The control of fox movement by electric fencing


On the Sands of Forvie National Nature Reserve in Aberdeenshire, north-east Scotland, an electric fence was tested for the first time in 1974 as a barrier to foxes Vulpes vulpes predating sandwich terns Sterna sandvicensis and eider ducksSomateria mollissima. Following these initial encouraging results (for a summary see: ) the method was tested again in 1975.

On 20 February 1975, a 2,200 m electric fence was erected across the north sector of the spit (terns and eiders nested on the southern end), a month earlier than in 1974. The fence comprised three parallel steel wires spaced 15 cm apart, the lowest 15 cm above the ground. The wires were supported by nylon insulators on steel posts (spacing between posts varied from about 6 m on level terrain to 3 m on rough ground). It was charged by one 'Koltek Big Tom' fencer unit per 1,000 m of fence. The fence could not be extended onto the intertidal area at either end (as it would be short-circuited at each high tide). The fence was removed in August when nesting had finished.
A 50-m wide 'tracking zone' along the north side of the fence was established. The fence and the tracking zone were visited usually every 2-3 days. Fox tracks were mapped and attempts were made to distinguish between individual foxes.

In 1975 there were five fence crossings (none recorded in 1974) all of which appeared attributable to one individual. It jumped the fence on 21 February (three days after fence erection) and walked through the wires on 24 and 25 February. The main weakness was that some foxes bypassed the fence via the intertidal areas: of 28 tracks on the beach, 16 (57%) passed directly along the shore, the remainder first encountered the fence then moved along and around an end.

The fence reduced overall fox visits to the area to less than a third of their former frequency. Fox activity in the southern part of the reserve (where the terns and eiders bred – no details of any predation events given) was reduced to about 16% of that expected if there were no fence. Overall, the author concluded that that electric fencing although not fox-proof was effective; evasion of the fence possible at each end via the intertidal areas.
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