Chapter 28: Introduced wild pigs in North America309
As the most widely used form of population control on the
continent, lethal removal techniques have been the subject
of a number of studies in recent years seeking to improve the
efficiency and cost-effectiveness of these options. Such stud-
ies have been undertaken by government agencies, academic
institutions and private-sector commercial firms. A substan-
tial effort in this area has gone into the improvement of three
long-standing lethal removal options: trapping (e.g. trapping
protocol, overall trap design, trap gates/doors, trigger design,
remote/wireless tripping systems, baiting systems and bait com-
position), shooting (e.g. muzzle-blast suppression systems, sub-
sonic ammunition, night-vision and infrared sights and aerial
gunning protocol) and snaring (e.g. snare design and snaring
protocol) (Mayer & Brisbin 2009; West et al. 2009; Hamrick et al.
2011). Studies have also looked at improvements to the Judas pig
technique (i.e. using radio-collared wild pigs as a means to locate
other pigs for lethal removal through shooting) for controlling
these animals (e.g. Wilcox et al. 2004; McCann & Garcelon 2008;
Mayer & Brisbin 2009). In addition, novel mark–recapture tech-
niques using biomarkers have been developed to determine the
percent removal of a wild pig population using the aforemen-
tioned lethal methods (Reidy et al. 2011).
Since the late 1990s a lot of research has gone into the devel-
opment and registration of pig-specific toxicants for use in lethal
control of wild pig populations. These efforts are looking at toxi-
cants that can humanely kill pigs and yet have a benign impact
on non-target animals and the environment in general (West
et al. 2009). Related studies have also been underway to develop
a feeder to deliver an oral toxicant to wild pigs that would exclude
other species (Long et al. 2010). One study even looked at the
aerial delivery of these pharmaceuticals (Kavanaugh & Linhart
2000). This general area of research has also included the devel-
opment of bait design/composition to deliver these toxicants
(Campbell et al. 2006; Campbell & Long 2007). Biomarker or
tracer studies have also been conducted to evaluate the percent
of a population that such delivery systems would reach (Reidy
et al. 2008b). To date, however, no such toxicant has been regis-
tered for use on wild pigs in the USA (USDA-APHIS 2015); fur-
ther, the use of such lethal control options remains controversial
in this country (Bevins et al. 2014).
Another recently evolving area of research for reducing the
numbers of wild pigs in a local population has been the develop-
ment of a pig-specific contraceptive or reproductive inhibitor
(Mayer & Brisbin 2009; West et al. 2009; Hamrick et al. 2011;
USDA-APHIS 2015). Although studies with injected vaccines
have been very effective (e.g. Killian et al. 2003; Miller et al.
2004), the preference would be an orally delivered contracep-
tive. Research on the development of such reproductive inhibi-
tors is underway. In addition, research comparable to the feeder
delivery system and bait design/composition noted for oral toxi-
cants would also apply to oral contraceptives for wild pig control
(Hamrick et al. 2011; USDA-APHIS 2015).
Various options for the use of fencing to exclude wild pigs
have also been the subject of some recent research. This has
included the efficacy of types of fencing (e.g. Reidy et al. 2008a;
Lavalle et al. 2011) as well as specific fencing designs to exclude
wild pigs from access to deer and wildlife feeders (Rattan et al.
2010; Timmons et al. 2011).
Toward a better understanding of the impacts that these ani-
mals have on their host environments, research has also been
conducted on the damage that wild pigs cause. This has included
studies that characterize the damage (e.g. Mayer & Johns 2007;
Mayer 2013; Beasley et al. 2014) as well as studies that estimate
the economic impacts of such damage (e.g. Engeman et al.
2004; Pimentel 2007; Higginbotham et al. 2008; Shi et al. 2010;
Mengak 2012).
The successful management of wild pigs depends upon
persistent, adaptive, and integrated management programmes
that incorporate sound biological and ecological informa-
tion (Campbell & Long 2009). Toward that goal, studies have
been undertaken on the biology/ecology of wild pigs in North
America to improve the understanding of these animals as
well as the ability to control their populations. In some cases,
these efforts have repeated previously conducted studies; in
other instances, such replicated works are useful for evaluating
regional variation. Studies have varied from those addressing
the basic biology (e.g. Sparklin et al. 2009; McCann et al. 2014)
to those that conducted population modelling to determine bet-
ter manners in which to control the numbers of these animals
(e.g. Burton et al. 2012; Salinas et al. 2015).Conclusions
The saga of the wild pig in North America is continuing to evolve,
but remains unresolved from the invasive species management
perspective at the moment. Given the current inability to con-
trol either the numbers or spread of wild pigs on the continent,
the near-term future viewpoint regarding these animals will
likely require some level of acceptance of their presence in cer-
tain locations and areas. The conundrum of wild pigs being one
of the world’s worst invasive species combined with one of the
world’s most popular game animals will continue to complicate
efforts to successfully manage these animals on this continent.
This situation will also likely result in continued illegal releases
of wild pigs into unfenced areas, both to establish new popula-
tions and to increase existing ones. With respect to reducing the
numbers of these animals, the most promising techniques would
include pig-specific toxicants and contraceptives; however, both
of these options may not be available for some time to come or
be used in a widespread manner such that they are effective on a
continental scale. The ultimate success of efforts to address this
invasive species problem will require a combination of effective
control techniques, public understanding and acceptance of the
problem, legislative/legal support and international coopera-
tion, otherwise this issue will persist indefinitely. This has been
described as the greatest emerging wildlife management chal-
lenge that North America faces in the twenty-first century.Acknowledgements
This work was supported by the US Department of Energy Office
of Environmental Management under Contract DE-AC09-
08SR22470 to Savannah River Nuclear Solutions LLC..03012:52:20