Environmental Engineering Reference
In-Depth Information
One of the most spectacular advances was the use of helicopters to fi nd animals
and then to shoot them from the machine. h is was fi rst perfected as part of a com-
mercial game harvesting industry for red deer (
Cervus elaphus
) and other ungulates
in New Zealand in the 1970s (Nugent and Fraser 2005) that also acted as an
eff ective control tool for these invasive species at least in non-forested areas (Parkes
2006a). Helicopter culling was the main method used in the eradication (success
to be confi rmed) of feral goats from Isabela and Santiago islands in the Galapagos
(Lavoie
et al
. 2007) and of feral pigs from Santa Cruz Island in California. In the
latter case, 77% of the 5036 pigs killed were removed by this method (Parkes
et al
. 2008b). Helicopter culling remains the main tool to sustain control on feral
horses, donkeys, camels, pigs and goats across vast areas of Australia (Wilson
et al
.
1992).
As with trapping, shooting can be useful as a stand-alone tool for control but
is seldom adequate for eradication because there are usually some areas of heavy
cover or other refuges in which shooting is not eff ective or permitted. Nonetheless
at least one current campaign relies entirely on shooting—an attempt to eradicate
ruddy duck (
Oxyura jamiacensis
) from Great Britain (Genovesi 2005). Shooting on
lakes has reduced the numbers but cannot yet kill 100% of the birds encountered
on each shooting occasion, creating a risk that eradication will fail because the
survivors become harder to kill and cause the funding agencies to lose heart, or the
campaign falls into Zeno's paradox—the number removed each time gets smaller
and smaller but can never reach zero. Eradication attempts can only succeed if
the proportion removed annually exceeds the maximum possible rate of increase
(Caughley 1977).
Hunting with dogs is another ancient human activity, and has long been used
in pest control. Modern developments build on old team-hunting methods and
dog training, and aim to ensure that no animals escape their fi rst encounter with
the hunters. h is prevents the development of dog- and hunter-shy survivors, as
occurred during the eradications of feral goats from Raoul Island. h ere team hunt-
ing was not used and the last few killed were aged females that had been present
during most of the 20-year campaign (Parkes 1990b). h e hunters involved with
this campaign subsequently developed a 'wall of death' technique; on Santa Cruz
Island, this involved a line of hunters and their dogs, in contact with and supported
by a helicopter, working systematically across the landscape. To limit the number
of pigs that escaped back through the hunting line the dogs were trained not to
all simultaneously chase the same pig—only those that fi rst encountered the pigs
did so, except where pigs attempted to break back through the line. h e helicopter
was used to try to mop up any pigs that escaped. Up to 83% of pigs known to be
present were killed using this method; the rest mostly by simultaneous helicopter
hunting (Parkes
et al
. 2008c).
12.3.3.3 Poisoning
Natural toxins have long been used by humans to kill prey or emperors, along with
use of natural antidotes, such as bezoar stones from goat stomachs, to avoid being
