Cooperative Fish and Wildlife Research Units Program: Montana Wildlife
Education, Research and Technical Assistance for Managing Our Natural Resources

Wild pigs (Sus scrofa) pose considerable ecological problems as an invasive exotic. However, our understanding of many aspects of the ecology of this species is limited. Our goal was to examine the relationships between patterns of stress and reproductive behavior in a free ranging population of wild pigs through analysis of fecal glucocorticoid metabolites. We collected fecal samples from both trapped and hunter harvested animals between August 2004 and January 2006. Sexually mature pigs on Fort Benning had two seasons of elevated stress levels corresponding with two distinct periods of increased farrowing activity (March/April and July/August). For sexually mature females, fecal glucocorticoid levels were greater during the peak farrowing seasons than during the rest of the year. Fecal glucocorticoids in sexually mature males peaked during the periods immediately preceding each breeding season, and were at their lowest point during the peak farrowing seasons. Fecal glucocorticoid concentrations did not differ among sexually immature individuals of either sex between the breeding seasons and the rest of the year. Individuals collected from traps exhibited greater fecal glucocorticoid concentrations than individuals collected via hunter harvest. Mature males likely experienced their greatest levels of stress during the peak of the breeding season due to heightened breeding activity, and decreased stress during the peak of the farrowing season due to a decrease in breeding activity as the majority of receptive females were already pregnant. The timing of peak stress levels among both sexes of sexually mature animals and the lack of fluctuations in stress levels among sexually immature animals lead us to conclude that reproduction and the timing of peak reproductive activity are the major factors influencing stress among free-ranging wild pigs. This study has established baseline parameters of stress in wild pig populations, and highlights the temporal periods during which particular classes of animals experience the greatest levels of stress.