HISTORY OF THE INVASION AND CONTROL EFFORTS
The European wild boar first appeared in the 1940's in the southwestern corner of the park, and since has spread westward to occupy all but portions of the southeastern corner (Bratton 1974; pers. corres.). Temporary intrusions have been observed as far as Cataloochee in the questionable area (Tom Kluse; pers. corres.) (Figure 1). The invasion pattern may have been complicated by the presence of feral domestic swine around the border of the park and by introductions of European wild boar into nearby hunting lands.
The rate of invasion was 44 km from 1948 (approximate) to 1972 or 1.8 km per year, but greatly increased between 1972 to 1975 when pigs crossed Highway 441 and arrived in Cosby (8 km per year). This last eruptive burst was no doubt influenced by introduction of boar outside of Cosby where residents were reporting damage in 1973, the same year boar reportedly crossed Highway 441 near Sugarlands. In comparison, Caughley (1970) reported on a similar eruption of introduced Himalayan thar (Hemitragus jemlahicus) into new range in New Zealand at an average rate of 1.1 km per year.
Habitat is quite different in the eastern portion of the park at higher elevations. Whittaker (1956) described more extensive blocks of spruce-fir habitat and the occurrence of spruce fir forests at lower elevations than in eastern areas. S. P. Bratton (pers. corres.) has suggested that these more massive blocks of spruce-fir are poorer habitat for boar and their presence may have a significant effect upon boar invasion rates and patterns. Chris Egar (pers. corres.) analyzed some 40 spruce-fir stands in the park in 1976 and observed no hog rooting, although rooting was common in adjacent beech/birch stands west of Highway 441.
The history of the control effort was compiled from Park Service records kept in the office of the Resources Manager. It is known that the records are incomplete, especially for records of any animals shot during the periods when it was agreed to trap and transport all boar to the adjacent states. The magnitude of the under-estimating bias is not known.
Control efforts began in 1959, when the rooting of western grassy balds, Parsons and Gregory, received attention in local newspapers and amongst the park staff. From 1959 to 1975, 927 boar were taken in the park through the control program. Of the 927, 626 (67.5 percent) were trapped and 301 (32.5 percent) were shot.
The yearly breakdown of boar taken is provided in Figure 2, along with corresponding guesses (not estimates) of the population size in 1959 and 1976. The 1959 figure is provided by Linzey and Linzey (1971) and the 1976 guess was based upon population estimates for nearby Tellico Game Management Area (R. Conley, pers. corres.) extended for the 80 percent of the park now occupied by boar. Habitat differences between the two areas are numerous, but wide distribution of boar in the area involved, the fact that the population is lightly harvested, and preliminary census work in 1976, all tend to support the 1,920 estimate.
Figure 2 is oversimplified. European wild boar are known to fluctuate greatly in numbers in response to mast crop and weather, and apparently have done so in the Great Smoky Mountains (Duncan 1974; K. Higgins pers. corres.). Rate of increase was probably exponential. The estimates suggest that the Park control program has probably never taken more than 8-13 percent of the population present, based upon the best guesses available at this point. Bratton (1974b), based upon a review of European literature on the wild boar, suggested that harvests of at least 25 percent would be needed to stabilize a population and harvests of 50 percent to reduce it. The actual level of harvest needed varies between years in relation to weather and mast crop and in relation to the sex and age classes taken.
The locations of boar taken in the control programs are presented in Figure 3; many locations could not be found. Boar were primarily taken at lower elevations, in off-season (late fall to early spring), and primarily along access roads. These patterns reflect the part-time status of the control work for regular Park Rangers and Fire Control Technicians.
Fox (1972) evaluated the efficiency of control techniques in the park. Trap efficiency, with the types used, was very low (1.4 percent success rate for trap nights), but was significantly increased if the trap was placed near fresh hog sign. The most efficient technique was hunting at night while walking (9.7 man hours per hog removed). In addition, other wildlife speciescrows, raccoons, turkeys, white-tailed deerwere active at the trap sites and reduced trap success. Boar removed by shooting were usually mature animals. Immature animals were often taken by trapping, the amount depended upon the timing of farrowing periods.
The control program in the Smokies yielded a total of 502 (54.2 percent) females and 425 (45.8 percent) males. Weight classes (age was not determined) suggested similar age selection to the aged sample of Duncan (1974). Information on the sex and age distribution of the free ranging population is lacking, however, these data are similar to other known populations, and suggest that the control program was unbiased towards sex and age groups. Eastern Tennessee is characterized by a high proportion of yearlings. For example, yearling classes were 21 percent in the park (Duncan 1974), 23.4 percent in nearby Tellico (Conley et. al. 1972), as compared to 9 percent in Poland and 13 percent in the Soviet Union (Sludski 1956). Both Tennessee populations are expanding (Tellico is heavily harvested) and are not subject to wolf predation. The survival rate of yearlings is apparently excellent.
Last Updated: 24-Aug-2009