities, which are estimated to be between 1 to 3 billion birds annually in the U.S. Other issues like building collisions and cats pose a much greater threat to bird populations than wind turbines.