The Research Institute for Nature and Forest currently performs a long-term project to study the impact of land-based wind turbines on birds (nature) and to act as a consultancy for proposed wind farms in Flanders. The project started in 2000, under the authority of the Flemish government. Preliminary study results of the monitoring were presented in Everaert et al. (2002), Everaert (2003), Everaert & Stienen (2006) and Everaert (2006 a, b). A ‘Bird 2 Atlas’ with important bird areas and migration routes in Flanders was also made available (Everaert et al. 2003). In 2007, a comprehensive report will be published with the monitoring results from 2002-2006 and further recommendations (Everaert 2007). A new article for a scientific journal will follow. Also advice on the establishment of off-shore windfarms has been prepared.

Discussion

Research results of individual wind farms can not be generalised. In general, the collision mortality is mostly related to the number of (flying) birds present (at rotor height). Large modern turbines of 1500 kW or more can have as much or even more collision fatalities than smaller turbines. However, more data on large wind turbines (>= 1500 kW) are urgently needed.

The average number of collision fatalities in different European wind farms on land varies between a few birds up to 64 birds per turbine per year. Also within one wind farm, the impact can strongly differ between individual turbines (Everaert et al. 2002; Everaert & Stienen 2006), clearly showing that ‘site selection’ can play an important role in limiting the number of collision fatalities. During previous years, for a few wind turbines at the eastern port breakwater in Zeebrugge, up to 111 and 125 fatalities were calculated as a result of the correction factors for some small birds that were occasionally found (Everaert et al. 2002; Everaert 2003). In Sylt and Helgoland, Germany (each with only one wind turbine), after a full year study, bird deaths per turbine per year were estimated to be respectively 2.8-103 and 8.5-309 (Benner et al. 1993). One example of multiple bird kills occurred at a wind turbine in Nasudden, Sweden, where 49 collided birds were found after one night with poor weather conditions; the turbine was not operational at the time, but was lit with a single lamp 10 m above the ground (Gill et al. 1996; Karlsson 1983). Overall, mortality events of this magnitude are rarely recorded, but with more and bigger wind turbines planned (certainly offshore), it is still unclear if this will stay a relatively rare phenomenon. More intensive searches during the whole year and with many wind turbines at different types of locations are urgently needed.

Towards the situation for migrating birds, Kaatz (2002) recommended not to build large wind turbines on the coast, because of disturbance (barrier) at dense migration corridors. Here it is difficult to prove the evidence of the large numbers of victims of which the biggest part are the small birds. Many small corpses are lost after collision with the rotors, whereby they can’t be found on the ground or are lost into sea. Even for large wind turbines the speed of the rotors goes to about 230 km/h at the tips. Therefore, the estimated collision of small birds using searches of dead birds on the ground (as with most studies) is not fully reliable, even with corrections for scavenging and search efficiency. The only – known to us – comprehensive study whereby the collision chance for nocturnal migrating birds was calculated by means of the actual observed collisions (thermal image intensifiers) was performed in The Netherlands (Winkelman 1992b). These results showed a remarkable high nocturnal collision probability of 1 on 40 passing birds (2.5%) at rotor height.

 

General recommendations

Study results clearly show that reasonable amounts of birds and bats can collide with wind turbines. An exhaustive study before the selection of future locations is a key factor to avoid deleterious impacts of wind farms on birds and bats.

Cumulative negative impacts with an increasing amount of wind turbines must be taken into account (Langston & Pullan 2003). This especially is developing along fixed bird migration corridors (coasts, mountain passes). More wind farms also means an extra pressure on top of the already existing sources of negative impact (powerlines, traffic etc.). In a densely populated region like Flanders, this degrades the total suitability for ecological functions such as the presence of bird and bat populations and the guarantee for regional or international migration routes. For the offshore situation, international cooperation will be necessary to determine the possible cumulative impact.

Proper site selection plays a very important role in limiting the impact of wind farms on nature. In general, current knowledge indicates that there should be precautionary avoidance of locating wind farms in regional or international important bird or bat areas and/or migration routes. Locations with high bird or bat use are not suitable for wind farms.

Developing mitigation measures and advocating temporary shutdowns or a complete dismantling of wind farms where (probable) significant impacts occur, are very difficult and sensitive issues and could take years of study. Such situations must be prevented. A number of environmental impact assessments (EIA) have important shortcomings because of the lack of data and time or the use of incomplete data (e.g. not covering the annual cycle). It is very important that EIA's are made independently or are at least evaluated independently. When important factors remain unclear and an indication exists for an important negative impact, the precautionary principle must be applied. A constructive working method is to map potential and no-go locations for wind energy in a certain country or region, based on all available information, long before concrete projects are planned.

Following the article 6(4) of the European Habitats Directive, it is clear that if a wind farm could have an important negative impact on wildlife, landscape, etc., the obligation exists to look for alternatives first. In most cases there will always be less vulnerable locations or other alternatives for wind farms. To evaluate location or other alternatives, a multicriteria analysis (MCA) is preferable. This complex decision-making tool resembles (strategic) costbenefit analysis although it does not reduce the disparate phenomena to a common unitary (monetary) base. It permits the inclusion of qualitative as well as quantitative data.

Several environmental impacts (positive or negative) cannot be readily assigned a monetary value (for example collision mortality and disturbance for wildlife (birds/bats), impact on landscape, etc.). The current lack of sufficient knowledge concerning positive and negative effects of wind energy, however, remains a problem for the implementation of such analysis.

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