Regional variation in demographics, reproduction, and body mass growth rates of wild pigs: Implications for population control

Abstract

Wild pigs are a destructive invasive species throughout many regions of the world and have proven difficult to control or eliminate. Their success as an invasive species is, in part, from their high reproductive potential, which can vary based on available resources, ancestry, and other factors. We opportunistically collected data on demographics (i.e., age and sex), reproduction, and body mass on 2,762 wild pigs throughout various research and operation control activities in Texas, Alabama, Hawai'i, Guam (USA), and Queensland (Australia) during 2016–2024. We evaluated these data for differences among study sites that might lead to a better understanding of wild pig ecology and more effective control of their populations. We found that the age structures of wild pigs varied greatly among sites, with areas with more intense control having younger populations. The timing and frequency of birth pulses also varied by site. Large disparities among populations demonstrated the elasticities of wild pigs in invaded ranges; for example, the Alabama study site had a mostly young population with fast body mass growth rates and 2 discernable birth pulses per year, whereas the Guam study site had an older population with slow body mass growth rates and an indistinguishable birth pulse. We hypothesized that intense population control may increase reproduction rates in younger females through increased body mass growth rates and subsequent reproductive maturity. We recommend that managers identify the seasonal birth pulses of wild pigs in their region, and then intensively focus on removing wild pigs during the 115 days (i.e., gestation period) prior to those birth pulses. This may be counterintuitive to managers that focus on trapping after observing a birth pulse, but it increases the probability of simultaneously removing pregnant females and any associated offspring from previous litters that remained with the pregnant female. We also recommend evaluating regional-specific intensities of removal that might be required for reducing populations with specific emphasis on whether compensatory reproductive behaviors are generated and how to avoid them.