Remove earth wires to reduce incidental bird mortality

Overall effectiveness category Likely to be beneficial
Number of studies: 2
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How is the evidence assessed?

Effectiveness

90%
Certainty

60%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

Earth wires act to protect transmission wires against lightning, by dispersing excessive electricity. They are normally positioned either above or below the transmission wires, increasing the vertical height of wires and therefore the chances of collisions. In addition, earth wires tend to be thinner than transmission wires and so less visible, which, when they are positioned above transmission wires, increases the chances of collisions as birds climb to avoid the transmission wires.

Study locations

Key messages

A before-and-after study and a literature review describe significant reductions in collision mortalities of cranes Grus spp. and grouse Lagopus spp. following the removal of earth wires.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A controlled before-and-after trial between 1989 and 1995 in boreal and subalpine forests in southern Norway (Bevanger & Broseth 2001) found a 51% decrease in collision mortality of willow grouse Lagopus lagopus and rock ptarmigan L. mutus by a 2.5 km section of 22 kV power line from which the earth wire was removed (49 fatalities before removal, 24 afterwards). There was no corresponding decrease in two control sections (61 vs. 50 fatalities and 20 vs. 27 fatalities). The earth wire was located 1.5 m below the phase conductor lines.
Study and other actions tested
Referenced paper
Bevanger K. & Brøseth H. (2001) Bird collisions with power lines – an experiment with ptarmigan (Lagopus spp.). Biological Conservation, 99, 341-346.
A literature review (Jenkins et al. 2010) described a before-and-after trial (Brown et al. 1987) that found an 80% reduction in collision mortality of sandhill cranes Grus canadensis and whooping cranes G. americana following removal of the earth wire from a 3.2 km span of 116 kV line in Colorado, USA.
Additional reference
Brown, W. M., Drewien, R. C. & Bizeau, E. G. (1987) Mortality of cranes and waterfowl from powerline collisions in the San Luis Valley, Colorado. 128–136 Proceedings of the crane workshop, 1985 Platte River Whooping Crane Maintenance Trust, Grand Island, Nebraska.
Study and other actions tested
Referenced paper
Jenkins A., Smallie J. & Diamond M. (2010) Avian collisions with power lines: a global review of causes and mitigation with a South African perspective. Bird Conservation International, 20, 263-278.

Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2020) Bird Conservation. Pages 137-281 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Bird Conservation

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