Predation, habitat degradation, competition and disease transmission by feral pigs (Sus scrofa) - key threatening process listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list Predation, habitat degradation, competition and disease transmission by Feral Pigs, Sus scrofa Linnaeus 1758, as a KEY THREATENING PROCESS in Schedule 3 of the Act. Listing of key threatening processes is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. Feral Pigs, Sus scrofa Linnaeus 1758, are descended from domestic stock introduced to Australia by European settlers, and possibly from introductions to northern Australia from Timor and New Guinea (Choquenot  et al. 1996; Pavlov 2000). Feral Pigs are found across continental Australia with the highest densities in NSW, Qld and through northern Australia to the Kimberley region. In 2002, Feral Pigs were estimated to inhabit 61% of the area of NSW and the ACT (West and Saunders 2003). 'Predation, habitat degradation, competition and disease transmission by Feral Pigs' is currently listed as a key threatening process under the Commonwealth  Environment Protection and Biodiversity Conservation Act 1999.

2. Feral Pigs are opportunistic omnivores (Pavlov 2000). They feed predominantly on grasses, however, bulbs, tubers, roots, seeds, fruit, fungal fruit-bodies (sporocarps), carrion, and vertebrate and invertebrate prey are all consumed when available.

3. Feral Pigs use a wide range of habitat types, however, the species' distribution is governed largely by its requirement for shade and access to daily water (Choquenot et al. 1996) e.g. in Nocoleche Nature Reserve, north-west NSW, Feral Pigs were restricted to shady habitats during hot weather, and in cooler weather were distributed according to the availability of food (Dexter 1998). Throughout its range, the species has shown a preference for riparian and swampy habitats (Caley 1997; Mitchell and Mayer 1997; Dexter 1998) as well as dense vegetation types such as wet sclerophyll forest (Laurance and Harrington 1997) and forested gullies (Saunders and Kay 1991).

4. Feral Pigs have a high reproductive potential (Choquenot et al. 1996). Piglets attain sexual maturity at approximately seven months (Pavlov 2000) and females may produce two litters of six piglets every 12 to 15 months (Menkhorst 1995). The species can reproduce rapidly in response to favourable environmental conditions e.g. at the Macquarie Marshes, central-west NSW, the maximum annual increase in the Feral Pig population was estimated to be nearly 300%, despite a high rate of mortality from shooting (Giles 1976). A majority of Rural Lands Protection Boards believe that feral pig populations were increasing in their area (S Orr pers. comm. 2004).

5. Feral Pigs present a significant threat to native species and ecological communities as a result of their behaviour and feeding habits. Feral Pig wallowing and rooting causes direct disturbance to habitats (Hone 2002) and may increase erosion and reduce water quality in streams and pools (Department of Environment and Heritage (DEH) 2003a) e.g. wallowing and rooting by Feral Pigs has been identified as a threat to the vulnerable Northern Corroboree Frog, Pseudophryne pengilleyi (ACT Government 1997). Further, disturbance of habitats by Feral Pigs may also facilitate the invasion and spread of weeds and thus affect the composition of plant communities (DEH 2003b). A survey of vertebrate pest species in NSW National Parks and Wildlife Service estate found that Feral Pigs were known have negative impacts in at least 33 of 100 reserves from which they were reported (Harden 1997). These 33 reserves occur throughout the state and include Narran Lake Nature Reserve and Goulburn River National Park, Kosciuszko and Budawang National Parks, Werrikimbe and Boonoo Boonoo National Parks, and Kanangra-Boyd National Park.

6. Feral Pigs are active predators of native birds, reptiles, (including their eggs), frogs and soil invertebrates such as earthworms as well as the underground storage organs of plants and the fruiting bodies of fungi. Predation by the Feral Pig was implicated as a major cause of decline in several bird species e.g. Hutton's Shearwater, Puffinus huttoni, in New Zealand (Cuthbert 2002), the endangered Lord Howe Woodhen,  Gallirallus sylvestris, and the vulnerable Providence Petrel,  Pterodroma solandri also on Lord Howe Island (DEH 2003a) although Feral Pigs are now eradicated from the island. Further, direct predation by Feral Pigs may have contributed to declines in populations of some frog species (Richards  et al. 1993).

7. Feral Pigs present a threat to native fauna through competition for food resources. Competition between Feral Pigs and the Endangered Brolga, Grus rubicunda, for bulbs and tubers has been observed in northern Australia (Tisdell 1984), and such competition is likely to occur within the range of the Brolga in NSW. Consumption of fungal fruit-bodies by Feral Pigs is likely to conflict with the dietary preferences of several threatened small mammal species (Laurance and Harrington 1997; Pavlov 2000), including the Southern Brown Bandicoot,  Isoodon obesulus obesulus, Rufous Bettong,  Aepyprymnus rufescens, and Long-nosed Potoroo,  Potorous tridactylus. Such competition is a particular threat to the endangered Long-footed Potoroo,  Potorous longipes, the diet of which is more than 80% fungal fruit-bodies (Seebeck 2000).

8. Feral Pigs have been implicated as potential vectors of disease. In particular, Feral Pigs may be responsible for spreading Phytophthora cinnamoni, a root-rot fungus responsible for die-back in native vegetation (DEH 2003b). There is evidence that Feral Pigs can carry the fungus on their hooves (Kliejunas and Ko 1976), and that the spread of the fungus is associated with soil disturbance and reduction of litter cover by pigs (Brown 1976). Further, chewing and other damage to tree trunks may facilitate infection of vegetation by the fungus and other diseases.

9. The following threatened species and ecological communities known or likely to be threatened by Feral Pigs include:

10. In view of the above the Scientific Committee is of the opinion that Predation, habitat degradation, competition and disease transmission by Feral Pigs, Sus scrofa Linnaeus 1758, adversely affects more than two threatened species, populations or ecological communities, or could cause species, populations or ecological communities that are not threatened to become threatened.

Associate Professor Paul Adam
Chairperson
Scientific Committee

Proposed Gazettal date: 27/08/04
Exhibition period: 27/08/04 - 08/10/04

References 

ACT Government (1997) 'Corroboree Frog (Pseudophryne corroboree): a vulnerable species.' Action Plan No. 6, Environment ACT, Canberra.

Brown BN (1976) Phytophthora cinnamoni associated with patch death in tropical rainforests in Queensland.  Australian Plant Pathology Society Newsletter 5, 1-4.

Caley P (1997) Movements, activity patterns and habitat use of Feral Pigs (Sus scrofa) in a tropical habitat.  Wildlife Research 24, 77-87.

Choquenot D, McIlroy J, Korn T (1996) 'Managing vertebrate pests: Feral Pigs.' (Australian Government Publishing Service: Canberra).

Cuthbert RR (2002) The role of introduced mammals and inverse density-dependent predation in the conservation of Hutton's shearwater. Biological Conservation 108, 69-78.

Dexter N (1998) The influence of pasture distribution and temperature on habitat selection by feral pigs in a semi-arid environment. Wildlife Research 25, 547-559.

Department of Environment and Heritage (2003a) Feral animals: Feral Pigs - Sus scrofa. Retrieved 23 September, 2003.

Department of the Environment and Heritage (2003b) 'Draft threat abatement plan for predation, habitat degradation, competition and disease transmission by Feral Pigs.' Department of Environment and Heritage, Canberra.

Giles JR (1976) Feral pigs and agriculture. In 'Agriculture, forestry and wildlife: conflict or coexistence? Proceedings of a workshop held at the University of New England, Armidale, New South Wales'. pp. 125-128.

Harden J (1997) 'A survey of vertebrate pests in the service estate.' NSW National Parks and Wildlife Service, Armidale, NSW.

Hone J (2002) Feral pigs in Namadgi National Park, Australia: dynamics, impacts and management. Biological Conservation 105, 231-242.

Kliejunas JT, Ko WH (1976) Dispersal of Phytophthora cinnamoni on the island of Hawaii.  Phytopathology 66, 457-460.

Laurance WF, Harrington, GN (1997) Ecological associations of feeding sites of feral pigs in the Queensland wet tropics. Wildlife Research 24, 579-590.

Menkhorst PW (1995) Pig, Sus scrofa Linnaeus, 1758. In 'Mammals of Victoria: distribution, ecology and conservation'. (Ed. PW Menkhorst) pp. 274-275. (Oxford University Press: Melbourne).

Mitchell J, Mayer R (1997) Diggings by Feral Pigs within the Wet Tropics World Heritage Area of north Queensland. Wildlife Research 24, 591-601.

Pavlov PM (2000) Pig, Sus scrofa Linnaeus, 1758. In 'The Mammals of Australia'. (Ed. R Strahan) pp. 715-717. (Reed Books: Sydney).

Richards SJ, McDonald, Alford RA (1993) Declines in populations of Australia's endemic tropical frogs. Pacific Conservation Biology 1, 66-77.

Saunders G, Kay B (1991) Movements of feral pigs (Sus scrofa) at Sunny Corner, New South Wales.  Wildlife Research 18, 49-61.

Seebeck JH (2000) Long-footed Potoroo Potorous longipes Seebeck and Johnston, 1980. In 'The mammals of Australia'. (Ed. R Strahan) pp. 298-299. (Reed Books: Sydney).

Tisdell CA (1984) Feral pigs threaten native wildlife in Australia. Tigerpaper 11, 13-17.

West P, Saunders G (2003) 'Pest animal survey 2002: an analysis of pest animal distribution and abundance across NSW and the ACT.' NSW Agriculture, Orange.