Action: Install electric fencing to protect crops from mammals to reduce human-wildlife conflict
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- Eleven studies evaluated the effects of installing electric fencing to protect crops from mammals to reduce human-wildlife conflict. Three studies were in Japan, three were in the USA, two were in the UK and one each was in Namibia, India and Guinea-Bissau.
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OTHER (11 studies)
- Human-wildlife conflict (11 studies): Nine of 11 studies (including three before-and-after studies and three controlled studies), in the USA, the UK, Japan, Namibia, India and Guinea-Bissau, found that electric fences deterred crossings by mammals, ranging in size from European rabbits to elephants. Two studies had mixed results, with some fence designs deterring elephants and black bears.
Wild mammals can compete with domestic herbivores for food, can predate domestic herbivores or can damage crops. Human-wildlife conflict can be reduced if wild mammals can be effectively excluded from fields. Electric fences are extensively used and can reduce the risk of wild mammal incursions into such fields. If successful, they may reduce incentives for carrying out lethal control of such mammals.
Supporting evidence from individual studies
A before-and-after study in 1961–1965 in a forest in New York State, USA (Tierson 1969) found that an electric fence reduced browsing on hardwood trees by white-tailed deer Odocodus virginusnus. Three years after fence erection, there were more unbrowsed stems inside the fence (43 unbrowsed stem/plot) than outside (16 unbrowsed stems/plot). There had been no difference in browsing rates before fence erection (inside fence line: 22 unbrowsed stems/plot; outside fence line: 22 unbrowsed stems/plot). The fence (2.5 miles perimeter) consisted of five wires, with the lower three electrified from November 1961. Browsing intensity was measured in plots measuring one rod-square (approximately 25 m2). Twenty plots inside and 20 outside the fence were surveyed in 1961 and 1964.
A replicated, before-and-after, site comparison study in 1980–1983 on 24 arable sites in southern UK (McKillop & Wilson 1987) found that electric fences reduced European rabbit Oryctolagus cuniculus numbers on crops. Rabbit numbers fell on plots protected by a Flexinet® fence (0–4 weeks after erection: 6.7 rabbits/count; 5–20 weeks after erection: 7.6 rabbits/count; before erection: 42.7 rabbits/count) and a Livestok® fence (0–4 weeks after erection: 10.1 rabbits/count; 5–20 weeks after erection: 17.6 rabbits/count; before erection: 48.0 rabbits/count). Rabbit numbers in unfenced plots remained constant throughout (0–4 weeks after erection: 15.9 rabbits/count; 5–20 weeks after erection: 13.3 rabbits/count; before erection: 13.6 rabbits/count). Electric fences (0.5 m high) were erected along one side of winter barley fields. Flexinet® (seven sites) had 80 × 80-mm mesh and Livestok® (seven sites) had 500 × 50-mm mesh. Ten unfenced sites were also monitored. Adult rabbits were counted using spotlights and binoculars in November–April between 1980 and 1983.
A controlled study in 1988–1989 on an arable farm in Devon, UK (Wilson 1993) found that electric fencing reduced damage to an oat Avena sativa crop by badgers Meles meles in one of two years. Results were not tested for statistical significance. In the first year, 1.8–2.6% of crop area in fields protected by electric fencing was damaged by badgers, compared to 9.6% in an unfenced field. In the second year, 2.2–4.3% of fenced crop was damaged compared to 1% of unfenced crop. Electric fences around two fields had parallel wires at 10 cm and 20 cm above the ground. Wires were connected to a fence energiser, powered from a 12-volt battery. A third field was unfenced. Vegetation short circuited the fence, especially in 1988. In 1989, dry conditions may have reduced soil conductivity, thus reducing fence voltage. Damage (mostly flattened stalks) was assessed by walking crops in August 1988 and 1989. Additionally, 1988 data were verified using aerial photographs.
A replicated study in 1997–1998 of 24 crop fields and two areas of beehives adjacent to woodlands in Nagano prefecture, Japan (Huygens & Hayashi 1999) found that electric fences prevented raids by Asiatic black bears Ursus thibetanus. No bears got through any of the electric fences. Bear activity near fences was documented 23 times, including three bears departing after touching the fence, one trying unsuccessfully to dig under the fence and eight raids on unprotected fields within 13–120 m of fences. In July–October of 1997 and 1998, twenty-four sweetcorn fields and two areas of beehives (area enclosed 0.001–0.75 ha) with recent history of bear-raids were fenced using Gallagher power fence systems for 2–65 nights/fence. Fences comprised four wires at 24 cm intervals with a further wire 30 cm outside the fence and 30 cm above the ground.
A replicated, before-and-after study in 1991–1995 on farmland and grassland at four sites in East Caprivi, Namibia (O'Connell-Rodwell et al. 2000) found that some electric fences reduced crop losses to elephants Loxodonta africana. At one village, where 31 farms were enclosed within a 9.5-km-long permanent electric fence, there were no compensation claims for losses to elephants over two years following installation, compared to 30 claims over the previous three years. A 4-km-long permanent electric fence at another site was unsuccessful, due to inadequate installation or maintenance. At a third site, temporary electric fences kept out elephants at one village in one year. In the second year, the fence was effective but elephants were able to walk around the side. At a fourth temporary fence site, no elephants returned after electric fence installation, so its effectiveness was untested. The two, 2 m-high, permanent steel wire electric fences comprised two strands of 2-mm steel wire attached to trees or poles. The temporary fences (<2 km long) at two villages comprised polyurethane cords, threaded with wire strands, strung between trees. Fences were powered by 12-volt batteries. Data were collated from questionnaire surveys in 1991–1995.
A randomized, replicated, controlled study in 2002–2004 at a woodland and grassland site in Ohio, USA (Seamans & VerCauteren 2006) found that electric fencing deterred white-tailed deer Odocoileus virginianus when turned on. Significantly fewer deer entered enclosures with electric fencing (0–1 deer/day) than entered enclosures without fencing (72–86 deer/day). When power was applied to fencing in week two, deer entries decreased 88–99%. When power was delayed 10 weeks, entries decreased 90%. When power was turned on and off within a 4-week period, entries decreased 57%. Corn consumption was lower in powered (<2–6.4 kg/day) than in unpowered sites (15–32 kg/day). Ten sites (> 1 km apart) each had two 5 × 5 m enclosures (9 m apart), fenced on three sides, each containing a feed trough that measured food (corn) consumption. Infra-red cameras monitored enclosures. In February 2002, 1.3-m-high electric fencing (7 kV; ElectroBraid™) was installed around one enclosure in each pair. After one week, the treatment and control were swapped. In March 2002, one feed trough was removed from each pair, leaving five sites with troughs, surrounded by electric fencing and five unfenced troughs, for three weeks. In December 2002, all sites had electric fencing but five had it turned on and five off for one week. Power was then off for two weeks and then the same repeated. Treatment and control sites were then swapped (10 weeks since start) with the power on for three weeks at treatment sites. In January 2004, five were fenced and five were controls without fencing, for six weeks. Before each trial there was a week with no treatments.
A study in 2007–2008 of three fences in Japan (Honda et al. 2009) found that electric fencing was effective at excluding a range of large and medium-sized wild mammals. No mammals were recorded inside any fences. Outside the lowest fence, there were 157 occurrences of eight species. Outside the intermediate-height fence, there were 96 occurrences of eight species. Outside the highest fence, there were 117 occurrences of three species. Japanese macaques Macaca fuscata, which can climb non-electrified fences, were among animals excluded at the highest fence. Fences enclosed areas of 100–930 m2. They comprised metallic 15 × 29 mm mesh in 0.6-m-high × 1.8-m-wide sections. The lowest fence (0.6 m high) was a single section high. The intermediate fence (1.6 m high) comprised a single wire between two mesh sections. The highest fence (1.8 m high) comprised three wires and nylon netting between two mesh sections, with two ground wires above. A current (2,000–6,500 V) ran through metallic parts. A corrugated polyvinyl chloride sheet insulated the fence bottom from the ground.
A study in 2006–2009 in two areas of Assam, India (Davies et al. 2011) found that electric or chili fences reduced the probability of Asian elephants Elephas maximus damaging crops. The effectiveness specifically of electric fences was not analysed. The chance of crop damage occurring was lower when fences provided a barrier to crop-raiding elephants, compared to a range of other interventions or to no intervention (results presented as statistic model coefficients). However, loud noises alongside fences reduced their effectiveness. Within two study areas, 33 community members trained as monitors recorded 1,761 crop-raiding incidents, from 1 March 2006 to 28 February 2009. A range of deterrent methods, used singly or in combination, included two-strand electric fences, chili fencing (engine grease and ground chili paste, on a jute or coconut rope), chili smoke (from burning dried chilies, tobacco, and straw), spotlights, elephant drives (repelling wild elephants using domesticated elephants), fire and noise.
A replicated study in 2010 at four arable sites in Japan (Honda et al. 2011) found that a modified electric fence design was effective at excluding large and medium-sized mammals from crops. Fewer animals were recorded inside fences (0–3) than outside fences (60–327). Racoon dog Nyctereutes procyonoides (one occurrence), sika deer Cervus nippon (two) and wild boar Sus scrofa (one) crossed fences. The most frequently recorded mammals outside fences were wild boar (112 occurrences), sika deer (373) and Japanese macaque Macaca fuscata (117). Four fences enclosed cops covering 100–1,700 m2. They comprised insulated fiberglass poles (8.5 mm diameter, 2.1 m long) at 2.5-m intervals. Nine electrified wires (0.9 mm diameter) were attached, up to 1.7 m high. Nylon net (45-mm mesh) was attached to the full fence height. Poles were flexible, so animals attempting to climb would retain ground contact and hence be shocked. Measured voltages were 3,600–6,800 V. Fences were checked at least weekly. Animals were monitored inside and outside fences using infrared-triggered cameras for ≥5 months from April–November 2010.
A site comparison study in 2010 in a forested area in Michigan, USA (Otto & Roloff 2015) found that two of four electric fence designs successfully excluded black bears Ursus americanusi. Two of four electric fence designs excluded 100% of black bears from accessing bait within fenced enclosures during a total of 30–38 fence interactions. Bears breached the other two fence designs and accessed bait on three occasions during a total of 48–52 fence interactions. Each of four electric fence designs was tested at 2–3 baited sites within a 17-km2 forested area. The fences enclosed a 13-m2 area filled with 4–13 l of bait/day (including bread, cookies, trail mix, honey, bacon, sardines etc.). Fences were constructed with 2–3 rows of white polytape (1.3 cm) at different spacings (23–58 cm from the ground) and charged with 5,000 V (see original paper for details). Each site was baited for an average of three nights prior to fencing and was visited by bears during this time. Infrared cameras recorded bears interacting with the fences during 2–5 nights/site in June–August 2010.
A replicated, controlled study in 2008–2012 of 100 rice fields in the Bijagos archipelago and Oio and Gabau regions, Guinea Bissau (González et al. 2017) found that electric fences deterred hippopotamus Hippopotamus amphibius entry into fields. The proportion of fenced fields where hippopotamuses were detected (1.3%) was lower that of unfenced fields (80.0%). Hippopotamuses were monitored in 100 rice fields in 2008–2011 in Orango Islands National Park and Uno Island and, in 2012–2013, in Cacheu National Park. Seventy-five rice fields had electric fences and 25 were unfenced. Fences were 80 cm high, were made out of 2.5-mm-diameter aluminium wire, connected to an energizer unit. Fences also comprised rope between wooden stakes, with strips of red and white striped plastic at 1-m intervals. Vegetation was cut from within 2–3 m around the wires twice each week. Fenced and unfenced fields were surveyed every 3–4 days for hippopotamus footprints.
- Tierson W.C. (1969) Controlling deer use of forest vegetation with electric fences. The Journal of Wildlife Management, 33, 922-926
- McKillop I.G. & Wilson C.J. (1987) Effectiveness of fences to exclude European rabbits from crops. Wildlife Society Bulletin, 15, 394-401
- Wilson C.J. (1993) Badger damage to growing oats and an assessment of electric fencing as a means of its reduction. Journal of Zoology, 231, 668-675
- Huygens O.C. & Hayashi H. (1999) Using electric fences to reduce Asiatic black bear depredation in Nagano Prefecture, central Japan. Wildlife Society Bulletin, 27, 959-964
- O'Connell-Rodwell C.E., Rodwell T., Rice M. & Hart L.A. (2000) Living with the modern conservation paradigm: can agricultural communities co-exist with elephants? A five-year case study in East Caprivi, Namibia. Biological Conservation, 93, 381-391
- Seamans T.W. & VerCauteren K.C. (2006) Evaluation of ElectroBraide™ fencing as a white-tailed deer barrier. Wildlife Society Bulletin, 34, 8-15
- Honda T., Miyagawa Y., Ueda H. & Inoue M. (2009) Effectiveness of newly-designed electric fences in reducing crop damage by medium and large mammals. Mammal Study, 34, 13-17
- Davies T.E., Wilson S., Hazarika N., Chakrabarty J., Das D., Hodgson D.J. & Zimmermann A. (2011) Effectiveness of intervention methods against crop-raiding elephants. Conservation Letters, 4, 346-354
- Honda T., Kuwata H., Yamasaki S. & Miyagawa Y. (2011) A low-cost, low-labor-intensity electric fence effective against wild boar, sika deer, Japanese macaque and medium-sized mammals. Mammal Study, 36, 113-117
- Otto T.E. & Roloff G.J. (2015) Black bear exclusion fences to protect mobile apiaries. Human Wildlife Interactions, 9, 78-86
- González L.M., Montoto F.G., Mereck T., Alves J., Pereira J., de Larrinoa P.F., Maroto A., Bolonio L. & El Kadhir N. (2017) Preventing crop raiding by the vulnerable common hippopotamus Hippopotamus amphibius in Guinea-Bissau. Oryx, 51, 222-229