2012

High- and very-high-voltage power lines have been identified as a major human-induced source of mortality for birds. When birds fly in large groups, or in poor visibility conditions, they can collide with these structures, in some instances in sufficiently large numbers to raise concern. Several international agreements on nature conservation acknowledge this important issue. In answer to this concern, Elia, as the power transmission system operator in Belgium, intends to identify its own overhead power lines that present a serious collision risk for birds.

The main objective of this project is to map collision-prone power lines in Belgium and to classify existing power lines according to their "dangerousness" in this regard. This report's priority classification of power lines should ultimately be seen as an answer to the following question: "Given present-day knowledge of bird distribution and relative sensitivity to collision mortality, what are the most dangerous power-line sections, i.e. those where the mitigation of collision risk should be focused as a priority?" It is neither a substitute for a proper Environmental Impact Assessment nor a mitigation plan in itself.

As a first step, a list of collision-sensitive bird species in Belgium was compiled on the basis of a review of the literature, casualty records and expert judgment. Not only "collision risk" itself was taken into account, but also the "conservation value" of each species and the probable population impact of additional mortality.

In a second step, this list was used to define four coherent bird species groups of interest, in order to facilitate and organize the mapping work. These groups are the waterbirds (for which numerous data are available at site level), rare breeding birds (for which good data are also available in both Wallonia and Flanders), which migrate in large numbers (the mapping exercise was more difficult for them, because migration is to a considerable extent geographically spread across Belgium, with no clear migrant funnel) and widespread breeding bird species (for which relative density maps need to be built because they are not associated with specific sites or locations).

In a third step, up-to-date knowledge of bird distribution in Belgium was used to create maps for each of the coherent bird species groups. Numerous sources of data were used: wintering waterbird counts, roost and colony counts, breeding bird atlases and observations from data- recording portals. Spatial modelling was applied to obtain high-resolution maps of widespread species and help define the best staging area for some other species.

A "collision risk score" was defined for each of the geographical zones delimited on the maps, or based on the distance from important bird areas. The combination of the maps, with the aid of this scoring system, allows the classification of all power-line masts according to their associated collision risk for birds.

Most of the more dangerous power lines are located in areas with major concentrations of waterbirds occur: the polders area, the wetlands in the vicinity of the Port of Antwerp and some river valleys (Yser, Meuse, Haine). About 3.4% of the network can be considered "high priority" for mitigation.

A technical chapter describes the available mitigation tools. In the case of existing power lines, a cost-effective manner to decrease collision risk involves placing markers or "diverters" on the lines, in order to make them more visible to birds, even in poor visibility conditions. On the basis of current knowledge, it can be concluded that any large device (increasing the apparent size of the line to at least 20 cm), placed at least every 5-10 m along the line, preferably on the earth wire, is likely to significantly reduce collision risks.

In view of the available budget, the placement of diverters can now be planned on Belgian power lines, focusing first on the high priority sections. Of course, other considerations, such as geographical "grouping" of diverters in order to reduce cost and opportunities provided by other planned work on specific power-line sections, may also influence the final planning, which is now in Elia's hands.