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

Competition
Several examples are recorded <strong>of</strong> pigs competing for food with birds in nor<strong>the</strong>rn
Australia. On Cape York Peninsula, pigs dig up <strong>and</strong> eat cockatoo grass (Alloteropsis
semialata), an important food <strong>of</strong> endangered golden-shouldered parrots, which face
food shortages at certain times <strong>of</strong> year because <strong>of</strong> changes in grassl<strong>and</strong> composition.
Crowley et al. (2003) note, ‘The period <strong>of</strong> food scarcity in <strong>the</strong> early wet season is
<strong>the</strong>refore likely to be longer <strong>and</strong> more severe where seed production by cockatoo
grass is reduced by pigs or cattle’.
When pigs plough through <strong>the</strong> mud around <strong>the</strong> edges <strong>of</strong> tropical lagoons <strong>the</strong>y are
<strong>of</strong>ten targeting <strong>the</strong> tubers <strong>of</strong> spikerush or bulgaru (Eleocharis dulcis), a staple food <strong>of</strong>
magpie-geese <strong>and</strong> brolgas. Within <strong>the</strong> Wet Tropics, pigs are thought to compete with
endangered cassowaries by consuming <strong>the</strong> fruits <strong>the</strong>y eat, <strong>and</strong> <strong>the</strong> same competition
may occur in <strong>the</strong> rainforests <strong>of</strong> Cape York Peninsula.
More than any o<strong>the</strong>r animal, pigs have a digestive system like that <strong>of</strong> humans, <strong>and</strong>
<strong>the</strong>y feed on many indigenous food plants, including bulgaru, native potatoes
(Ipomoea calobra), p<strong>and</strong>anus fruits <strong>and</strong> seeds, Leichardt tree fruit, sacred lotus <strong>and</strong>
lillypillies (Syzygium species) (Anonymous 2003).
Disease Spread
In north Queensl<strong>and</strong> (<strong>and</strong> Hawaii) pigs are strongly implicated in <strong>the</strong> spread <strong>of</strong> <strong>the</strong>
root-rot fungus (Phytophthora cinnamomi), a soil borne disease that kills trees <strong>and</strong>
shrubs (Choquenot etal. 1995). This disease is highly destructive in many parts <strong>of</strong>
coastal Australia outside <strong>the</strong> Rangel<strong>and</strong>s. Within <strong>the</strong> Rangel<strong>and</strong>s it is most likely to
prove damaging if it reaches <strong>the</strong> rainforests on Cape York Peninsula. Pigs are active
in <strong>the</strong>se forests. It causes tree deaths in rainforests fur<strong>the</strong>r south. Dieback caused by
<strong>the</strong> root-rot fungus (Phytophthora cinnamomi) has been listed by <strong>the</strong> federal
government as a Key Threatening Process.
Pigs also carry human <strong>and</strong> livestock diseases such as tuberculosis, leptospirosis, swine
brucellosis, Ross River <strong>and</strong> dengue. They are also thought to spread <strong>the</strong> cocoons <strong>of</strong>
<strong>the</strong> Amazonian earthworm (Pontoscolex corethrurus), which is common in north
Queensl<strong>and</strong> rainforests <strong>and</strong> compacts soild resulting in <strong>the</strong> degradation <strong>of</strong> native flora
(Low 1999).
Spread <strong>of</strong> weeds
Pigs disperse <strong>the</strong> seeds <strong>of</strong> some major weeds, including pond apple (Annona glabra),
mimosa (Mimosa Pigra) (A. Ferguson pers. comm.), <strong>and</strong> mesquite (Prosopis species),
three <strong>of</strong> Australia’s 20 worst weeds. Pigs contribute to weed invasion both by
spreading seeds directly (by eating weed fruits <strong>and</strong> pods <strong>and</strong> excreting <strong>the</strong> seeds) <strong>and</strong>
by disturbing large areas <strong>of</strong> soil when <strong>the</strong>y feed. Weeds preferentially colonise
disturbed ground. On Cape York Peninsula, ‘extensive trampling, digging <strong>of</strong>
vegetation <strong>and</strong> ground by pigs <strong>and</strong> a succeeding invasion <strong>of</strong> weeds were observed
throughout <strong>the</strong> region’ (Anonymous 2003).
On <strong>the</strong> Finnis River Basin in <strong>the</strong> Nor<strong>the</strong>rn Territory pigs are identified as an
increasing problem because <strong>of</strong> <strong>the</strong>ir role in spreading mimosa (Nor<strong>the</strong>rn L<strong>and</strong> Council
2004):
‘They ‘cultivate’ large areas <strong>of</strong> <strong>the</strong> floodplain in search <strong>of</strong> food <strong>and</strong> this
provides ideal nursery for mimosa seedlings to establish. Pigs shelter in
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