Staggered towers on parallel transmission lines: a new mitigation measure to reduce collisions of birds, especially bustards
Keywords:bird mortalities, Namibia, power lines, span position, South Africa
Significant numbers of birds are killed annually by flying into power lines across Africa, and numerous attempts have been made to mark lines to make them more conspicuous, to reduce these collisions. Results from surveys reported in this paper and many others indicate that bustards (family Otidae) are most susceptible. Bustard fatalities are not greatly reduced by adding bird diverters to earth wires. Here we propose a new mitigation measure that may reduce the number of mortalities by two-thirds where two power lines run in parallel: staggered towers. Power line surveys in Namibia and South Africa indicate that 87% of 134 bird collisions occurred in and near the middle sections of a span, while only 13% of collisions occurred near the towers themselves. Despite the skull morphology of bustards creating a blind spot immediately ahead of them, it appears that the towers are big enough to be seen (or heard) and avoided. Thus, by aligning power lines of similar size in parallel and as close as technically feasible and staggering the towers such that each tower is aligned with the mid-span of the neighbouring line, the lines may become more visible. This should allow collision-prone birds to gain altitude and fly over the lines. Theoretically, this method is expected to reduce power line fatalities by 67% for each new line. We call for experimental validation of this novel mitigation measure.
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