Rabbits: Management options for preventing damage (TIN003)

Control Methods: Fencing

Fencing is a particularly useful management tool where the nature of the rabbit harbourage makes other techniques impractical, or when complete exclusion is the aim. In many situations, fencing can be more cost-effective than control methods that have to be undertaken year after year. Traditionally, permanent wire-netting fences have been used to deny rabbits access to vulnerable areas but more recently, temporary electric fences, either netting or multi-strand wire systems, have become popular methods of crop protection.

When correctly erected and maintained, wire-netting and electric fences can reduce rabbit numbers on protected fields by 85% to 90%, and both have a useful life of about ten years. Electric fencing is cheaper to purchase and erect than wire-netting, but its maintenance costs are higher.

Wire-netting

Netting fences should be constructed of 18 gauge, 31 mm (1 1/4 in) hexagonal mesh. They should be a minimum of 750 mm (2 ft 6 in) high with a further 150 mm (6 in) lapped on the surface of the ground towards the rabbit harbourage. Turfs of grass should be placed on the lapped netting at 1 m (about 1 yard) intervals to hold it firmly in place (vegetation should later grow through the mesh to complete this job). The netting should be attached to two 2.65 mm (1/8 in) high tensile spring steel straining wires (one at the bottom of the fence and one at the top) with galvanised fence rings. The straining wires should be supported by wooden stakes 1.8 m (5 ft 11 in) x 80 mm (3 in). The stakes can be placed up to 15 m (48 ft 9 in) apart although ground undulations may dictate closer spacing. End posts 2 m (6 ft 6 in) x 100 mm (4 in) braced by struts 2 m (6 ft 6 in) x 80 mm (3 in) should be placed at the ends of the fence and at bends.

Local site conditions or other considerations may demand a variation to these specifications. For example, particular attention should be paid to the presence of potential weak spots such as uneven ground, dry stone-walls and watercourses. In areas such as young farm woodlands, where it is especially important to prevent invasion by rabbits, the fence specification can be improved by projecting the top 150 mm (6 in) of the fence outwards at 45° towards the harbourage. It is recommended that any proposed changes to the specification are first discussed with one of Natural England's Wildlife Management Advisers (see Further information).

Ideally, wire-netting fences should be erected to surround fully the area to be protected. If this is not practical, a strip fence, which extends at least 150 m beyond either end of the problem area, may be used.

The number of gates in a fence should be kept to a minimum because they make maintenance more difficult. They should be hung on supports independent of fence straining posts, as the latter will inevitably move and so affect the hang of the gates. A wooden sill must be dug into the ground to prevent burrowing underneath, and gates should shut against a post. Badger gates should be installed in the netting if the fence crosses any badger tracks or paths.

An advisory leaflet, describing the design and installation of badger gates in rabbit-proof fencing (TIN026) is available (see under Further information).

Regular monthly inspections and maintenance of fences are essential to block burrows dug under the fences and to repair damage caused by farm machinery, fallen tree branches and vegetation. This safeguards the long-term effectiveness of the fence.

Electric fences

There are two types of electric fence in common use: netting and strained-wire. Both have been shown to be as effective as wire-netting fences.

Electric-netting fences are available in a number of commercial designs. Basically, they all consist of a heavy-duty polythene twine mesh in which the horizontal strands are interwoven with electrically conductive stainless steel wire. To prevent shorting, the steel wires are omitted from the bottom strand. They are between 0.5 to 0.75 m (1 ft 8 in to 2 ft 5 in) high and are supplied in 25 m (82 ft) or 50 m (164 ft) rolls in which the fence posts are already fitted. This type of fence is very quick and easy to erect and take down.

The electric strained-wire system consists of seven parallel electrified conducting wires (7-strand, 16 gauge medium tensile mild steel) at heights of 5, 10, 15, 20, 25, 30, and 40 cm (2, 4, 6, 8, 10, 12 and 16 in) above the ground. The lowest wire is earthed and the remaining six are live (a small length of wire should be wound around each of the top six wires to electrically connect them). Adjustable plastic insulators supported on metal stakes hold the wires. The stakes can be placed up to 7 m apart (about 8 yards), although ground undulations may dictate closer spacing. Where the fence line bends, anchor posts replace the normal metal stakes. The whole system is tensioned at a reel post placed at the end of the fence.

Both electric fence types must be powered by an energiser capable of producing an output of at least 1 joule when measured into a 500 ohm resistance. Most mains-operated energisers, and the more powerful battery-powered units, have this capability. Batteries should be changed regularly (a fully charged 70 Ah battery will need to be changed every 2 to 3 weeks). A wide range of energisers is available and users are advised to discuss specific requirements with their supplier. To effectively deter rabbits, it is important to maintain a minimum of 2.5 kV throughout the fenceline. A good earthing system is essential to achieve this.

Ideally, as for wire-netting fences, electric fences should be erected to surround fully the area to be protected. If this is not practical a strip fence, which extends at least 150 m beyond either end of the problem area, may be used. Prior to erection, a 450 mm to 600 mm (1 ft 6 in to 2 ft) wide strip should be mown along the fence line or the vegetation killed off using an approved herbicide. This ensures that the conducting wires are kept clear of vegetation that would otherwise short-circuit the system thereby draining power and reducing effectiveness. Initially, fences should be inspected every few days but this can later be extended to 2 to 3 week intervals.

A more detailed advisory leaflet on the use of fencing (TIN023) is available (see under Further Information).

ADLib logo Content provided by the Agricultural Document Library
© University of Hertfordshire, 2011