Reducing bird mortality caused by high- and very-highvoltage power lines in Belgium

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 datarecording
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.