Wind turbines can have a negative impact on birds and bats. Several field studies have shown that birds and bats can collide with the turbines during local flights and seasonal migration, or they can become disturbed in their breeding, resting and foraging areas or during migration (Langston and Pullan 2003; Kingsley and Whittam 2005).
The government of Flanders (northern part of Belgium) has the ambition to reach 6% of the electricity supply from renewable sources like wind energy by 2010. Many wind farms are planned in the near future. In September 2000, the circular letter EME/2000.01 of the Flemish government was produced, outlining the criteria and pre-conditions for the construction of wind farms. Based on the circular letter, a "wind plan" was established for the Flemish part of Belgium (VUB & ODE Vlaanderen 2001). This wind plan can produce useful information on spatial and wind-technical feasibility of specific projects. Additionally, a bird atlas (see further) can also be used to evaluate the proposed or potential wind farm areas in relation to nature values (Everaert et al. 2003). In 2006, a new circular letter EME/2006/01 was made which replaced the older version (Vlaamse regering 2006). The authorities have the obligation by official order to strictly apply the current circular letter.