Depredation Problems Involving Feral Hogs

ROBERT BEACH, Assistant State Director
Texas Animal Damage Control Service, San Antonio, Texas


Abstract: The feral hog population in Texas constitutes an introduced exotic species. If not properly managed, this exotic species has the potential of causing extensive damage to native wildlife, habitat and agricultural resources. Texas Animal Damage Control Service (TADCS) depredation report records are presented as a sample of the damage the feral hog is capable of inflicting.


The pig family (Suidae) is not indigenous to Texas. The hog (Sus scrofa) was introduced to Texas and became a feral population through a combination of accidental releases and intentional stockings (Mayer and Brisbin, 1991). Today, feral hogs are pervasive and abundant in the state and represent a remarkably successful exotic population.

There are both positive and negative aspects to the feral hog population in Texas. The hog’s Russian boar phenotype (S. scrofa spp.) is considered by some to be a trophy game animal with an edible carcass. California, Florida, Hawaii, Mississippi, North Carolina, Tennessee, and West Virginia afford feral hogs varying degrees of legal game status (Mayer and Brisbin, 1991). Some (Baber and Coblentz, 1987) even refer to feral hogs as the “most successful exotic big game species in North America”. In Florida, the feral hog has several times superseded the white-tailed deer (Odocoileus virginiana) in the number of animals taken under permit (Frankenberger and Belden, 1978). Although Texas does not give the hog legal game animal status, many landowners manage their feral hog populations as they do their white-tailed deer herds. The presence of feral hogs on a hunting lease is considered more of an added selling feature than a problem.

However, it may be short-sighted to consider only the positive aspects of this multi-faceted animal. There are numerous reports of severe problems with feral hog activities occurring in parks, recreational areas, national seashores, refuges, wildlife management areas, and forest districts across the United States (Lipscomb, 1989; Belden, 1972; Belden and Pelton, 1976; Scott, 1973; Jacobi, 1980; Baron, 1980; Lacki and Lancia, 1986; Willy, 1986; Wood and Lynn, 1977; Ralph and Maxwell, 1984; Singer et al, 1984; Ray, 1988). Land and wildlife management agencies are finding that the feral hog is an aggressive and difficult invader species that threatens their natural resources and habitat. Nevertheless, although the feral hog constitutes an invading “exotic” species, with a record of demonstrable damage to natural resources, it often has more support from the public than do many lesser known native species.

In reviewing the negative aspects of feral hogs, several questions should be considered. Does the feral hog population:

  • Compete with domestic animals and endemic wildlife for limited resources?
  • Prey upon fauna and flora to an extent that can be detrimental to the depredated species?
  • Represent a potential reservoir of diseases and parasites?
  • Have characteristics that threaten sensitive ecosystems (i.e., feral hog’s attraction to riparian habitat and the hog’s characteristic rooting and wallowing activities)?

It is important that we consider these concerns. The answers to these questions are significant factors we should address in the management of the feral hog population in Texas.

The feral hog is already widely dispersed across Texas. It has potential as both a problem species and game animal, and is today both hated and supported. We all need to become knowledgeable of the hog’s more disagreeable activities. This paper presents information gathered by the Texas Animal Damage Control Service (TADCS) dealing with damage caused by feral hogs. Until recent years, TADCS has not made a concerted effort to record data on depredations of feral hogs. However, data from 1982 through 1990 (Figures 1 and 2) illustrate some of the problems associated with feral hogs.

It should be emphasized that the figures presented represent only data from losses reported to TADCS by cooperating agricultural producers. Thus, these figures do not represent the total amount of damage caused by feral hogs to all resource owners in Texas. Unfortunately, we do not know what percentage these samples represent of the actual damage loss figure. A comparison of the Animal Damage Control (ADC) program’s nationwide fiscal year 1990 records of reported damage to published estimates of total damage caused by coyotes, indicated that 19 percent of sheep, 23 percent of lambs, and 36 percent of goats killed by coyotes in the United States were reported to the ADC program (Connolly 1992). Because coyote depredation is better recognized and more commonly handled by ADC, it is likely that a higher percentage of coyote caused resource losses are reported to ADC than are feral hog losses.

Depredation Problems

Problems caused by feral hogs are divided into six areas of focus:

  1. Feral hog populations cause damage to field crops. TADCS records show that feral hogs cause substantial damage to field crops in Texas. In one incident of peanut crop damage, $39,600 in production loss was attributed to feral hog activities. The variety of field crop resources damaged by hogs include, corn, milo, rice, watermelon, peanuts, hay, turf, wheat and other grains. Hog caused damage to field crops result both from feeding and from feeding related activities (i.e., trampling and rooting). A large percentage of the losses resulting from hog activities is additional to that loss resulting from the resource being eaten. As would be expected, the heaviest damage often occurs toward the end of the growing season when crops are, or nearly are, matured.
  2. Feral hogs prey on lambs, kids, fawns and ground nesting birds. Feral hogs can be efficient predators. While TADCS records indicate that feral hogs prey on all age classes of resource animals, most prey tend to be immature animals. The graphs in Figure 3 show the reported loss numbers of sheep vs. lambs, mohair goats vs. kids and other goats vs. kids, respectively. It should be again noted that these data represent only a sample of the actual losses. Also, the data are biased since remains of an adult animal are easier to find (i.e., thus report) than those of smaller animals.Feral hogs have an acute sense of smell, are omnivorous and opportunistic, and are thus frequently attracted to birthing grounds where they feed on afterbirths and fetal tissue. The pig also preys on healthy newborn lambs, kids and fawns, often removing newborn animals before they are seen by the producer and accounted for. Since hogs so thoroughly consume the young prey, there is often little evidence left to suggest that a birthing and subsequent predation has occurred. In effect the lambs and kids do not disappear, they fail to appear. There are no carcasses present to detect, examine, or attract vultures (Cathartes aura and Coagyps atratus). (Generally vulture activity is a helpful indicator of an ongoing predation problem.) So, if the resource owner is not alert to the possibility of hog predation, it is easy to overlook it as a cause for low production. Frequently, even when predation is considered, the pig escapes suspicion because people generally underestimate the hog’s capabilities as a predator.

    Even after it becomes apparent that hogs are consuming newborns (i.e., scat examination), there is difficulty with determining whether the hog is predating or scavenging. Without a carcass to examine, it is difficult to determine definitively whether the pig has killed a healthy newborn or has fed on a stillborn carcass or aborted fetus.

  3. Feral hog populations compete with resident deer and turkey populations for limited resources. Feral hogs are omnivorous and feed on a wide variety of items, many of which are staples for native fauna (Wood and Roark, 1980; Scott and Pelton, 1975; Baber and Coblentz, 1987). Thus, feral hog feeding activities can have a negative effect on the availability of food resources for both livestock and wildlife (Everitt and Alaniz, 1978 and 1980).One of the more important seasonal food item types for feral hogs is fruit/nut crops, especially oak mast (Wood and Roark, 1980). Oak mast is also an important food source for deer and turkey. When feral hogs actively compete for mast food (Yarrow, 1987), resident deer and turkey may enter the winter with deficient fat reserves.

    The pig has an advantage over deer and turkey in using oak mast. While deer and turkey feed primarily by sight and are limited to what is visible, the hog uses its keen sense of smell to locate the fallen crop. Thus, pigs have the ability to more thoroughly deplete an area of the mast than deer of turkey could do (Ray, 1988). Also, because the hog is omnivorous, it is able to switch to other available food items (e.g., roots) once mast is depleted (Scott and Pelton, 1975).

    Evidence that feral hogs compete with deer and turkey for food is demonstrated at automatic deer and turkey feeders. The TADCS annually receives reports from deer hunting operations that feral hogs consume corn placed out to bait deer and that the hogs’ activities cause deer to avoid the feeders.

  4. The feral hog population is a potential reservoir for numerous diseases and parasites that threaten livestock and deer. Feral pig populations are known to harbor diseases and parasites which can adversely affect livestock and deer. A recent study (Corn et al, 1986) involving 100 wild swine collected from 10 different feral pig populations in Texas found that feral pigs do represent a reservoir of diseases. Swine from several different counties tested positive for pseudorabies, brucellosis, and leptospirosis. African Swine Fever (ASF) is known to exist in South America (Ray, 1988), and the possibility of ASF spreading into North America is greatly increased by the presence of feral pigs along the southern border. Other diseases carried by feral hogs include hog cholera, tuberculosis, bubonic plague, and anthrax (Taylor 1991).Because feral hogs tend to occupy the same areas as both deer and livestock, disease and parasite spread is possible. One of the most probable points of contact is communal watering holes. Due to its inability to thermoregulate, the hog is attracted to watering areas to wallow (Belton and Pelton, 1976). In areas where water is plentiful, a wallowed-out watering hole may be avoided by other animals. But, during times of drought and in areas where water is limited, all animals are often obliged to water from wallowed out watering holes. Infected pigs can spread parasites and diseases through both direct contact and by contaminating drinking water. For example, leptospirosis can be transmitted through contact with infected urine. Contamination of a watering hole with urine is consistent with the pig’s wallowing behavior.
  5. The feral hog’s rooting and wallowing activities damage pastures, spoil watering holes and generally deteriorate riparian habitat. Feral hogs are persistent in their rooting behavior. They methodically work an area until they have depleted the food item of interest. Given optimum conditions (i.e., pliable soils) hogs can do considerable damage (Barrett, 1982). Because they attack at root level, they can decrease survivability of some plant species. To the hog’s credit, rooting tends to increase the aeration and humus content of the soil (Wood and Lynn, 1977). Nonetheless, rooting upsets climax communities and can create an environment that favors less desirable invader species of plants (Jacobi, 1980).In addition to the damage done to pasture and seed crops, soil upheaval can also be a problem. Rooting can result in the creation of troughs and mounds which can lead to erosion and the undermining of structures. In areas of heavy rain, rooting can be responsible for considerable loss of soil through leaching and erosion. Where equipment, such as mowers and bailers, are dependant on level terrain, the creation of either mounds or troughs can have a detrimental effect (Wood and Lynn, 1977). In areas where drainage can be a problem the creation of troughs can lead to mud holes and bog areas.

    As mentioned earlier, pigs are attracted to water. The concentrated activity in and around stock watering facilities can lead to general degradation of the area and tainting of the water. Wallowing activities in stock ponds can result in severely muddied water, algae blooms, oxygen depletion, reduction in fish viability, bank erosion, and soured water.

    Riparian habitat can be devastated by rooting and wallowing behavior. This is particularly true when drought conditions concentrate large numbers of pigs into a limited riparian area. Excessive rooting can damage the banks, deplete the flora, muddy the water and result in a silt-ladened benthic substrate (Scott, and Pelton, 1975). The viability of aquatic fauna populations can be depreciated by feral pig activities.

  6. Feral hogs are destructive to livestock fencing. The type and quality of livestock fencing required to contain sheep, goat, and exotic animals is expensive. Such fencing has the dual purpose of both enclosing the resource and excluding possible predators. A breach in a fence results in the loss of the resource (i.e., escaped, strayed or killed resource animals), loss of resource security (i.e., infiltration of predators), and a cost to repair the fence. Feral hogs, through persistence and brute strength, can breach all but very aggressive and expensive fence designs, if there is any attraction (i.e., food, water or an avenue to either) on the other side. Unless the attraction is eliminated, damage to repaired fencing will likely recur as long as the area is inhabited by the hogs that caused the original damage.

Conclusion

The feral hog problem in Texas has been overlooked, underestimated or ignored.

However, hogs are too large, too prolific, too destructive, and too widely spread for wildlife managers to remain complacent about their future in Texas. As wildlife managers, we must insist that this introduced animal be recognized as an exotic species that requires proper management to ensure the well being of our native plants and wildlife species.

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