Environmental Engineering Reference
In-Depth Information
animals are truly absent. Those levels are typically based either on the costs of being
wrong (if these are unknown) or refl ect some arbitrary level of managerial comfort
(Ramsey
et al
. 2009). Managers have to compare the risk of wasting money on
extra monitoring or control when in fact no pests remain, with the risk of falsely
declaring the pest absent when in fact some do remain (e.g. Regan
et al
. 2006).
Pest populations can be prevented from spreading and their adverse impacts man-
aged by establishing physical barriers, usually in the form of fences. Thousands of
kilometres of dingo fence have been built in Australia (Allen and Sparkes 2001), and
barriers are widely used in Africa to control large herbivores, especially elephants
(Boone and Hobbs, 2004). Fences can also be used to help maintain control or
locally eliminate populations within areas already occupied by the pest, by reducing
the rate of reinvasion from unmanaged areas. This approach is particularly useful
where the animals are managed for different purposes on adjacent lands (e.g. eradi-
cation of pigs from nature reserves on Hawaii that are adjacent to areas where they
are managed for hunting; Katahira
et al
. 1993). Predator-proof fences capable of
preventing animals as small as mice from regaining entry to areas from which they
have been eradicated (McLennan 2006) have become something of a cornerstone
to private conservation efforts in New Zealand. The principal limitations of fences
are that they do not directly reduce the numbers of pests; they are expensive to build
and maintain, and always eventually leak. The consequences of the latter in terms of
the costs of detecting and dealing with breaches compared with unfenced sustained-
control alternative strategies have yet to be revealed by events (Anon 2007).
Tools to control vertebrate pests are older than written records, with snares and
traps, slings and arrows, toxins, and biocontrol agents (the pet cat in Egyptian
granaries) all used long before modern science became interested, and after best
practice manuals made at least some, such as magic, redundant—well, not quite
redundant but quaint and equally useless (e.g. homeopathic remedies; Eason and
Hickling 1992). It has been said (reputedly by Ralph Waldo Emerson) that if you
build a better mouse trap the world will beat a path to your door, and the develop-
ment of new control tools remains a busy industry. The modern trends for devel-
oping control tools are generally to increase effectiveness, replace cruel methods
with those that are less cruel, and to improve target specifi city.
12.3.3.1 Snares and traps
The basic principles of snares and traps (for convenience we call them all traps) have
not changed for millennia. Mascall (1590) described over 30 traps and one lure
used to trap pests such as foxes in England in the 14th century, while Proulx (1999)
categorized the plethora of traps used in North America in the 20th century—
the basic difference being the later focus on humaneness (and hygiene), without
