Review of the management of feral animals and their impact on ...

warren structure amenable to recolonisation. On <strong>the</strong> o<strong>the</strong>r h<strong>and</strong>, skilled operators may
destroy deep warrens effectively.
Surface refugia destruction
Rabbits in some parts <strong>of</strong> Australia prefer surface refugia even when warrens are
present (Wheeler et al. 1981, Williams et al. 1995). Habitat destruction in <strong>the</strong>se
situations may require <strong>the</strong> removal <strong>of</strong> <strong>the</strong> shrub layer, <strong>of</strong> exotic weeds such as
blackberry <strong>and</strong> debris such as logs, <strong>and</strong> can greatly enhance <strong>the</strong> efficiency <strong>and</strong>
effectiveness <strong>of</strong> control programs <strong>and</strong> slow recolonisation. This may be undesirable as
such refugia also provide important habitat for amphibians, reptiles, small mammals,
<strong>and</strong> ground dwelling or ground feeding birds. The relative benefits <strong>of</strong> this action for
enhancing <strong>the</strong> recovery <strong>of</strong> endangered or vulnerable species would need to be
carefully assessed against <strong>the</strong> risks to o<strong>the</strong>r native species if such action is proposed in
areas being managed for conservation purposes.
Shooting
Shooting can be a humane way <strong>of</strong> destroying rabbits but is rarely an effective means
<strong>of</strong> reducing populations. Shooting may be used by l<strong>and</strong> managers as a method for
maintaining control once populations have been substantially reduced by o<strong>the</strong>r
methods. Small numbers <strong>of</strong> survivors in difficult country can also be hunted with dogs
<strong>and</strong> guns. Although not highly regarded as a game animal, wild rabbits are probably
<strong>the</strong> largest hunting resource in sou<strong>the</strong>rn Australia. There are no published reports on
<strong>the</strong> size <strong>and</strong> value <strong>of</strong> sport hunting <strong>of</strong> rabbits. The commercial rabbit industry depends
largely on <strong>the</strong> supply <strong>of</strong> field-shot rabbits to processing works, however harvesting
efforts have no significant <strong>impact</strong> rabbit populations (Ramsay 1994). To maximise
returns, commercial hunters move to areas where rabbits are more abundant ra<strong>the</strong>r
than continuing to shoot rabbits in a lower density population. Many <strong>of</strong> <strong>the</strong> areas now
subject to commercial harvesting, mainly in <strong>the</strong> Rangel<strong>and</strong>s, are those where widescale
effective <strong>management</strong> with conventional control techniques such as poisoning,
fumigation <strong>and</strong> ripping are difficult to achieve in <strong>the</strong> short term, ei<strong>the</strong>r economically
or logistically (Williams et al. 1995)
Trapping
Leg-hold traps have been used to catch <strong>feral</strong> rabbits for many years. The use <strong>of</strong> <strong>the</strong>
traditional steel-jawed leg-hold trap for <strong>the</strong> control <strong>of</strong> rabbits is not advocated as <strong>the</strong>y
subject <strong>animals</strong> to unnecessary pain <strong>and</strong> suffering <strong>and</strong> this technique does not reduce
rabbit numbers significantly to be an effective control technique (Gibb et al.1969,
Williams & Robson 1985). Exceptions to this are where small isolated populations are
targeted, in which case barrel traps or s<strong>of</strong>t catch traps should be used (Korn & Hosie
1988).
Fumigation
There are two fumigation methods; pressure fumigation <strong>and</strong> diffusion fumigation
(Cooke 1981, Williams & Moore 1995). Toxins used for fumigation include
chloropicrin, carbon monoxide, carbon dioxide, calcium cyanide, <strong>and</strong> phosphine
(Hayward & Lisson, 1978, Williams et al. 1995). Pressure fumigation requires <strong>the</strong> use
<strong>of</strong> a pump to generate <strong>and</strong> force <strong>the</strong> fumigant throughout <strong>the</strong> warren. The fumigant
usually comprises a mixture <strong>of</strong> thick smoke, carbon monoxide <strong>and</strong> chloropicrin (Parer
& Milkovits 1994). During fumigation all warren entrances are sealed. Entrances
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