Wind power is likely to play an increasingly role in generating renewable energy throughout Europe. More and more wind farms are being built, and others are planned in the next few years. What could their impact on migrating birds eventually be? Researchers are turning to such issues and questions. A first answer is now coming from Denmark.
Migrating birds are thought to be vulnerable to collisions with the wind turbines. A recent Danish study has designed a risk management tool to identify the most vulnerable bird species and help assessing the impact of offshore wind farms on all species of migrating birds. A difficult task, indeed, and a very costly one: the radar technology needed for visual and aerial surveys can are not cheap at all. This study, ( Desholm, M. (2009). Avian sensitivity to mortality: Prioritising migratory bird species for assessment at proposed wind farms. Journal of Environmental Management. 90: 2672-2679) has developed a simple and cost-effective method to assess which species are most at risk from collisions.
Two indicators are used in the framework: the relative abundance of breeding populations of birds potentially affected by a wind farm and the vulnerability of a species to death from collisions with wind turbines. Combining both these indicators into one index (‘Environmental Sensitivity Index’) allows the risk to different species to be classified as low, medium or high priority.
The conservation status of different species should be used in conjunction with this index, particularly if a species’ status is near the borderline of different priority status thresholds.
A case study, demonstrating the use of the framework, was based on the large Nysted wind-farm off the coast of Denmark. The area is considered to be a migration hotspot, with thousands of geese and ducks and substantial numbers of migrating birds of prey and passerines (mostly land birds) passing through the area during the autumn migration.
Of the 38 species under investigation, birds of prey and waterbird populations were most at risk of suffering as a result of collisions with the wind turbines. These species tend to be long-lived, mature late and lay few eggs, all of which affect the adult survival rate, and consequently the growth of a population. These two groups represented 53 per cent of all the species in the study. Another 34 per cent of the species were at medium risk. Only passerines showed a low risk from wind farms.
For individual species of birds, the tundra swan and barnacle goose were found to be the most at risk from the windfarm. The hirudines (swallow and martin family) and Eurasian siskin were the least at risk. The 15 most abundant species flying past the windfarm were all birds of prey, waterbirds and hirudines.
The framework can be used:
* by planners who need to identify which bird species need further impact studies
* to assess the cumulative effects of multiple wind farms
* to help decision makers make better use of limited resources when planning wind farms developments by understanding which bird species are most at risk
* for the assessment of bird collisions with other obstacles, such as tall buildings, power lines, telecommunication towers and aircraft
New knowledge should be integrated into the framework, as it becomes available. For example, new research showing that night flying species tend to fly at higher altitudes than previously thought was integrated into the framework. This showed that these species were not in fact at greater risk of colliding with wind turbines.