A National Perspective on Feral Swine

A NATIONAL PERSPECTIVE ON FERAL SWINE

JAMES E. MILLER, National Program Leader, Fish and Wildlife, Extension Service,
USDA, Room3871 South Building, Washington, D.C. 20250

Status and Perspective

A general perspective on feral swine across the United States is somewhat akin to one’s perception of beauty and often described as being in the eye of the beholder. Feral swine, although rarely described as beautiful, may be good, bad, ugly or of no significance. According to Walker’s Mammals of the World (Nowak 1991), the first swine (Sus scrofa L.) in the United States were those brought by the Polynesians to Hawaii around A.D. 1000, and those introduced by the Spanish to the southeast in the early 16th century. Some of these earliest introductions provided genetic pools for several valuable domestic breeds as well as for the many feral populations introduced in other parts of the world.

There are other references (Towne and Wentworth 1950) who credit Christopher Columbus with introducing eight head of swine to the West Indies in 1493 on his second voyage across the Atlantic. These authors also credit Hernando DeSoto with 13 head of swine brought to Florida from Cuba in 1539 and thought to have been descendants of those introduced by Columbus.

Regardless of the source of introduction and relocations over the past 500 years, or whose account is most accurate, current estimates of feral swine in the United States are over two million animals in 23 states. The Minnesota Board of Animal Health (Mackey 1992) conducted a 50 state survey of chief wildlife and livestock disease control officials who reported established feral swine populations in 23 states. Of these 23 states, only 12 reported population estimates, which when totaled, amounted to 1,916,350 animals. The remaining 11 did not estimate populations, however, several of these states (Alabama, Arkansas, Louisiana, Georgia and West Virginia) suspect populations of several thousands of animals. It is reasonable, therefore, to estimate that the present feral swine population in the U.S. exceeds two million animals.

Unlike more traditionally considered large game species such as deer, for which state natural resource agencies maintain annual season hunting dates, bag limits and harvest figures, feral swine harvest and population estimates, in most cases, are not closely monitored. In fact, in the 14 states where they are classified as an animal which can be hunted by license holders, several of these states have a year-round open season with no bag limit on harvest and no special fee or permit requirement. In the Minnesota survey (Mackey 1992), 14 state officials who responded noted that they currently have a ban on the importation/introduction of feral swine into their states. If one were to poll sportsmen, private landowners, wildlife and livestock officials in states both with and without current feral swine populations, the opinions, concerns and philosophies would be mixed. Although there has been considerable research conducted on feral swine across the U.S. and in other countries, there is a diverse perspective about the status and management of feral hogs. There is a continuous critical need to inform people with factual information about feral swine and the known potential positive and negative effects.

Management Concerns

Prevention of the introduction and establishment of feral swine in states with no known feral swine populations is one of the management concerns of state natural resource agencies. As previously noted, 14 states currently have some type of ban or prohibition on such importation and introduction. However, not everyone acknowledges existing bans or regulations. Some people who might introduce feral swine may be well-meaning, but ignorant of the ban, if one exists, in their state. Others ignore laws or regulations because they like the idea of another species to hunt regardless of their potential impact on the ecosystem, other wildlife, domestic livestock, or damage to crops or forest lands.

Two major concerns about feral swine shared by professional wildlife managers and livestock officials as well as livestock producers are: (1) that feral swine are known to be very adaptable, have a high reproductive capability and, because of their feeding habits and behavior, can significantly impact wild ecosystems; and (2) that feral swine are known disease carriers. For example, Wood and Barrett (1979) identified five diseases known to have been found in feral swine in the U.S. that were contractible to either humans or domestic livestock.

Ecosystem Impact

Numerous studies (Wahlenberg 1946, Lucas 1977, Springer 1977, Wood and Brenneman 1977, Wood and Lynn 1977, and Lipscomb 1991) address the impact of feral swine on wild ecosystems. Other studies document direct impacts on native species via predation or consumption by feral swine (see Hanson and Karstad 1959, Springer 1977, Wood and Roark 1978). Wood, Woodward, Mathews and Sweeny (1992) noted that in personal communication with Joe Kurz of the Georgia Department of Natural Resources, a departmental study indicated that feral swine depredations resulted in the loss of 80% of sea turtle nests on Ossabaw Island. In a study by Wood and Barrett (1979), they concluded that the introduction or enhancement of feral swine populations in wild ecosystems was unsound. There are other studies that have been conducted in the U.S., as well as in other countries with feral swine, which document the depredation of feral swine on native wildlife and domestic livestock, and the impact on forestry, agriculture and the integrity of wild ecosystems.

Disease Reservoirs

It is well known among wildlife and livestock professionals that feral swine serve as highly mobile disease reservoirs for several contractible diseases. The two most serious diseases commonly found in feral swine are swine brucellosis and pseudorabies. Swine brucellosis, according to a revised United States Department of Agriculture Bulletin, “Wild Pigs – Hidden Danger to Farmers and Hunters” (Anon. 1992), is currently confirmed in 10 states in the U.S.; pseudorabies is in 12 states. Both humans and other domestic livestock (principally swine) can become infected via contact with brucellosis-diseased feral swine. Pseudorabies, despite its name, is not related to rabies and does not infect humans, however, it causes serious production loss to domestic swine producers. Once infected with pseudorabies, an animal is a life-time carrier and there is no effective treatment. It also can be transmitted, and often is fatal to other wild and domestic animals, including: raccoons, skunks, opossums, foxes, and rodents, as well as cattle, sheep, goats, dogs and cats.

Both federal and state laws govern the control of swine brucellosis and pseudorabies. The relocation of feral swine demands negative blood tests for these diseases. Anyone considering relocation of feral swine should first contact their state veterinarian. A recent survey of pork producers in Georgia conducted by the Southeastern Cooperative Wildlife Disease Study (Doster ed. 1992) indicated that 71% were aware that feral swine are often infected with swine brucellosis and pseudorabies. Five percent of the respondents reported feral swine on their land, 13% had feral swine within one mile of their land, and 27% had feral swine within five miles of their farm. They also reported that 9% had observed feral swine in contact with their animals and 1.5% had purchased wild swine in the past. Of these farmers, 6.5% of them, or their employees, hunted feral swine and 69% of the farms that had feral swine in the vicinity kept their domestic swine in outside pens.

The investigators concluded: the data reveals the need for a stronger public education program about feral swine for the pork industry as well as for sport hunters; and, although these findings came only from Georgia pork producers, they probably reflect the situation in a number of other southeastern states.

In a feral hog control study (Wood, et.al. 1992), of 589 feral hogs removed from a coastal plain habitat in South Carolina, swine brucellosis and pseudorabies were found in 13.9% and 9.7% respectively of those animals. Numerous other studies have indicated the incidence of these diseases in feral swine populations that can be transmitted to domestic swine. Quite often, feral swine show up in rural sale barns where the potential is high for infecting domestic herds. For this and other reasons, most swine farmers and livestock officials would like to see feral swine populations either eradicated or carefully monitored and controlled to avoid infection of domestic swine and resultant economic losses. It is important to note, however, that it is unlikely that either or both of these diseases would disappear even if it were possible to eradicate all feral hogs. For example, in the final report of the Feral Swine Meeting for Epidemiologists conducted in September 1992 in Arlington, Texas, a report (Anon. 1991) indicated that of 3,000 pseudorabies infected herds in the U.S., only 17 of those reported the most probable source of infection as contact with feral swine. And, of the 67 swine herds known to be infected with swine brucellosis in 1991, only six herds were infected as a result of contact with feral swine. However, in this same report, samples taken of feral swine on some private lands in Florida indicated high levels of pseudorabies-positive animals and fairly low levels of swine brucellosis-positive animals.

Damage Prevention and Control

Damage caused by feral swine can occur in many forms. Some common examples are: rooting and feeding on forest regeneration sites, row crop and pasture lands and food plots or plantings for wildlife; damage to ponds, tanks, springs and water holes; damage to wild ecosystems and threats to biodiversity; competition with other preferred wildlife species game and non-game; predation on other wildlife and domestic animals; and, disease threats to domestic livestock and humans. In addition, like deer and other large game species which cross highways, feral swine often cause not only damage to automobiles, but to their passengers when contact is made at high speed. Unfortunately, prevention of damage by feral swine in some situations on croplands is practically impossible without significantly reducing the swine population. For example, if agricultural crops or food plots are interspersed within habitats containing viable populations of feral swine, fencing costs may be prohibitive.

The best way to avoid potential damage problems with feral swine is avoid letting anyone introduce the animals into new areas. If they exist on property owned or managed by adjacent landowners, either fence effectively and monitor carefully, or use every legal means allowed to eliminate animals that move on to your lands. Fencing is expensive and not always effective unless carefully maintained. In fact, the only effective fencing I have seen included either six foot anchor chain fencing buried a foot underground or woven wire fencing surrounded by electric fencing. Therefore, except for protecting small areas, fencing is likely to be cost-prohibitive. Because of feral swine predation on lambs in Australia (Pavlov and Hone 1982) and the difficulty of control, some extensive efforts using electric fencing in lambing areas has been found to be effective as noted by Plant (1980).

Once established, control of feral swine populations, is usually difficult, quite expensive and rarely can be accomplished in a short period of time. In fact, over large areas of habitat, it may be virtually impossible to bring feral swine populations under control, or to eradicate populations. The animals’ high reproductive capability, their adaptability, their tenaciousness and the limited control methods add to the difficulty. In some areas, feral swine may be protected by open range livestock regulations.

As noted by Tipton (1977), population models and data from a Polish control program over several years demonstrates the difficulty of population control. What this and similar data and population modeling efforts illustrate is that not only does a significant portion of the population have to be removed to effect the following year’s population, but the effectiveness of control can vary greatly with food availability, weather conditions and natal mortality. For areas with considerable acreage and good distribution of feral swine, intensive population control for several consecutive years may be necessary to effect significant population reduction.

Effectiveness of control methods depends on the status of the regulations on the species in your state. For example, if feral swine are not considered a game species and can be taken year round, a combination of control methods, if legal, could be used. Hunting with dogs and shooting where legal and feasible, followed by a variety of trapping methods and snares, can be effective if diligently pursued in reducing populations. For additional information on feral swine control, see the “Great Plains Handbook on Prevention and Control of Wildlife Damage” chapter on feral hogs by Birmingham (1983). This handbook is in the process of being revised and is expected to be available later this year.

The economics of feral swine control vary due to methods allowable for use, intensity of control effort, and the geography of the area to control. A recent paper (Wood et.al. 1992) indicated that during a 19 month intensive study, 1987-1988, 589 feral hogs were removed at a cost of about $54 per animal. However, for a longer six year study effort, costs per animal removed were about $70. Clearly, the costs of control must be weighed against damage assessment estimates or other costs or values, such as recreational hunting if hunting is a management objective.

Recreational Uses

Hunting for feral swine is a very popular sport in some states. Based on my personal experience, the meat can be very good and can be prepared in a variety of ways. Proper precautions should be taken in processing and in cooking feral swine to avoid risks of disease.

In some states, the hunting of feral swine, particularly on private lands, whether for so-called Russian/European boar, razorbacks, or common feral swine, is a popular sport. However, in some areas, feral swine are taken incidental to hunting for other species. For some private landowners who charge either a daily or seasonal fee or lease annual hunting rights to others, they may feel that the return exceeds the known costs of damage or management costs. In some states where they are considered a big game animal, both state agencies and private managers practice various levels of management including harvest restrictions, season and bag limits, or require the purchase of special permits. Others. which may not classify them at all, may allow taking year round by any means as legal and only require a current hunting license.

The perspective of many agencies and managers is that natural mortality, disease, predation, hunting and trapping generally keep feral swine populations at stable levels. However, others, such as public and private land managers, work diligently either to keep populations low or to eradicate them. In some areas, where few, if any restrictions on hunting and trapping apply, it is possible to keep populations in check. Hopefully, additional research and monitoring capabilities will reveal better management technologies to assist land managers in decisions about feral swine.

Summary

Feral swine are well established in almost one half of the states in the United States. Considering their adaptability, reproductive capability, appeal to many hunters, and the difficulty and costs of control measures, it is likely that they will be with us for a long time. A review of the extensive research literature reveals that there have been many useful studies to help us learn more about these animals, yet we recognize the need to continue the search for better management tools and technologies. Land managers (private and public) continue to wrestle with the dilemma of management of feral swine.

Some of the improved management capabilities are needed for other species as well. For example, we need to find better means of population estimation and monitoring; we need better tools for prevention and control of wildlife damage and disease transmission; and, we need improved capabilities in managing habitats for all species in an ecologically balanced manner. We also need better capabilities to quantify the impacts of certain species on the ecosystem, not just of feral swine, but other populations such as white-tailed deer, beaver and coyotes.

Sharing existing knowledge and experience, the generation of continuing research and management knowledge, and other meetings to address management implications related to feral swine will benefit all of us. However, to be more effective in managing feral swine, responsible agencies and/or law makers may have to become more aggressive in establishing and enforcing needed regulations on feral swine relocation and control. Until this happens, wildlife managers across the nation with established populations of feral hogs will have to continue to try to achieve some ecological balance between population management, habitat capabilities and recreational use.

Literature Cited

Anon. 1991. Final report–feral swine meeting for epidemiologists 1992, Arlington, Texas. 17 pp. unpubl. report, U.S. Dept. Agric.

Anon. 1992. Wild pigs–hidden danger for farmers and hunters. U.S. Dept. Agric., Animal Plant Health Inspection Serv., Agric. Inform. Bull. No. 620, 7 pp.

Birmingham, G.H. 1983. Feral hogs. Pages D45 through D51 in R.M. Timm ed., Prevention and control of wildlife damage. Great Plains Agricultural Council, Univ. of Nebraska, Lincoln, NE.

Doster, G.L. ed. 1992. Wild swine disease awareness. SCWDS Briefs, October, 1992, Vol. 8, No. 3., pp. 3-4, Univ. of Georgia, Athens, GA.

Hanson, R.P. and L. Karstad. 1959. Feral swine in the southeastern United States. J. Wild. Manage. 23:64-74.

Libscomb, D.J. 1990. Impacts of feral hogs on longleaf pine regeneration. South. J. Appl. For. 13:177-181.

Lucas, E.G. 1977. Feral hogs: Problems and control on national forest lands. Pages 23-36 in G.W. Wood, ed. Research and management of wild hog populations. The Belle W. Baruch For. Sci. Inst. of Clemson Univ., Georgetown, S.C.

Mackey, W. 1992. A survey on wild hogs of the United States. Minnesota Board of Animal Health. 3 pp.

Nowak, R. M. 1991 Walker’s mammals of the world – 5th ed. pp 1337-1340. The Johns Hopkins Univ. Press. Baltimore and London.

Pavlov, P.M. and J. Hone. 1982. The behavior of feral pigs, (sus scrofa), in flocks of lambing ewes. Aust. Wildl. Res. 9:101-109.

Plant, J.W. 1980. Electric fences give pigs a shock. Agricultural Gazette of New South Wales Dept. of Agric. Vol. 91, No. 2.

Springer, M.D. 1977. Ecologic and economic aspects of wild hogs in Texas. Pages 37-46 in G.W. Wood, ed. Research and management of wild hog populations. The Belle W. Baruch For. Sci. Inst. of Clemson Univ., Georgetown, S.C.

Tipton, A.R. 1977. The use of population models in research and management of wild hogs. Research and management of wild hog populations. Pges 91-101. The Belle W. Baruch For. Sci. Inst. of Clemson Univ., Georgetown, S.C.

Towne, C.W. and E.M. Wentworth. 1950. Pigs from cave to cornbelt. Univ. of Okla. Press, Norman, OK. 305 pp.

Wood, G.W. and R.H. Barrett. 1979. Status of wild pigs in the United States. Wild. Soc. Bull. 7:236-246.

Wood, G.W. and R.E. Brenneman. 1977. Research and management of feral hogs on Hobcaw Barony. Pages 23-36 in G.W. Wood, ed. Research and management of wild hog populations. The Belle W. Baruch For. Sci. Inst. of Clemson Univ., Georgetown, S.C.

Wood, G.W. and D.N.Roark. 1978. Food habits of feral swine in the South Carolina lower coastal plain. J. Wild. Manage. 44:506-511.

Wood, G.W., L.A. Woodward, D.C. Mathews, and J.R. Sweeney. 1992. Feral hog control efforts on a coastal South plantation (In press). Proc. 46th Annu. Conf. Southeast Assoc. Fish and Wildl. Agencies. 20 pp.

Wood, G.W. and T.E. Lynn, Jr. 1977. Wild hogs in southern forests. South. J. Appl. For. 1(2):12-17.