Electric fence induced mortality in South Africa
Recent advances in electronic technology have ensured that electric fences offer a viable means of reducing the chances of wildlife escaping from conservation areas and private game ranches. Electric fencing is even gaining popularity amongst domestic stock farmers in controlling the movement of problem animals into private land. However, there is a growing concern over the number of electric fence induced mortalities in South Africa. This research project sampled mortality rates in a number of broadly distributed study areas with the aim of determining (1) which species were prone to being electrocuted, (2) the average number of mortalities km-1, and (3) which aspects of electric fence design contribute to most to the observed number of mortalities. This information would then be used in proposing a variety of means of amelioration. Individuals from 33 species were documented as being killed as a direct result of electric fencing infrastructure. Leopard Tortoises (Stigmochelys pardalis), Rock Monitors (Varanus albigularis), Southern African Python (Python natalensis), Pangolin (Manis temminckii), Lobatse Hinged Tortoise (Kinexys lobatsiana) and Porcupine (Hystrix africaeaustralis) emerged to be the species killed most frequently by electric fences. Annual mortality rates for reptiles ranged between 0 and 2.15 individuals.km-1.yr-1 ( = 0.475 individuals.km-1.yr-1) with the highest mortality rates occurring areas using low-level tripwires erected below 200 mm. The influence of strand height on mortality rate per km-1 was confirmed by the fact that average mortality rates showed a marked decrease in areas where the lowest electrified strand was erected at a height of 200 mm and greater. Possible means of amelioration include raising the height of the bottom electrified strand to a height of no less than 200 mm, increasing the distance that this lowest electrified strand is offset from the main fence, erecting some form of barrier wall, using rock packed aprons instead of low-level tripwires, and, where feasible, using duty cycle switches to switch the fences on at dusk and off at dawn.