Radar technology may help design raptor-proof wind farms in the future

In this post, Miguel Ferrer and Des Thompson discuss the recently published paper by Sergio Cabrera-Cruz and Rafael Villegas-Patraca ‘Response of migrating raptors to an increasing number of wind farms

This study has for the first time used radar trajectories of more than 3.7 million migrant raptors, over six years, to measure responses to a wind farm. Essentially, in an experimental situation of pre- and post-wind farm construction periods, the study has shown raptors detected the presence of turbines and apparently avoided them by changing flight direction. Because of this, the mortality of migrants at this wind farm was practically non-existent.

In previous studies at other important migratory points, notably the Gibraltar Strait in south Spain (de Lucas, Janss & Ferrer 2004), birds showed avoidance behaviour, but came close to the turbines, a behaviour that has been termed ‘micro-avoidance’ (Marques et al. 2014). On the other hand, flight trajectories which change in order to avoid entering a wind farms are termed ‘macro-avoidance’ (Marques et al. 2014); this has been documented at offshore wind farms for marine birds (Dirksen, Winden & Spaans 1998; Christensen et al. 2004; Desholm & Kahlert 2005; Masden et al. 2009; Plonczkier & Simms 2012). But, until the publication of this new research, we had little evidence for the same behaviour for migrating raptors at onshore wind farms.

Red-shouldered hawk taking flight
Photo by Gouldingken – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=37791449

Although birds can avoid turbines, long lines of turbines have a potential barrier effect (Dirksen et al. 1998). The magnitude and effects of these passageway changes in flight direction needs more research. Critically, we need far more work on pre- and post- construction periods to understand consequences for bird populations.  It is imperative that new wind power developments are placed in locations of relatively low risk to birds. Specific locations should be evaluated before a wind farm is planned.

Now, thanks to this paper, we know that the intuitive idea of a migratory point with huge passages of birds being life-threatening does not hold.  Instead, migrants are able to detect then avoid the turbines, decreasing risks of collision. Of course low risks of collision may have been related to the fact that the area is used as a passageway, but not at lower altitude feeding, roosting or breeding area flights. That’s why we need more work to develop the findings here.

Turkey Vulture (Cathartes aura)
Photo by Marlin Harms – http://www.flickr.com/photos/marlinharms/5662909253/.

Wind farms spawn many power lines, and these are a more important cause of bird deaths (Janss & Ferrer 1999), especially because of the massive extent of the many power line networks. Erickson et al. (2001) estimated that 750,000–1,000,000 birds were killed annually by collisions with power lines in The Netherlands, and 130–174 million birds per year in the United States may be killed in this way. Ferrer et al. (1991) estimated that 400 raptors per year were killed along 100 km of power lines within and around Doñana National Park, in south western Spain, with collisions an important cause of death (Janss & Ferrer 1999).  Before the wind farm is constructed (the pre-construction phase), potential effects of associated power lines must be studied to reduce their impacts on birds.

Of course, migratory birds which avoid turbines may pay other costs, not least in extending the duration and length of their journeys, and this still needs to be analysed.


Christensen, T.K., Hounisen, J.P., Clausager, I. & Petersen, I.K. (2004) Visual and radar observations of birds in relation to collision risk at the Horns Rev offshore wind farm. Annual status report 2003. 48 pp.

Desholm, M. & Kahlert, J. (2005) Avian collision risk at an offshore wind farm. Biology letters, 1, 296–8.

De Lucas, M., Janss, G. F., & Ferrer, M. (2004). The effects of a wind farm on birds in a migration point: the Strait of Gibraltar. Biodiversity & Conservation, 13(2), 395-407.

Dirksen, S., Winden, J. vad der & Spaans, A.L. (1998) Nocturnal collision risks with wind turbines in tidal and semi-offshore areas. in Energy and Landscape (eds Ratto & Solari), 99–108. Rotterdam.

Erickson, W. P., Johnson, G. D., Strickland, M. D., Young Jr, D. P., Sernka, K. J., & Good, R. E. (2001). Avian collisions with wind turbines: a summary of existing studies and comparisons to other sources of avian collision mortality in the United States (No. 1E). RESOLVE, Inc.(US).

Ferrer, M., De la Riva, M., & J. Castroviejo (1991). Electrocution of raptors on power lines in southwestern Spain. Journal of Field Ornithology 62(2): 181-190.

Janss, G & Ferrer M (1999). Birds and power lines. Edt Quercus, Madrid.

Marques, A.T., Batalha, H., Rodrigues, S., Costa, H., Pereira, M.J.R., Fonseca, C., Mascarenhas, & Bernardino, J. (2014) Understanding bird collisions at wind farms: An updated review on the causes and possible mitigation strategies. Biological Conservation, 179, 40–52.

Masden, E.A., Haydon, D.T., Fox, A.D., Furness, R.W., Bullman, R. & Desholm, M. (2009) Barriers to movement: Impacts of wind farms on migrating birds. ICES Journal of Marine Science, 66, 746–753

Plonczkier, P. & Simms, I.C. (2012) Radar monitoring of migrating pink-footed geese: behavioural responses to offshore wind farm development. Journal of Applied Ecology, 49, 1187–1194

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