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.

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Abstract: We studied the impact of a wind farm (line of 25 small to medium sized turbines) on birds at the eastern port breakwater in Zeebrugge, Belgium, with special attention to the nearby breeding colony of Common Tern Sterna hirundo, Sandwich Tern Sterna sandvicensis and Little Tern Sterna albifrons. With the data of found collision fatalities under the wind turbines, and the correction factors for available search area, search efficiency and scavenging, we calculated that during the breeding seasons in 2004 and 2005, about 168 resp. 161 terns collided with the wind turbines located on the eastern port breakwater close to the breeding colony, mainly Common Terns and Sandwich Terns. The mean number of terns killed in 2004 and 2005 was 6.7 per turbine per year for the whole wind farm, and 11.2 resp. 10.8 per turbine per year for the line of 14 turbines on the sea-directed breakwater close to the breeding colony. The mean number of collision fatalities when including other species (mainly gulls) in 2004 and 2005 was 20.9 resp. 19.1 per turbine per year for the whole wind farm and 34.3 resp. 27.6 per turbine per year for 14 turbines on the sea-directed breakwater. The collision probability for Common Terns crossing the line of wind turbines amounted 0.110-0.118% for flights at rotor height and 0.007-0.030% for all flights. For Sandwich Tern this probability was 0.046-0.088% for flights at rotor height and 0.005-0.006% for all flights. The breeding terns were almost not disturbed by the wind turbines, but the relative large number of tern fatalities was determined as a significant negative impact on the breeding colony at the eastern port breakwater (additional mortality of 3.0-4.4% for Common Tern, 1.8-6.7% for Little Tern and 0.6-0.7% for Sandwich Tern). We recommend that there should be precautionary avoidance of constructing wind turbines close to any important breeding colony of terns or gulls, nor should artificial breeding sites be constructed near wind turbines, especially not within the frequent foraging flight paths.

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