Costs and effectiveness of damage management of an overabundant species (Sus scrofa) using aerial gunning

Abstract

Context Management of overabundant or invasive species is a constant challenge because resources for management are always limited and relationships between management costs, population density and damage costs are complex and difficult to predict. Metrics of management success are often based on simple measures, such as counts, which may not be indicative of impacts on damage reduction or cost-effectiveness under different management plans. Aims The aims of this study were to evaluate the effectiveness of aerial gunning for the management of wild pigs (Sus scrofa), and to evaluate how cost-effectiveness would vary under different relationships between levels of damage and densities of wild pigs. Methods Repeated reduction events were conducted by aerial gunning on three consecutive days at three study sites. Using a removal model, the proportion of the population removed by each flight was estimated and population modelling was used to show the time it would take for a population to recover. Three possible damage–density relationships were then used to show the level of damage reduction (metric of success) from different management intensities and levels of population recovery, and these relationships were expressed in terms of total costs (including both damage and management costs). Key results Populations were typically reduced by ~31% for the first flight, ~56% after two flights and ~67% after three flights. When the damage relationship suggests high damage even at low densities, the impact of one, two or three flights would represent a reduction in damage of 2%, 19% and 60% respectively after 1 year. Different damage relationships may show considerable damage reduction after only one flight. Removal rates varied by habitat (0.05 per hour in open habitats compared with 0.03 in shrubby habitats) and gunning team (0.03 versus 0.05). Conclusions Monitoring the efficacy of management provides critical guidance and justification for control activities. The efficacy of different management strategies is dependent on the damage–density relationship and needs further study for effective evaluation of damage reduction efforts. Implications It is critically important to concurrently monitor density and damage impacts to justify resource needs and facilitate planning to achieve a desired damage reduction goal.

Exposure of a population of invasive wild pigs to simulated toxic bait containing biomarker: implications for population reduction

“…69,70 A study in Texas, USA found that 3 days of aerial shooting resulted in 66% reduction in populations. 71 However, as densities of wild pigs declined to fewer than two to six wild pigs per km 2 (i.e., similar to densities observed in this study), the efficacy of aerial shooting decreased drastically. 72 Reductions in populations from trapping had varied success, with reports of 62-83% reductions in populations that were exposed to traps, and 28% for the overall population using up to 330 trap nights.…”

“…For comparison with other methods in other ecosystems, aerial shooting of wild pigs in Australia resulted in nearly 80% reductions in populations of wild pigs (i.e., more than 6–10 wild pigs per km 2 ) in 5–9 days . A study in Texas, USA found that 3 days of aerial shooting resulted in 66% reduction in populations . However, as densities of wild pigs declined to fewer than two to six wild pigs per km 2 (i.e., similar to densities observed in this study), the efficacy of aerial shooting decreased drastically .…”

Use of unmanned aircraft systems (UAS) and multispectral imagery for quantifying agricultural areas damaged by wild pigs

“…Department of Agriculture, 2015). Future work includes estimating wild pig abundance near crop fields that have been damaged and establishing relationships between wild pig densities and amounts of damage (Davis et al, 2018).…”

Movement responses inform effectiveness and consequences of baiting wild pigs for population control

“…Wild pigs consume agricultural plants (Schley and Roper, 2003;Ditchkoff and Mayer, 2009), costing an estimated annual $USD 1.5 billion in crop damages and control costs in the USA (Pimentel 2007). Populations of wild pigs often are intensively controlled and hunted (Steen, 2006;Gamelon et al, 2012;Ditchkoff et al, 2017;Davis et al, 2018;Rosa et al, 2018) to curtail their extensive damage to agriculture and property, or reduce the risk of disease spread to humans and livestock (Mayer and Brisbin, 2009;Barrios-Garcia and Ballari, 2012;Bevins et al, 2014). In addition, hunting or trapping of wild pigs is also popular throughout most of their distributed range for food or sport (Henry, 1966;Ditchkoff et al, 2017;Rosa et al, 2018).…”