A study of large terrestrial bird powerline collisions in the Karoo
Mark D. Anderson
Various threatened and endemic large terrestrial birds occur in the Karoo. Due to extensive farm management practices in this area, these birds face few unnatural threats. However, it has been suggested that many birds are killed annually when they collide with the earth-wires of powerlines. This impact is probably the single most important threat to large terrestrial birds in the Karoo. For this reason a study to investigate this problem and to propose solutions to Eskom was considered an urgent priority.
This study takes place in the eastern Karoo, in the Platberg-Karoo Conservancy and surrounding area. The eastern Karoo supports large populations of large terrestrial birds, including 25% of the world Blue Crane population. The Platberg-Karoo Conservancy is an Important Bird Area as it supports large numbers of threatened and endemic bird species.
The aim of this study is to investigate bird collisions with powerlines of different configurations. Two 10 km transects have been selected along powerlines of the various configurations and voltage levels (11 - 400 kV; 12 transects in total). The transects were selected to include different habitat types, topography, line direction, etc.
These transects are searched for dead birds on a bi-monthly basis by motor-cycle, driving in a zig-zag pattern. When a carcass is located various information about the bird and terrain is collected. In this way it is anticipated that information will be obtained about the characteristics of the sites where collisions take place, thus allowing extrapolation to other areas. This will also allow for a pro-active approach to the fitting of mitigation devices to powerlines.
Another aspect of the study is to determine the effectiveness of the mitigation devices. This involves monitoring sections of lines, (where the earth-wires have been fitted with bird flight divertors [spirals/pigtails] and bird flappers), using the methodology given above. Here a 22 kV, 132 kV and 400 kV that have been fitted with spirals are monitored. Also an experiment is being conducted along a 400 kV powerline (near De Bad, just south of De Aar) to test the effectiveness of spirals vs bird flappers (spaced at two different intervals). The latter powerline was selected because it is near two dams, where a large number of Blue Cranes roost (up to 850 individuals at Kafferspoortdam). Large numbers of large terrestrial bird carcasses have been found below this powerline.
The main objectives of the study are:To identify parameters which influence large terrestrial bird collisions by studying, inter alia, the terrain where strikes occur.
To identify specific areas where collisions are likely to occur.
To provide recommendations to Eskom about the biological significance of these impacts.
To propose solutions to the collision problem and to monitor the effectiveness of mitigation devices that have been fitted to specified collision “hot spots”.