" New South Wales Department of Agriculture, Veterinary Research Station, Glenfield, N.S.W.;

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1 Aust. Wildl. Res., 1983, 10, Evaluation of Fencing to Control Feral Pig Movement Jim one* and Bill ~tkinson " New South Wales Department of Agriculture, Veterinary Research Station, Glenfield, N.S.W.; present address: School of Applied Science, Canberra College of Advanced Education, P.O. Box 1, Belconnen. A.C.T "ew South Wales Department of Agriculture, Agricultural Research Centre, Trangie, N.S.W.; present address: Agricultural Research Station, Cowra, N.S.W Abstract Eight fence designs with and without electrification were tested for their ability to stop feral pigs crossing from one paddock to another.fences of 8:80: 15 hingejoints were pig-proof, whereas fences of 6:70:30 hingejoint or plain wires allowed some pigs to cross. Electrification of the fences significantly reduced the frequency of pig movement through fences to as little as 6.3% of test pigs. The behaviour offeral pigs relative to the fences and their implications are described. Introduction Fencing is used to protect crops, pastures and lambs from damage due to feral pigs. In Australia a number of authors have suggested fence designs to restrict the movement offeral pigs into crops and lambing paddocks (Pharoah 1976; Giles 1977; Mitchell et al. 1977; Plant 1980). In California electric fencing is used to restrict feral pig movement onto irrigated summer pasture (Barrett 1971; Patton 1974) and elsewhere to protect crops near wildlife refuges (Thompson 1977). Snethlage (1 967) suggested two designs for pig-proof fences in Germany. Despite the widespread use of a variety of fence designs none have been systematically tested. This paper reports a study to determine the effectiveness of eight fence designs in controlling feral pig movement. The fences were tested with and without electrification under controlled conditions to enable their effectiveness and pig behaviour to be clearly observed. A similar experimental appproach was used to test fences for coyote control (Gates et al. 1978; Thompson 1979), and rat control (Shumake et al. 1979). Methods Experimental Design Eight fences were tested in a randomized block design. The fences were arranged serially in a straight line consisting of two blocks each of eight fences. Each test fence was constructed as a 20-m side of a rectangular paddock 30 by 20 m. The other three sides were hingejoint fencing. The eight designs were tested as non-electrified fences twice, then as electrified fences twice. The interval between time replicates was 1 week. Electric fences were charged by a battery-powered energizer delivering 6000 V, and were checked daily. Fence Deslgn Eight fence designs were selected for testing, on the basis of those reported in the literature and used on farms. Not all reported fence designs could be tested because of logistical problems.

2 J. Hone and B. Atkinson s 32,j 0 DESIGN 1 LIVE EARTH :;rd DESIGN 2 EARTH EARTH w 0 DESIGN 3 DESIGN 4 I I DESIGN 5 I I 1 7 P DESIGN WOOD DESIGN 7 Fig. 1. Fence designs tested with feral pigs. View is from pig-side of fences, showing live stand-offwire in designs 1, 2, 5-7 and 8. Arrows indicate plain wires holding top and bottom of hingejoint. Hingejoint 6 : 70 : 30 had six horizontal wires and a total height of 70 cm, with 30 cm between vertical wires. The bottom of the hingejoint in design 7 was staked to the ground midway between posts. Post intervals are not to scale.

3 Fencing to Control Feral Pigs The fences are shown in Fig. 1. Designs 1-4 consisted of plain wires with wooden or steel posts. Designs 5-8 consisted of hingejoint with wooden or steel posts. In all fences the plain wire was 3.15 mm galvanized. All posts were 5 m apart, and for electrification the existing fence was earth-connected. Stand-off wires were placed 15 cm on the pig side of the fence. Design 1 was similar to a fence reported by Pharoah (1976). Design 4 was similar to that outlined by Plant (1980), and design 8 (unelectrified) similar to a fence reported by Tilley (1973). Experimental Animals Four feral pigs were simultaneously placed in each paddock: one adult male, one adult female, one juvenile male and one juvenile female. This was equivalent to 67 feral pigs per hectare; a very high density, providing a severe test of each design. The pigs were aged on the basis of weight, those over 30 kg were classed as adults, and those less than 30 kg as juveniles. All pigs were individually ear-tagged and randomized with respect to the fence behind which they were placed, both within and between time replicates. The pigs were allowed 100 h to cross the fence. Pasture and water was available in each paddock but no natural or artificial shelter or supplementary feed was provided. The experiment was conducted in winter and spring Observations The presence and absence of pigs and their behaviour relative to the test fences were recorded during the daytime observation periods, usually of 1-2 h. The behaviour of the pigs remaining in the paddocks was recorded at 1-min intervals. Six types of behaviour were recorded: feeding, resting, walking, aggression, sexual behaviour and self-care (drinking, urinating, defaecating, scratching and wallowing). A total of observations were recorded. Analysis The efficiency of the fences in controlling pig movements was evaluated by three methods, which evaluated the results differently though the analyses were not independent. The first analysis was of the percentage of pigs crossing fences, and the other two examined the time taken by pigs to cross fences. Pigs could cross very soon after being placed behind a fence or take many hours to cross. The interval could be ~mportant in feral pig control, suggesting how frequently fences should be inspected and when, after a fence is built, pigs that have crossed the fence should be controlled. Differences could be expected between pigs in their ability to cross fences. Two statistics were analysed: the time till the first pig crossed the fence, and a measure of how long all pigs took to cross a fence. The latter was calculated by adding the total pig-hours that pigs were in a paddock behind the test fences. As each of four pigs had 100 h to cross a fence, the maximum of pig-hours was 400. The percentages of pigs crossing fences were examined by a fixed-factor analysis of variance. The data were pooled over time replicates, because of small samples, and transformed to arcsine. Zero and 100% data were adjusted as outlined by Snedecor and Cochran (1967). The effects of design, electrification, blocks, design X electrification and design X blocks were tested against an error of 821 divided by the mean number of pigs per cell. This is the estimated theoretical error in the angular scale when all error variance is binomial (Snedecor and Cochran 1967, p. 328). The second analysis tested the time, in hours, until the first pig in a treatment crossed its fence. The data were examined by a fixed-factor analysis of variance after adding 1.O and transforming to common logarithms. The effects of design, electrification, blocks, time and the design X electrification interaction were tested against a pooled estimate of error. The third analysis tested the total pig-hours that pigs were behind the fences. The data were examined as in the second analysis. In each analysis differences between means were tested by least significant differences, if the analysis of variance showed a significant effect at the 5% level (Snedecor and Cochran 1967). Costs The costs of materials for each design (excluding labour, strainer posts and electric fence energizer) were calculated as the cost of materials per kilometre per pig restrained from crossing. The latter was estimated from data pooled over times and blocks. Results The hingejoint mesh of design 8 was the only pig-prooffence tested (Table 1). Other fence designs allowed at least 6.3% of feral pigs to cross. There were highly significant (P<O. 005)

4 502 J. Hone and B. Atkinson effects of fence design on the percentage of feral pigs that crossed fences (Table 1). More pigs crossed the plain wire fences (designs 1-4) than the hingejoint fences (designs 5-8). The percentage of pigs crossing was highly significantly (Pt0.005) lower (11.6%) with electrification than without (79.5%). All pigs crossed the non-electrified designs 1, 3 and 4. In contrast, when the fences were electrified the maximum percentage of pigs crossing was 25.0% (Table 1). There was a significant (Pt 0.05) effect of blocks on the percentage crossing. There were no significant interactions of design X electrification or blocks X design. Design 8 was not included in this or subsequent analyses, because no pigs crossed this fence. Table 1. The percentage of feral pigs crossing each fence, and the number of pig-hours that pigs remained behind each fence Within columns. percentages followed by the same letter are not significantly different. Values for pig-hours are geometric means: maximum possible hours Design Percentage of pigs crossing Number of pig-hours No. Total Non-electrified Electrified Non-electrified Electrified With electrification, the average time till the first pig crossed a fence (67.4 h) was highly significantly (Pt0.005) longer than with no electrification (8.4 h). There were no significant effects of design, blocks, time or design X electrification. Fig. 2. Frequency of electric shocks received by feral pigs in the first 5 h of exposure to electric fences. Solid and broken lines show the numbers of shocks in replicates 1 and 2 respectively. Time since pigs placed behind fence (h) There were highly significant effects of design and electrification (PtO.005) and their interaction ( Pt 0.05) on the pig-hours that pigs were behind the test fences. Table 1 shows the pig-hours for the design X electrification interaction. The data are geometric means calculated by retransforming the logarithmic-transformed data used in the analysis of variance. The significant interaction was due to differing increases in pig-hours following electrification. For example, there was a large increase for fence 4 but a much smaller increase for fence 6.

5 Fencing to Control Feral Pigs 503 Pigs crossed the fences by passing between wires, most commonly (1 3 of 25) between the bottom and second wires, which were at heights similar to a pig's snout. Eleven crossings were between the second and third wires and one between the third and fourth wires. No pigs were observed to go under or over fences. Not all crossings were observed or could be classified according to the wires between which pigs crossed. Pigs placed behind the electrified fences received 60.7% (54 of 89) of electric shocks in the first half-hour and fewer thereafter (Fig. 2). Of the 89 shocks observed 30 involved adult females, 2 1 adult males and 19 each for juvenile females and males. In response to these and other electric shocks, 89.8% (n= 88) of feral pigs vocalized and ran from the fence and 10.2% (n = 10) ran from the fence but did not vocalize. Some feral pigs repeatedly challenged the electric fence, but did not cross, while others then charged through it. There were no apparent effects of sex or age on the time taken by pigs to cross fences or on their reaction to electric shocks. The hingejoint mesh designs (5-8) were the most expensive (Table 2). However, the electrified version of design 4 had the lowest cost per kilometre per pig restrained. The results show that the effect of electrification was to greatly reduce this cost. Table 2. Costs per kilometre of fences tested, and their cost efficiencies Design Non-electrified Electrified No. Mater~al Cost per kilometre Material Cost per kilometre cost ($1 per pig restrained cost ($) per pig restrained The most common activity pattern of the pigs behind the fences was resting (50.4%), then feeding (43.6%) and walking (5.2%). Other behaviour patterns were aggression (0.4%), self-care (0.3%) and sexual behaviour (0.1%). There were few differences between sexes and ages, except that adult males were more often involved in aggression. Discussion The results show that electrification significantly reduced the number of feral pigs crossing fences. Most of the fence designs tested were not pig-proof. On the basis of these results the fences reported by Wright (1972), Pharaoh (1976). Giles (1977), Mitchell et a/. (1 977), Venamore and Hamilton (1 978) and Plant (1 980) are probably not pig-proof. These fences should, however, significantly reduce pig movement. A netting design with small holes, similar to that reported by Snethlage (1967) and Tilley (1973) is necessary to prevent pigs crossing. Farmers considering using fencing to control feral pig damage have to choose between modifying an existing fence or building a new one. Electrification is the cheapest and simplest method of modifying existing fences. Results from this study show that modifying existing fences by use of a stand-off live wire will significantly reduce the percentage of pigs crossing fences and increase the time taken to do so. The electrified fences of designs 5,6 and 7 were virtually pig-proof, but those of designs 1, 2 and 3 were not. Better results in terms of pig control and economics can be achieved by constructing new fences. Plant (1980) reported that he found no satisfactory method of electrifying existing fences, because of practical problems of wire placement and insulation. Farmers building a new fence will have to choose between an expensive pig-proof fence (design 8 unelectrified)

6 504 J. Hone and B. Atkinson and a cheaper, virtually pig-prooffence (design 4 electrified). Individual farmers will choose either fence on the basis of their own financial situation, and the level of feral pig damage. The economics of a fence depend on such factors as its efficiency at preventing crossing, initial and annual costs, area enclosed, perimeter length, life (in years) of the fence and the density and value of sheep, plants or whatever object is being protected inside the fence (Caslick and Decker 1979; Caslick 1980). Lambs and maturing crops are susceptible to feral pig damage for only 1-3 months per year. Protection could be provided by enclosing a small area for lambing or around individual crops, as has been suggested for protecting lambs from feral pigs (Plant 1980) and coyotes (De Calesta and Cropsey 1978). The size of the area enclosed is determined by lambing or cropping needs and by considering that the fencing costs per unit area decline exponentially as the area enclosed increases (Shumake et al. 1979). The frequency of pigs crossing most electric fences means that other control methods may be needed to supplement fencing for control of pig damage. The three analyses used in this study gave differing results. That was not unexpected, given the types of data and the factors measured. The percentages of feral pigs that crossed fences were the most useful statistics. The data on time showed that pigs crossed a fence very soon after being placed behind it. This indicates that feral pigs may be expected to cross a fence soon after it is built, and hence any control of those pigs should be conducted at that time. The data on the total pig-hours showed that some pigs stayed behind the fences for much longer than others. The results indicate the need to complete building fences well before cropping or lambing. Plant (1980) suggested fences should be completed 3-4 weeks before lambing. The way pigs crossed the fences was surprising, because they passed through rather than under. Feral pigs have been seen by both authors to pass under and through fences in the wild, and so designs 7 and 8 had the bottom of the hingejoint on the ground. On uneven ground the space between the wires and the ground varies and pigs may then be more likely to go under fences. The observations of pigs running through an electric fence after receiving repeated shocks were noteworthy. The pigs did not vocalize before crossing. McCutcheon (1980) implied that such crossing behaviour (with vocalization) had not been reported. It was clear from the observations that pigs quickly learn to avoid electric fences. Similar behaviour has been reported with rats (Shumake et al. 1979) and cattle (McDonald et al. 1981). Such learning is important to the long-term effectiveness of electric fencing. The activity data indicated that the pigs did not spend 100 h ofinactivity behind the test fences, but showed daily behaviour patterns like those expected of feral pigs in similar situations. Acknowledgments We would like to thank the farm staff, manager and director of research at the Agricultural Research Station, Trangie, for invaluable assistance throughout the study. H. Bryant, A. Burns and R. Pither in particular are thanked for braving the wet, icy winds of the plains. We also thank Mr P. Nicholls for statistical advice and J. Morris for drawing Fig. 1. Financial assistance was provided by the Australian Meat Research Committee. References Barrett, R. H. (1971). Ecology ofthe feral hog in Tehama County, California. Ph.D. Thesis, University of California, Berkeley. Caslick, J. W. (1980). Deer-proof fences for orchards: a new look at economic feasibility. Proc. 9th Vertebr. Pest Conf., Fresno, California. pp Caslick, J. W., and Decker, D. J. (1979). Economic feasibility of a deer-proof fence for apple orchards. Wildl. Soc. Bull. 7, De Calesta, D. S., and Cropsey, M. G. (1978). Field test of a coyote-proof fence. Wildl. Soc. Bull. 6,

7 Fencing to Control Feral Pigs 505 Gates, N. L., Rich, J. E., Godtel, D. D., and Hulet, C. V. (1978). Development and evaluation of anti-coyote electric fencing. J. Range Manage. 31, Giles, J. R. (1 977). Control of feral pigs. Wool. Technol. Sheep Breed. 25, McCutcheon, J. (1 980). Electric fence design principles. (Electrical Engineering Department, University of Melbourne.) McDonald, C. L., Beilharz, R. G., and McCutcheon, J. C. (1 98 1). Training cattle to control by electric fences. Appl. Anim. Ethol. 7, , Mitchell, T. D., Kearins, R. D., Marchant, R. S., and Plant, J. W. (1977). Electric fences to control feral pigs. Agric. Gaz. A:S. W. 88, 10. Patton, D C. (1974). Feral hogs - boon or burden Proc. 6th Vertebr. Pest. Conf., Anaheim, California. pp Pharaoh, D. M. (1976). Permanent electric fencing. N.S.W. Dep. Agric. Inf. Bull. No Rev. Ed. Plant, J. W. (1980). Electric fences will give feral pigs a shock. Agric. Gaz. NS. W. 91, Shumake, S. A., Kolz, A. L., Reidinger, R. F., and Fall, M. W. (1 979). Evaluation ofnon-lethal electrical barriers for crop protection against rodent damage. In 'Vertebrate Pest Control and Management Materials'. ASTM, STP 680. (Ed. J. R. Beck.) pp Snedecor, G. W., and Cochran, W. G. (1 967). 'Statistical Methods.' 6th Ed. (Iowa State University Press: Ames, Iowa.) Snethlage, K. (1967). 'Das Schwarzwild.' (Verlag Paul Pareg: Hamburg.) [Cited in: Bratton, S.P. (1974). An integrated ecological approach to the management of European wild boar (Sus scrofa) in Great Smoky Mountains National Park. U.S. Natl Park Serv. Manag. Rep. No. 3.1 Thompson, B. C. (1979). Evaluation of wire fences for coyote control. J. Range Manage. 32, Thompson, R. L.(1977). Feral hogs on national wildlife refuges. In 'Research and Management of Wild Hog Populations, Proceedings of Symposium.' (Ed. G. W. Wood.) pp Tilley, L. G. W. (1973). Pig fencing in Mossman. Cane Grow. Q. Bull. 36, Venamore, P. C., and Hamilton, W. D. (1 978). Don't let feral pigs eat your profits. Queensl. Agric. J. 104, , Wright, J. W. (1972). Electric fences to keep out wild pigs. Queensl. Agric. J. 98, Manuscript received 15 October 1982; accepted 11 January 1983