Background
With respect to negative effects of wind farms, the authors write that "the displacement of birds away from turbines can result in individuals abandoning otherwise suitable habitat," and they say that such "has been found to occur in a number of individual wind farm studies," citing the works of Leddy et al. (1999), Larsen and Madsen (2000), Kowallik and Borbach-Jaene (2001), Hotker (2006), Hotker et al. (2006) and Larsen and Guillemette (2007). In fact, they report that "some poorly sited wind farms have resulted in sufficient deaths to produce a population-level effect," referencing the studies of Barrios and Rodriguez (2004, 2007), Everaert and Stienen (2006), Smallwood and Thelander (2007), Sterner et al. (2007) and Thelander and Smallwood (2007).

What was done
In an effort designed to study this issue more broadly, Pearce-Higgins et al. assessed the degree of occurrence of twelve widely-distributed species of breeding birds within the vicinity of wind farm infrastructure (turbines, access tracks and overhead transmission lines) on twelve different wind farms located within unenclosed upland habitats (moorland, rough grassland and blanket bog) in the United Kingdom, which sites included most of the existing large upland wind farms in Scotland and northern England.

What was learned
The five UK scientists obtained "considerable evidence for localized reduction in breeding bird density on upland wind farms." More specifically, they report that after accounting for habitat variation, "seven of the twelve species studied exhibited significantly lower frequencies of occurrence close to the turbines," and that there was "equivocal evidence of turbine avoidance in a further two," while "no species were more likely to occur close to the turbines." Access tracks, on the other hand, proved much less of a nuisance than turbines; and there was no evidence for consistent avoidance of overhead transmission lines. All things considered, they thus concluded that "levels of turbine avoidance suggest breeding bird densities may be reduced within a 500-m buffer of the turbines by 15-52%, with buzzard (Buteo buteo), hen harrier (Circus cyaneus), golden plover (Pluvialis apricaria), snipe (Gallinago gallinago), curlew (Numenius arquata) and wheatear (Oenanthe oenanthe) most affected."

What it means
Pearce-Higgins et al. say their findings emphasize the need for a "strategic approach" to ensure that wind farm development avoids areas with high densities of potentially vulnerable species, not only in the UK, but "across other similar windy semi-natural habitats in northwest Europe, southern South America, and central North America," where efforts should be made to "avoid high densities of potentially vulnerable open country species such as waders and raptors." Their findings thus augment those of many others who have also raised serious questions about the constructing of wind farms in inappropriate locations, while indicating just how difficult it may be to avoid such sites.

References
Barrios, L. and Rodriguez, A. 2004. Behavioral and environmental correlates of soaring bird mortality at on-shore wind turbines. Journal of Applied Ecology 41: 72-81.

Barrios, L. and Rodriguez, A. 2007. Spatiotemporal patterns of bird mortality at two wind farms of Southern Spain. In: De Lucas, M., Janss, G.F.E. and Ferrer, M. (Eds.), Birds and Wind Farms. Quercus, Madrid, Spain, pp. 56-72.

Everaert, J. and Stienen, E.W.M. 2006. Impact of wind turbines on birds in Zeebrugge (Belgium). Significant effect on breeding tern colony due to collisions. Biodiversity and Conservation 16: 3345-3359.

Hotker, H. 2006. The Impact of Repowering of Wind Farms on Birds and Bats. Michael-Otto-Institut im NABU, Bergenhusen.

Hotker, H., Thomsen, K.-M. and Jeromin, H. 2006. Impacts on Biodiversity of Exploitation of Renewable Energy Sources: The Example of Birds and Bats -- Facts, Gaps in Knowledge, Demands for Further Research and Ornithological Guidelines for the Development of Renewable Energy Exploitation. Michael-Otto-Institut im NABU, Bergenhusen.

Kowallik, C. and Borbach-Jaene, J. 2001. Impact of wind turbines on field utilization by geese in coastal areas in NW Germany. Vogelkundliche Berichte aus Niedersachen 33: 97-102.

Larsen, J.K. and Guillemette, M. 2007. Effects of wind turbines on flight behavior of wintering common eiders: Implications for habitat use and collision risk. Journal of Applied Ecology 44: 516-522.

Larsen, J.K. and Madsen, J. 2000. Effects of wind turbines and other physical elements on field utilization by pink-footed geese (Anser brachyrhynchus): a landscape perspective. Landscape Ecology 15: 755-764.

Leddy, K.L., Higgins, K.F. and Naugle, D.E. 1999. Effects of wind turbines on upland nesting birds in conservation reserve program grasslands. Wilson Bulletin 111: 100-104.

Smallwood, K.S. and Thelander, C. 2007. Bird mortality in the Altamont pass wind resource area, California. Journal of Wildlife Management 72: 215-223.

Sterner D., Orloff, S. and Spiegel, L. 2007. Wind turbine collision research in the United States. In: De Lucas, M., Janss, G.F.E. and Ferrer, M. (Eds.). Birds and Wind Farms. Quercus, Madrid, Spain, pp. 81-100.

Thelander, C.G. and Smallwood, K.S. 2007. The Altamont pass wind resource area's effect on birds: a case history. In: De Lucas, M., Janss, G.F.E. and Ferrer, M. (Eds.). Birds and Wind Farms. Quercus, Madrid, Spain, pp. 25-46.