Reproduction and Herpetofauna Depredation of Feral Pigs (Sus scrofa) at Fort Benning, Georgia
Type of DegreeThesis
Forestry and Wildlife Sciences
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The continued range expansion of feral pigs (Sus scrofa) in North America is an increasing cause for concern due to the numerous negative impacts that feral pigs can have on ecosystem structure and function. Once populations are established, feral pigs have proven to be extremely difficult to control, and close to impossible to eradicate. I examined two aspects of feral pig ecology: reproduction in conjunction with population control, and depredation of herpetofauna by feral pigs. If effective control and removal techniques are to be developed, it is critical to understand if feral pig populations respond to reductions in density that are associated with removal efforts by increasing reproductive output. I compared reproductive parameters and condition of adult sows that were collected between a control area and a treatment area where lethal removal occurred. From October 2004 to April 2006, we implemented a concentrated removal effort within the treatment area. Although the population density was 50% greater in the control area than the treatment area, I did not detect differences between areas for condition, litter size, ovarian mass, corpora lutea mass, and corpora lutea number. It is possible that several years of heavy mast production during the study may have negated any affect on condition and subsequent reproduction between the two study areas. These data suggest that reproductive parameters of feral pigs do not exhibit density-dependence during periods when pig populations are in good condition. However populations experiencing nutritional stress may be more reproductively responsive to reductions in density. With herpetofauna populations decreasing worldwide and the range of feral pigs expanding, the negative effect that feral pigs can have on threatened reptile and amphibian populations due to depredation could be substantial. From April 2005 to March 2006, I collected feral pigs (n = 68) with the use of firearms and examined stomach content for reptiles and amphibians. By estimating foraging time based on food passage rate and activity patterns, I was able to characterize daily and annual consumption rates of herpetofauna. I found 64 individual reptiles and amphibians, composed of 6 different species, which were consumed by feral pigs during an estimated 254 hours of foraging. Herpetofauna consumption showed distinct summer and winter peaks. Species (Anolis carolinensis) that are primarily arboreal became more vulnerable to depredation when temperatures were low due to their need to seek thermal shelter. Other species (Scaphiopus holbrooki) that exhibit explosive breeding behavior coinciding with mass terrestrial migrations also faced increased vulnerability to pig depredation. Results suggest that feral pigs are opportunistic consumers that can exploit and potentially have a negative impact on species that exhibit similar life-history characteristics as those species reported in this study.