Management, demographic and dietary insights from 7 years of aerial shooting of feral pigs in an agricultural landscape
Stuart J. Dawson, Tracey L. Kreplins, Magdalena A. Zabek, Jim Hone, Peter J. AdamsContext
Feral pigs are one of the most destructive invasive vertebrate species in Australia. Aerial shooting is considered one of the most effective methods for causing a rapid reduction in feral pig density at a landscape scale.
Aims
We aimed to assess the effects of 7 years of annual aerial shooting operations in the northern agricultural region of Western Australia. We measured the catch per unit effort (CPUE) of aerial shooting operations and assessed demographic, reproductive and dietary characteristics of the feral pig population.
Methods
We used operational data, including number of animals culled, and hours flown, to measure CPUE, measured in pigs per hour across 7 years at four spatially independent shoot blocks. We performed necropsies on 1502 culled pigs, collecting a range of morphometric, demographic, reproductive and diet metrics.
Key results
Over the 7 years of control 13,554 feral pigs were culled, with an average CPUE of 48.10 pigs h−1. The CPUE increased over the course of control, with a mean annual population growth rate (r) of 0.16 (95% CI: 0.12–0.22). Males were larger than females (mean ± s.d., adult bodyweight of 56.1 ± 22.8 v. 46.4 ± 17.7 kg), and slightly older (12.8 ± 11.7 v. 11.8 ± 11.1 months). Probability of survival of feral pigs to 3 years old was 0.12. On average, 62.3% of sexually mature females were pregnant, the mean in utero litter size was 5.03 (±18.6 s.d.), and this increased 0.05 per year of age of the sows. Sows bred year-round with two peaks in births. Cereal crops, primarily wheat, were the most frequently consumed food items, along with green vegetation and lupins.
Conclusions
Aerial shooting of feral pigs in the region has not resulted in a decline in population density. This is likely to be due to the species’ high fecundity and strong juvenile survival rates. Further, there is no evidence that aerial shooting has caused any noticeable changes in demographic parameters over time.
Implications
These results highlight the need to assess additional or alternative approaches to feral pig control and to analyse trends in pig removals during management activities.