Developing an Electrified Fence to Exclude Rabbits from Crops

The effectiveness of a new design of electric strained wire fence (CSL fence) for managing rabbits is currently being assessed in a two year trial. It is being compared with a commercially available electric netting fence (Flexinet fence) and also with farmers' normal control methods. The study is taking place on commercial farms in Cornwall, England, where the fences are being erected to protect fields of cauliflower. The amount of rabbit damage to individual plants in each field is being assessed and the numbers of rabbits feeding in these fields are being counted. Plant yields at harvest will also be used to determine effectiveness. Observations of rabbit behavior at the CSL fence are being conducted to identify potential design problems and to assess solutions to these problems. There was no difference between the effectiveness of the two fences during the first six months of the trial. Few plants were completely eaten by rabbits in the protected fields (CSL fence: 5_+6%; Flexinet fence: 0%) but, by contrast, most were eaten at the control sites (82_+17%). No more than a single rabbit was ever counted at night on the CSL(0.7+.0.1 rabbits) or Flexinet(0.5.+.0.2) protected sites but up to 20 (17.0_+3.0) were counted on the control sites. The few rabbits which were observed crossing the CSL fence either jumped through or over it. The CSL fence design is proving to be extremely cost-effective and in this trial it would already have recouped its costs many times over if it had been used to protect the control fields. It will be further tested next year. The research was funded by the Horticultural Development Council. Proc. 16th Vertebr. Pest Conf. (W.S. Halverson& A.C. Crabb, eds.) Published at Univ. of Calif., Davis. 1994. INTRODUCTION The European wild rabbit (Oryctolagus cuniculus) has once again established itself as the major vertebrate pest of crops in Britain causing damage estimated to cost farmers tens of millions of pounds every year (Rees et al. 1985). Recent surveys have shown rabbit numbers to be increasing (Trout et al. 1986) mainly due to the waning effects of myxomatosis (Ross and Tittensor 1986). Therefore, the development of more cost-effective methods of control has become increasingly important. Wire mesh fences have been in use for many years to protect crops from grazing by rabbits (McKnight 1969). More recently, electric fences have also been developed for this purpose. In Britain, there are two types of electric fence commonly used to manage wildlife. One is electric netting fences which are sold as ready-made fences with specific designs being recommended for specific species. The other is electric strained wire fences which are sold in their component parts (wire, posts and insulators) for farmers to construct their own designs to manage one or more species simultaneously. Research has shown that electric netting fences marketed for rabbit management are as effective as conventional unelectrified wire netting, each excluding about 80% of rabbits (McKillop and Wilson 1987, McKillop et al. 1988). Purchase and erection costs of electric netting fences are, however, about 60% less than those of wire netting (McKillop and Wilson 1987, McKillop et al. 1988). The costs of the design of electric strained wire fence most frequently recommended by fencing companies to manage rabbits are similar to those of electric netting fences. However, when this design was tested in enclosure trials, it was about 30% less effective than electric netting (McKillop et al. 1992). The Central Science Laboratory (CSL) has subsequently conducted a series of enclosure trials to develop a more effective design. These trials resulted in a fence which was 97% effective (McKillop, unpublished). However, rabbit behavior in the unfamiliar environment of an enclosure could be different from that in the familiar environment of their own home range. We, therefore, began a twoyear field trial in July 1993 and, in this paper, we report the results of the first six months of that trial in which the fence was being used to protect fields of cauliflower from grazing by rabbits. Its effectiveness was compared with a previously untested electric netting fence (Flexinet Super Rabbit Netting) and with farmers' normal control methods. MATERIALS AND METHODS The Fences The CSL fence was 0.4 m high and consisted of five parallel steel wires 2 mm in diameter at heights of 5, 10, 20, 30 and 40 cm above the ground. The bottom wire was earthed and the upper four conducted current. At one site, additional wires were added during the trial at 15 and 25 cm. The Flexinet fence was 75 cm high with an 75 x 65 mm mesh. The horizontal strands were made of polythene twine and, with the exception of the bottom strand, contained three 0.2 mm stainless steel wires which conducted the current. This type of wire is known as polywire. The vertical strands were made from nonconducting twine. Each fence was powered by a Speedrite battery-operated energizer which produces an energy output of 1.5 J, into a resistance of 500 ohms, and a maximum voltage of about 6 kV. Fences were erected along field boundaries to enclose completely the study fields. Shorting of the fence by vegetation growth was prevented by spraying the herbicide Gramoxone (paraquat) along the length of each fence to clear a strip about 0.5 m wide. CSL fences were on average about 480 m long (range: 350 to 750 m) and Flexinet about 650 m (range: 600 to 700 m). Routine monitoring of the fences was conducted by local growers.