1. Wind power plants represent a risk of bird mortality, but the effects are still poorly quantified. We measured bird mortality, analysed the factors that led birds to fly close to turbines, and proposed mitigation measures at two wind farms installed in the Straits of Gibraltar, one of the most important migration bottlenecks between Europe and Africa.

2. Bird corpses were surveyed along turbine lines and an associated power line to estimate mortality rates. The behaviour of birds observed within 250 m of turbines was also recorded as a putative indicator of risk. The effects of location, weather and flight behaviour on risk situations (passes within 5 m of turbines) were analysed using generalized linear modelling (GLM).

3. Mortality caused by turbines was higher than that caused by the power line. Losses involved mainly resident species, mostly griffon vultures Gyps fulvus (0·15 individuals turbine ? 1 year ? 1 ) and common kestrels Falco tinnunculus (0·19 individuals turbine ? 1 year ? 1 ). Mortalities were not associated with either structural attributes of wind farms or visibility.

4. Vulture collisions occurred in autumn–winter and were aggregated at two turbine lines where risks of collisions were greatest. The absence of thermals in winter forced vultures to use slopes for lift, the most likely mechanism influencing both their exposure to turbines and mortality.

5. Kestrel deaths occurred during the annual peak of abundance in summer. Carcasses were concentrated in the open habitats around a single wind farm and risk may have resulted from hunting habitat preferences.

6. Synthesis and applications . We conclude that bird vulnerability and mortality at wind power facilities reflect a combination of site-specific (wind–relief interaction), speciesspecific and seasonal factors. Despite the large number of migrating birds in the study area, most follow routes that are displaced from the facilities. Consequently, only a small fraction of birds on migratory flights was actually exposed to turbines. New wind installations must be preceded by detailed behavioural observation of soaring birds as well as careful mapping of migration routes.

Luis Barrios
SEO/BirdLife, Madrid, Spain

Alejandro Rodríguez
Department of Applied Biology, Estación Biológica de Doñana CSIC, Seville, Spain

Journal of Applied Ecology (2004) 41, 72–81

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Does large-scale development of industrial wind energy actually reduce the consumption of fossil fuels or emission of CO₂?

Comparison of per-capita wind and thermal electricity production and CO₂ emissions in Germany, Denmark, Spain, and France.

Germany — most industrial wind facilities in the world (18,400 MW in 2005) –
2005: 10.6 tonnes CO₂ per capita, 6.4 tonnes from electricity
+190% per capita production from wind from 2000 to 2005
+9% per capita thermal electricity production from 2000 to 2005
+1% per capita CO₂ from electricity 2000 to 2005

Denmark — highest percentage of industrial wind in the world (18% of production) –
2005: 9.3 tonnes CO₂ per capita, 5.5 tonnes from electricity
+54% per capita production from wind from 2000 to 2005
−8% per capita thermal electricity production from 2000 to 2005
−11% per capita CO₂ from electricity 2000 to 2005

Spain — second most industrial wind facilities in the world (10,000 MW in 2005) –
2005: 8.5 tonnes CO₂ per capita, 3.8 tonnes from electricity
+317% per capita production from wind from 2000 to 2005
+41% per capita thermal electricity production from 2000 to 2005
+10% per capita CO₂ from electricity 2000 to 2005

France — virtually no industrial wind (760 MW in 2005) –
2005: 6.6 tonnes CO₂ per capita, 2.6 tonnes from electricity
+~0% per capita production from wind from 2000 to 2005
+19% per capita thermal electricity production from 2000 to 2005
−1% per capita CO₂ from electricity 2000 to 2005

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