Abstract :
Many large terrestrial and wetland birds and some smaller, fast-flying species are prone to colliding
with overhead wires associated with power infrastructure. A high proportion of these are threatened
species and for some, collision with power lines and other man-made structures is a significant and
damaging source of anthropogenic mortality. We review the existing literature on the nature, scale
and impact of this problem worldwide, with particular emphasis on the South African situation, and
focus on the evidence for and against various line configurations and devices proposed tomitigate the
negative effects of overhead lines on bird populations. Cranes, bustards, flamingos, waterfowl,
shorebirds, gamebirds and falcons are among themost frequently affected avian groups, and collision
frequency is thought to be an influential factor in ongoing population declines in several species of
cranes, bustards and diurnal raptors. The bulk of the research on this issue has been done in North
America, Scandinavia, southern Europe and South Africa. Few comprehensive experimental studies
on ways to reduce avian collisions with power lines have been carried out, although most of these
have yielded quite clear results. Mitigation options considered include reviewing the placement of
proposed new lines, removing the earth-wire which is usually the highest, thinnest and most
problematic component in an overhead power line configuration, or else fitting this wire with
markers – brightly coloured ‘aviation’ balls, thickened wire coils, luminescent, shiny or hinged
flashing or flapping devices. All of these options reduce bird collision frequency overall by at least
50–60%, although the efficacy of linemarkingmay bemuch lower for certain species (e.g. bustards).
There remains considerable uncertainty about the best-performing marking device (perhaps because
performance may vary with both local conditions and the species involved in each instance), and
a durable, all-purpose device, that is effective both during the day and at night, has not yet been
developed.We conclude by outlining a proposed experimental evaluation of the full array of collision
mitigation options, to select the best approaches for use under South African conditions.
