It is still unknown how most species react to wind turbines. Moreover, the difference in reactions amongst species is great. Detecting an influence is also dependent on research methods and questions. For example, in red deer¹ (Cervus elaphus), reindeer² (Rangifer tarandus) and ground squirrels³ (Marmotini) no significant avoidance behavior can be detected. However, closer investigation into the behavior of ground squirrels shows that animals living in the area of wind farms, in comparison to those living outside of them, react differently to calls from conspecifics³.
Just as collisions with wind turbines have been confirmed in birds⁴, they have also been confirmed in bats⁵'⁶. It has even been shown that bats can suffer lethal barotrauma from the air pressure differences near moving rotor blades⁷'⁸'.
Furthermore, birds are known to collide with wind turbine towers, as well as the blades⁹. However, the level of risk is not the same for every bird species¹⁰. Larger, less agile birds (e.g. geese and swans) or birds with certain behavioral patterns, such as those which make use of thermal updrafts for ascension (e.g. raptors), collide more commonly with wind turbines¹¹'¹²'¹³'¹⁴.
In most cases, the influence of collision mortality on populations is unclear. In Belgium, it was confirmed for a colony of terns (Sternidae) that collisions with wind turbines had a negative effect on the local population. However, whether or not there was a significant effect on the overall population could not be determined¹⁵.
Many birds avoid flying through wind farms, possibly disturbing their dispersal and population connectivity¹⁶'¹⁷'¹⁸'¹⁹. The “scare effect” of wind turbines on birds is little understood. This term refers to the diminished occurrence of a species in an area with wind turbines, in comparison to an area without wind turbines. On the one hand, this can be caused directly through the presence of turbines (e.g. shadows cast from rotor blades, noise caused by turbines). On the other hand, the construction of a wind turbine or wind facility can also have an indirect influence on the habitat of animals. For example, through the construction of new or replacement forest roads built to access wind energy sites, a resulting increase of human use (e.g. hikers and mountain bikers) often occurs, which can act as an additional disturbance to sensitive wildlife¹⁰'¹⁷'²⁰'²¹.
Various bird species were determined to use the area around wind turbines less, or to occur there in lower densities¹⁷. However, differences have been observed between species, habitats, seasons, and even between different locations²²'²³.
¹ Walter et al. (2006): Response of Rocky Mountain elk (Cervus elaphus) to wind-power development
² Flydal et al. (2004): Effects of wind turbines on area use and behaviour of semi-domestic reindeer in enclosures
³ Kikuchi (2008): Adverse impacts of wind power generation on collision behaviour of birds and anti-predator behaviour of squirrels
⁴ Drewitt & Langston (2008): Collision effects of wind-power generators and other obstacles on birds
⁵ Rydell et al. (2010): Bat Mortality at Wind Turbines in Northwestern Europe
⁶ Kuvlesky et al. (2007): Wind Energy Development and Wildlife Conservation: Challenges and Opportunities
⁷ Baerwald et al. (2008): Barotrauma is a significant cause of bat fatalities at wind turbines
⁸ Grodsky et al. (2011): Investigating the causes of death for wind turbine-associated bat fatalities
⁹ Johnson et al. (2002): Collision mortality of local and migrant birds at a large-scale wind-power development on Buffalo Ridge, Minnesota.
¹⁰ Langston & Pullan (2003): Windfarms and birds: an analysis of the effects of wind farms on birds, and guidance on environmental assessment criteria and site selection issues
¹¹ Orloff & Flannery (1993): Wind turbine effects on avian activity, habitat use, and mortality in the Altamont Pass and Solano County Wind Resource Areas. In: Huckabee J.W. (ed.), Avian Interactions with Utility Structures.
¹² Osborn et al. (1998): Bird flight characteristics near wind turbines in Minnesota
¹³ de Lucas et al. (2008): Collision fatality of raptors in wind farms does not depend on raptor abundance
¹⁴ Garvin et al. (2011): Response of raptors to a windfarm
¹⁵ Everaert & Stienen (2007): Impact of wind turbines on birds in Zeebrugge (Belgium)
¹⁶ Langston & Pullan (2004): Effects of wind farms on birds
¹⁷ Drewitt & Langston (2006): Assessing the impacts of wind farms on birds
¹⁸ Fahrig (2003): Effects of habitat fragmentation on biodiversity
¹⁹ Farfán et al. (2009): What is the impact of wind farms on birds? A case study in southern Spain
²⁰ Gill et al. (1996): Review of the impacts of windfarms and other aerial structures upon birds
²¹ National Research Council (2007): Environmental impacts of wind-energy projects
²² Steward et al. (2007): Poor evidence-base for assessment of windfarm impacts on birds
²³ Pearce-Higgins et al. (2009): The distribution of breeding birds around upland wind farms