Effects Of Wind Turbine Operation On Butterflies

Data suggest that the wind speeds and patterns associated with operating turbines likely will not create a collision issue with butterflies.


North American Windpower, Vol. 4, No. 1, February 2007

[Reproduced under protection of Fair Use for educational purposes.]

Concerns over potential impacts of wind power development on aerial wildlife have been researched around the world. A considerable amount of research has focused on the effects of wind turbine construction and operation on birds and bats. This article provides an overview of the potential direct and indirect impacts of wind farms on butterflies, a subject that has received little attention previously. A summary follows of information found in a literature and web review as well as first-hand experience.

Butterfly specialists (lepidopterists) from across Canada were consulted for preparation of this article. Although many of the specialists expressed an interest in learning more about the subject, none had heard anything about the issue of wind farms causing butterfly mortality.

Collisions with wind turbines

No specific protocol for assessing butterfly mortalities caused by collisions with wind turbines currently exists in literature. Paul Gipe noted in "Wind Energy Comes of Age" that the North German Academy for Nature Protection examined 11 wind farm sites on the North Sea, measuring the density of insect splatter on turbine blades. This study focused on removal of the food supply for birds, rather than a concern for insects, but the conclusion was that there was a negligible effect on insects. Gipe also noted a study conducted by the U.S. Department of Energy in which honeybees and blowflies were released and filmed to determine their interaction with an experimental wind turbine. This study found that there was little observable impact on the insects.

Little detail regarding typical butterfly flight altitudes is known. Monarch butterfly migration is well studied, and this species has been recorded to fly between 2 meters and 3,350 meters above ground elevation. These flight patterns would bring the butterflies within the blade heights of wind turbines. Similarly, several butterfly species are known to follow shorelines during migration, but other landscape features and their relationships to flight patterns are less well known.

Non-fatality and habitat impacts

• Wind: No literature was found on how wind turbulence from wind turbines specifically affects insect or butterfly behavior. It is possible that butterflies approaching from a downwind direction may be repelled by the wake from the turbine or become trapped in the wake of the downwind vortex created by wind turbines. Butterflies approaching a turbine from an upwind direction likely will be unaffected unless they collide with the turbine.

J.W. Dover and T.H. Sparks, in "The Importance of Shelter for Butterflies in Open Landscapes," examined how wind speed affects the local distribution of butterfly species in open landscapes and concluded that at all of their study sites, butterflies redistributed as wind speed increased.

Wind currents created by turbine blades may be great enough to sweep butterflies away from them before physical collision can occur.

Butterflies likely will not fly near wind turbines when wind speeds are in excess of force five on the Beaufort wind scale -- 30 kilometers per hour (km/h) to 39 km/h [18.6-24.2 mph]. Clearing vegetation may contribute to increased wind speeds at the turbine bases and deter butterflies from occupying the open area around them. However, this is not anticipated to be an issue with facilities in open agricultural lands or meadows.

Duane McKenna, along with several other academics, conducted a study on the mortality of lepidoptera along roadways in central Illinois and observed that as traffic speeds increased, butterfly mortality decreased. At speeds around 86 km/h [53.4 mph] or greater, lepidoptera were observed to be caught in a wind current, which catapulted them over cars instead of colliding with them.

Applying this finding to wind turbines suggests wind currents created by the turbine blades may be great enough to sweep butterflies away from them before physical collision can occur. However, because blade speeds decrease closer to the nacelle, there will be a point at which blade speed decreases to less than 86 km/h.

For example, a typical 1.5 MW wind turbine with a 41-meter blade, moving at a nominal speed of 14.4 revolutions per minute (rpm), has a blade tip speed of approximately 200 km/h. At this rotation speed, blade speed reaches 86 km/h approximately 16 meters from the base of the blade. Based on the findings of McKenna and his colleagues, butterflies would only be in danger of collision with the turbine blade in 15% of the blade [sweep area].

Additionally, because butterflies disfavor conditions that exceed force five on the Beaufort wind scale, the area of possible collision within the blade sphere would decrease to as little as 1.9%. At lesser rpm, the relative amount of the blade sphere that could result in collisions would increase.

• Temperature: Temperature is an important factor contributing to butterfly behavior. In order to fly, butterflies require thermal energy from the sun and a wing temperature of at least 25 degrees C. Therefore, seasonal considerations would be limited, with few concerns in spring and fall, and no concerns in winter. Habitat fragmentation caused by clearing land for wind turbines has the ability to change local climatic conditions. Bengt Karlsson and Hans Van Dyck, in "Does Habitat Fragmentation Affect Temperature-Related Life-History Traits?," examined temperature-related performance in terms of fitness. Using a temperature-gradient experiment, they found that as temperature increased, egg weight and size decreased, resulting in decreased female fecundity.

Consequently, clearing vegetation may increase ground-level temperatures, affecting butterfly host plants as well as their immature stages.

• Habitat Loss: Habitat loss is an important potential indirect impact on butterflies. Butterflies have been observed as being highly habitat-specific and only able to adapt to a narrow range of environmental conditions. They are tied closely to the diversity and health of their habitats because their larvae are dependent on specific host plants, and adults are pollinators of specific nectar plants. Butterflies require certain structural elements for basking orientation and are expected to show a strong response to changes in vegetation.

Few environmental assessments for potential wind farm sites have evaluated butterfly habitat, and in these few cases, the assessments have only examined habitat for sensitive species in the area.

Examples include:

• a study for a proposed wind facility at Vandenberg Air Force Base in California) in which bioresource consultants evaluated the presence of suitable habitat for the monarch butterfly -- a Species of Special Concern in California -- and

• a survey by Lawrence Environmental Consultants on suitable invertebrate habitat for selected target species (three butterflies and one moth) of important local species at a proposed wind farm site in the U.K.

These reports concluded that no significant impacts on the butterflies were expected.


It is well known that monarchs will follow shorelines while migrating south from eastern Canada. They fly and roost in large numbers along the shores of Lake Erie and other large bodies of water every fall. The implications of other landscape features, such as ridges, are less well known. This may be an important consideration when selecting turbine sites. Currently, however, there is no evidence to suggest that butterfly mortality is a concern at commissioned wind farm sites as a result of collisions with turbines.

Although not directly researched, findings of other studies on butterflies have provided data that suggest the wind speeds and patterns associated with operating turbines likely will not create a collision issue with butterflies. Butterfly mortality at wind farms may become an emerging issue of concern in the future, especially for locally rare or sensitive species.

Jessica Grealey is a terrestrial and wetland biologist for Waterloo, Ontario-based Natural Resource Solutions Inc. (NRSI), an environmental consulting firm (www.nrsi.on.ca). Grealey can be reached at 519.725.2227 or by e-mail at jgrealey@nrsi.on.ca. David E. Stephenson is a senior biologist at NRSI. Stephenson can be reached at stephenson@nrsi.on.ca.