Reduction of feral pig Sus scrofa numbers reduces damage to seepage slope habitat at Eglin Air Force Base, Florida, USA

  • Published source details Engeman R.M., Stevens A., Allen J., Dunlap J., Daniel M., Teague D. & Constantin B. (2007) Feral swine management for conservation of an imperiled wetland habitat: Florida's vanishing seepage slopes. Biological Conservation, 134, 440-446


Only 1% of the original extent of Florida's seepage slope habitat remains. Seepage slopes are boggy grassy meadow or shrub thicket wetlands at the base of a slope, and are maintained by downslope groundwater seepage from a perched water table (i.e. above an impermeable clay or rock layer). Many rare and endemic plants are found in seepage slopes. Eglin Air Force Base (Eglin AFB) in northeast Florida supports some of the largest remaining seepage slope tracts, but a major threat is damage caused by feral pigs Sus scrofa. A study was undertaken to assess the extent of pig damage to seepage slopes on Eglin AFB, and evaluate the impacts of sport hunting and pig removal in damage reduction.

Study sites: In spring of 2003, 28 of 237 seepage slopes in Eglin AFB were selected for study. To evaluate the impact of public sport hunting on pig damage, 50% (14) of the seepage slopes were randomly selected from areas open to hunting, and 50% in areas closed to hunting (pigs were free to roam among areas).

Habitat monitoring: Pig damage (broken vegetative surface caused by rooting or trampling) and habitat variables were measured at 20 randomly selected 1 m² plots within each seepage slope in May/June of 2003 (prior to initiation of pig removal), 2004, and 2005.

The number of plant species in each plot was also recorded, as well as several other vegetative variables. Of special interest was the percent cover of toothache grass Ctenium aromaticum, wiregrass Aristida beyrichiana (as coverage by these grasses is an indicator of seepage slope health), and herbaceous cover (including several state-listed threatened and endangered species).

Pig population indices: Pig numbers were monitored using a passive tracking index methodology. Tracking data were collected from 17 permanent plots in September 2003 just prior to implementation of removal, and subsequently in these plots, plus an additional 11 in September 2004 and 2005, after one and two years of removal.

Pig removal: Removal was initiated in autumn 2003 in the area closed to hunting. Removal was and has continued with agreement with the US Department of Agriculture/Wildlife Services (the agency responsible for managing conflicts with wildlife).Only approved and humane methods of catching and euthanizing animals (conforming to strict veterinarian guidelines) are used. Pigs were primarily removed by capture in pen traps, but some were taken out by control hunting.

Initial pig damage estimates: In May/June 2003, prior to prior to initiation of pig removal, pig damage resulted in losses to seepage slopes in the section of the base closed to hunting of 25.0%; in that open to hunting losses were estimated at 10.9%.

Pig damage estimates after removal: In the 1.7 years (autumn 2003-2005) after implementing removal, 631 pigs were removed from the unhunted areas; 92 pigs were taken out by sport hunting. After less than one year of pig removals, damage in the closed-to-hunting area had dropped from 25.0% to 7.2%. Although removal was not applied in the open hunting area, damage dropped from 10.9% to 5.6%. After another year of removal, average damage had dropped again in both areas: in the closed hunting area to 5.6%; in the open hunting area to 4.3%.

Thus although removal was only applied to the area closed to hunting, it also produced damage reductions in the open hunting area. Declines in damage following implementation of removal corresponded with large drops in the pig population indices for the Eglin AFB.

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