Indicator: Pest Animals
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Summary of results
Pest animals remain a potentially significant threat to biodiversity in the ACT despite measures for their control and management. The ACT Vertebrate Pest Management Strategy (2002) forms the basis for vertebrate pest control in the ACT.
Fox and rabbit numbers appear to be toward the lower end of their historical range; deer, pigs and goats are present in low numbers; small numbers of horses have been active on the boundary of Namadgi National Park; wild dogs have required ongoing control; and there are new populations of the Oriental Weatherloach.
The European Wasp and Common Myna have become more firmly established. An innovative trapping trial is underway for the latter. In response to increased road collisions with kangaroos, the Government initiated a driver awareness campaign (‘Give Kangaroos a Brake’) in 2002.
What the results tell us about the ACT
Pest animals remain a significant threat to the ACT ecosystem despite measures for their control and management. The South East Highlands Interim Biogeographic Regionalisation for Australia (IBRA) region, of which the ACT is a part, has the highest number of non-indigenous invasive terrestrial species, based on a list of about 30 species considered to have a major impact in Australia (Williams et al. 2001).
Pest animals established in the ACT include mammals (feral cats, feral goats, feral pigs, foxes, rabbits, wild dogs), fish (Carp, Oriental Weatherloach, Redfin) and birds (Common Starling, Common Myna, Common Blackbird). Feral horses recently re-entered Namadgi National Park from Kosciuszko National Park where the population was estimated at 3000 before the January 2003 bushfires (NSW NPWS 2003). Deer are present in low numbers.
In the reporting period, there is evidence that the European Wasp (Vespula germanica) and Common Myna have become firmly established and widespread in the ACT while the Eastern Grey Kangaroo (Macropus giganteus) has continued to require management.
Pest management strategy finalised
Since the previous reporting period the ACT Government has finalised the ACT Vertebrate Pest Management Strategy (ACT Government 2002) that forms the basis for vertebrate pest control in the ACT. The Strategy, with the full list of pest species, is available from
Environment ACT has prepared a control program for 2002–03 (Environment ACT 2002) based on the principles in the Strategy. In 2003–04 the ACT Parks and Conservation Service is conducting a survey of major pest animal distribution, involving parks staff and some rural leaseholders. A pest animal management plan for land west of the Murrumbidgee River in the ACT is also being developed as part of the vertebrate pest control program.
Species of concern
The Strategy contains a list of key vertebrate pests, their environmental and rural production impacts, management issues, current management practices and the outlook for their management. Select species for which there has been a change in information are listed at the end of this page.
Other potential pests in the ACT include the Red Fire Ant Solenopsis invicta (currently the subject of an intense eradication program in southeast Queensland) and the Red-eared Slider Turtle, Trachemys scripta elegans (an exotic aquarium species now present in two New South Wales coastal waterways and capable of survival in cold waters).
Other species of concern
The European Wasp (Vespula germanica) is favoured by relatively mild Australian winters and is expanding its range. it is a threat to biodiversity and public health. Low rainfall in the ACT in the reporting period (especially 2002–03) seems to have favoured maintenance of European Wasp nests and the numbers of wasps throughout urban ACT. Calls to the CSIRO entomological hotline,and the number of nests destroyed by Canberra Urban Parks and Places (Table 1) generally support this observation.
Source: CSIRO Entomology and Canberra Urban Parks and Places
In 2002–03, the ACT Beekeeper’s Association removed more than 100 feral bee swarms, such as European Honeybee (Apis mellifera), about 30 of which were on urban parkland.
Semi-permanent urban populations of the Pied Currawong (Strepera graculina) have increased substantially over the past three decades (Major 2003). Populations may have increased during the reporting period, but further research is needed to tell whether this is a prime factor in the decline of small bush birds. A large-scale nest predation experiment, conducted Australia-wide by Major et al. (1996), found evidence to suggest Pied Currawongs were a major threat to small birds in urban environments. Another study (Fulton and Ford 2001) considered this species to be a significant predator in rural woodland fragments. A pair of Currawongs may kill 40 broods of small birds to raise a brood of their own (Major 2003).
However, other studies concluded that Currawong predation is highest on common (introduced and native) species (Bayly & Blumstein 2001), but it fails to show any population decline in the prey species. For example, the Superb Fairy-Wren (Malurus cyaneus) that experiences a high level of nest predation by Currawongs in the ACT, has increased in population for more than a decade (COG 2002). Canberra Ornithologists Guild (COG) records show that the measure of abundance for Pied Currawongs from reporting records has changed little in 21 years of surveys (COG 2002).
The Common Myna (Acridotheres tristis) has shown a dramatic increase in abundance and extent in the ACT since the late 1980s. The COG annual bird report for 2001–02 records the myna as Canberra’s fourth most abundant Garden Bird Survey species recorded from 96.6% of sites (COG 2002).
Mynas are considered a biodiversity threat primarily because they compete aggressively with native birds and mammals for nest hollows. Old trees with hollows are a key habitat resource now being lost at a rate greater than replacement.
Dr Chris Tidemann of the Australian National University conducted a myna control trial in August 2001 supported by funding of $12,000 by Environment ACT. Four traps were constructed and operated in Canberra backyards during 2001–02 (Tidemann 2003). The traps used decoy birds and featured a selective and humane multi-catch trap with euthanasia of captured birds by carbon dioxide.
More than 300 mynas were caught over 18 months at each of two sites suggesting that safe, selective and humane removal of mynas is possible. The traps are now in commercial production. Planning is underway, in collaboration with Environment ACT and the Canberra Ornithologists Group, for a larger trial to answer the questions of whether mynas can be cost-effectively controlled, and the number of traps needed to achieve a particular population reduction (Tidemann 2003).
The localised and social nature of myna populations means large numbers may be trapped. Given that mynas are relatively slow invaders and breeders, population control efforts could be worthwhile and economic.
Strong support exists within the ACT community for control of mynas, even though the specific biodiversity benefits and effectiveness of a control program may be the subject of debate (Braysher 2002; Tidemann 2002).
Eastern Grey Kangaroo
Eastern Grey Kangaroo (Macropus giganteus) densities in isolated grassland areas in the ACT are the highest reported in Australia. High density kangaroo populations may be linked to soil erosion, but investigations have not yet identified any significant adverse impacts on biodiversity. Kangaroos may also be considered a problem species because they compete with grazing, and can be involved in road collisions. The ACT Parks and Conservation Service keeps records of reported road kills of kangaroos in the urban areas of the ACT (see Table 2). Virtually all road kills are Eastern Grey Kangaroos and a few Wallaroos (Macropus robustus). A substantial number of road kills are unreported.
|Year||Wounded and euthenased||Killed in collision||Total (change from previous year)||Calls regarding dead or injured kangaroos|
|2000||258||384||642 (+ 42%)||905|
|2001||276||528||804 (+ 25%)||1100|
|2002||470||662||1132 (+ 41%)||1522|
|2003 (Jan–June)||441||501||942 (n/a)||1071|
Source: Data from ACT Parks and Conservation Service
The substantial increase in kangaroo mortality in 2002 is attributed to drought conditions and bushfires resulting in more kangaroos grazing by roadsides. In August 2002 the ACT Government (Environment ACT) introduced the ‘Give Kangaroos a Brake’ campaign, warning of the danger and advising drivers to slow down in high-risk zones marked by warning signs. This campaign has continued in 2003 with media publicity and ongoing financial support from the NRMA.
ACT rural producers also shoot thousands of Eastern Grey Kangaroos each year during a shooting season determined on animal welfare grounds, and according to limits determined by a formula based on the difference between rated stock carrying capacity and estimates of kangaroo density.
Data sources and references
ACT Government 1998 The ACT Nature Conservation Strategy (Environment ACT, Canberra).
ACT Government 2002 ACT Vertebrate Pest Management Strategy (Environment ACT, Canberra).
ACT Government 2003 Woodlands for Wildlife: Draft ACT Lowland Woodland Conservation Strategy. Action Plan No. 27 (Environment ACT, Canberra).
Bayly, KL & Blumstein, DT 2001, ‘Pied Currawongs and the decline of native birds’, Emu 101: 199–204.
Braysher, M 2002 ‘Should we, or can we, control myna incursion?’, The Canberra Times 5 September 2002, p. 18.
Canberra Ornithologists Group 2002, ‘Annual Bird Report: 1 July 2001 to 30 June 2002’, Canberra Bird Notes 27 (4): 145–202.
Environment Australia 2000, Revision of the Interim Biogeographic Regionalisation of Australia (IBRA) and the Development of Version 5.1. Summary Report, Department of Environment and Heritage, Canberra.
Environment ACT 2002, ACT Vertebrate Pests Control Program 2002–03 Unpublished, Environment ACT, Canberra.
Ford, HA, Barrett, GW, Saunders, DA & Recher, HF 2001, ‘Why have birds in the woodlands of southern Australia declined?’, Biological conservation 97: 71–88.
Fulton, GR & Ford, HA 2001, ‘The Pied Currawong’s role in avian nest predation: a predator removal experiment’, Pacific Conservation Biology 7: 154–60.
Garnett, ST & Crowley, GM 2000, The Action Plan for Australian Birds 2000, Environment Australia, Canberra.
Gullan, PJ 1999, ‘Information to assist consideration of the potential conservation threat posed by the spread of the European wasp, Vespula germanica and the potential introduction of the English wasp, V. vulgaris in the ACT region’, prepared for the ACT Flora and Fauna Committee, June 1999.
Major, RE, Gowing, G & Kendal, CE 1996, ‘Nest predation in Australian urban environments and the role of the pied currawong, Strepera graculina’, Australian Journal of Ecology 21: 399–409.
Major, R 2003, ‘Urban Currawongs’, Nature Australia, 27 (9) Winter: 52–9.
New South Wales National Parks and Wildlife Service 2003, Wild Horse Management Plan for the alpine area of Kosciuszko National Park, NSW NPWS, Jindabyne.
Pell, AS & Tidemann, CR 1997, ‘The ecology of the common myna (Acridotheres tristis) in urban nature reserves in the Australian Capital Territory’, Emu 97: 141–9.
Pullen, K 2001, ‘The European Wasp’, Bogong, 22 (2): 13–15.
Taylor, McC & Canberra Ornithologists Group 1992, Birds of the Australian Capital Territory – an Atlas, COG and the National Capital Planning Authority, Canberra.
Tidemann, CR 2002, ‘Myna not a minor problem – solution required’, The Canberra Times, 26 September 2002, p.15.
Tidemann, CR 2003, Mitigation of the impact of mynas on biodiversity and public amenity, unpublished report on Minimising Mynas Project Phase 1 (ENV 99: 019), Australian National University, Canberra.
Williams, J, Read, C, Norton, A, Dovers, S, Burgman, M, Proctor, W & Anderson, H 2001 Biodiversity, Australia State of the Environment Report 2001 (Theme Report), CSIRO Publishing on behalf of the Department and Environment and Heritage, Canberra.
Updated information on particular pest animals listed in the ACT Vertebrate Pest Management Strategy during 2000–03
|Condition||Numbers considered moderate. Fox numbers appear to have remained stable despite drought conditions and fire impacts. Further analysis is required of monitoring undertaken to confirm whether this is actually the case. This is proposed for 2003–04.|
|Impacts||Decline in rabbit numbers may be resulting in increased predation on native species, but no documented evidence.
There is evidence of fox presence in areas burnt in January 2003 and this may be significant predation pressure on animals that survived the fires. As cover re-establishes after fires this issue will be of less concern
|Response||Approximately 100 fox control programs have been conducted since 2000, of which over 85 were directly for rural production, not biodiversity management. A long-term fox baiting program continues in the Mt Clear and Boboyan valleys within Namadgi National Park. Evidence is emerging that in areas where active fox control is undertaken that rabbit numbers are also declining: the opposite of what may be expected in such circumstances. Theory proposed for this is that greater interaction between rabbits infected with Rabbit Haemorrhagic Disease occurs in the absence of foxes.|
|Status and outlook||The fox continues to be considered a threat to biodiversity. However, the impact of foxes on populations of native species in the ACT remains unclear. Further examination of current fox control programs aimed at biodiversity protection will be undertaken over the next few years.
Baiting remains the only viable control method available at present to reduce the adverse impact of foxes.
Foxes within the urban area remain problematic in the absence of viable control strategies.
|Condition||From first record in Lake Burley Griffin in 1980 has become widely established in ACT streams including Cotter River above Cotter Reservoir. Main reason for spread is that species is harvested and used illegally as a bait fish.|
|Impacts||Oriental Weatherloach has significant dietary overlap with native Mountain Galaxias Galaxias olidus.|
|Response||The ACT Fisheries Act 2000 bans the use of live fish as bait. This is included in information provided to fishers on recreational fishing in the ACT.|
|Status and outlook||New populations have established in the Queanbeyan, Molonglo and lower Gudgenby rivers. No means to control spread of species other than angler education evident at present.|
|Condition||Population low at present, anecdotally much reduced immediately following the January 2003 bushfires, but recent reports suggest populations may once again be increasing.|
|Impacts||Impact is probably very low at present. However, deer are selective browsers that can have an impact on native plant regeneration if populations increase.|
|Response||Monitoring – deer sightings are reported to the Vertebrate Pest Control Officer.|
|Status and outlook:||Monitoring, recording of sightings, keep under review need for a control program.|
|Condition||Numbers appear stable at lower end of historical range, or to have slightly increased in most areas being monitored. However, monitoring counts have yet to be fully analysed to confirm this.
Reports from the ACT and adjacent NSW suggest that suitable climatic conditions for the spread of Rabbit Haemorrhagic Disease (RHD) did not occur until late autumn/winter but did have an effect on rabbit numbers.
|Impacts||A potential impact of increased rabbit numbers may be to suppress regeneration of native plants following the fires in January 2003. This will be difficult to monitor across the ACT, particularly as drought conditions are also a factor influencing regeneration. General observations and spotlighting figures suggest that the January 2003 fires did not significantly reduce numbers.
As reported for foxes, evidence is emerging that increased fox control may contribute to increased effectiveness of RHD.
|Response||Considerable rabbit control effort was undertaken in autumn 2003 on both rural properties and reserve areas.
The removal/suppression of surface vegetation due to fire and drought conditions has provided greater opportunity to locate warrens, and has meant that surface living rabbits are more conspicuous.
Extensive warren ripping and some blasting has occurred at Tidbinbilla Nature Reserve, Namadgi National Park and in parts of Canberra Nature Park, with follow up poison programs.
Rabbit impacts on revegetation areas will be monitored and control action undertaken as required.
A number of reports of increased rabbit activity have been received within the urban area.
|Condition||Populations of feral pigs remain comparatively low across most of the ACT.|
|Impacts||Feral pigs are possibly not exerting significant pressure on biodiversity values at present due to low numbers. Local impacts may still be significant. Migration from areas not subject to control is of potential concern due to the extreme sensitivity of many vegetation communities severely affected by fire – in particular bogs and riparian zones.|
|Response||Annual pig control program 2002–03 was recently completed within Namadgi National Park. The number of poisoned baits taken this year was significantly less than in previous years. It is possible that pig numbers were reduced as a result of January 2003 fire, fire fighting activity on trails scared pigs away from bait stations, more attractive food sources were available in regenerating vegetation.
Identified ‘at risk’ vegetation communities will be monitored throughout the year for presence of pigs.
|Status and outlook||Pig control is an ongoing task. The objective of the 2002–03 control program is to maintain feral pig populations at current low levels. Monitoring of ‘at risk’ plant communities will be undertaken and specific control action initiated if required.
Reduction in vegetation cover after the January 2003 bushfires may make pigs more vulnerable to predation by wild dogs.
|Condition||Reports of small numbers of feral horses entering Namadgi National Park from adjacent areas of NSW. In 2002 Kosciuszko National Park was estimated to contain approximately 3000 feral horses, with 1600 of these north of the Alpine Way. These numbers have been reduced by the bushfires of January 2003 (possibly by one-third), however, numbers in the less intensely burned areas in Northern Kosciuszko National Park were not significantly reduced and remain a threat to the ACT.|
|Impacts||Previous experience with horses in Namadgi National Park has demonstrated that even relatively small populations of horses can have significant detrimental impacts on sensitive vegetation communities and water quality.
Severe impacts of fires in many areas known to be preferred horse habitat have increased the potential for damage.
Feral Horses have been confirmed as being present within the Park.
|Response||Horse activity within the Namadgi National Park is being monitored. A draft management strategy has been prepared in consultation with stakeholders and is awaiting final approval for actions to commence. Fencing of likely entry points has commenced.
Lethal and non-lethal removal options have been included within the plan, recognising that lethal control of horses is an extremely contentious issue. Options for removal of captured horses are currently being pursued.
|Status and outlook||Removal of horses is an extremely sensitive issue.
Objective of control program to prevent re-invasion of upper Cotter area. Ongoing monitoring.
Fire has removed natural barriers for migration into Namadgi National Park from NSW.
The arrival of Feral horses back into Namadgi National Park will require a long term commitment to control. Close liaison and cooperation with NSW authorities is occurring to ensure a coordinated approach.
|Condition||Currently, goat numbers are reported to be low within the ACT.
Failure of feral goat populations to recover from shooting programs in the 1970s and 1980s is considered likely to be due to suppression by dingoes/wild dogs.
|Impacts||Probably minimal impact at present. However previous experience with higher population levels demonstrates they have the potential to significantly impact on biodiversity values if numbers are allowed to increase. Selective browsing by goats on regenerating vegetation has the ability to alter plant communities. High goat densities may also contribute to soil erosion of areas left bare after the fires of January 2003.|
|Response||Loss of vegetation post-fire has allowed more effective detection of goats and some have been removed. Radio collars have been fitted to a small number of Judas goats to allow tracking of their distribution within Namadgi National Park and adjacent areas.
Few sightings of goats are currently being reported. immediately after the January 2003 bushfires.
|Status and outlook||Objective of control program is to maintain goats at current low level. Environment ACT is currently waiting on final tracking results for goats and will evaluate need for control based on environmental impacts. Local eradication of goats is possible, but it is difficult and expensive to obtain complete removal. Populations re-establish over time so need for ongoing program.|
|Condition||Local populations include a few genetically pure dingoes with a majority of hybrids between dingoes and other dogs. Irrespective of genetics, these populations have a dual role. They are serious pests on the edge of sheep farming areas, but away from agricultural areas are valued for suppressing pests such as pigs, goats and rabbits and may help maintain biodiversity of their native prey. The hybrid animals behave like dingoes (howling not barking and hunting large prey in packs), are the same size and shape, and have the same ecological function, but they do not look like dingoes.
Visible signs of dogs are more obvious at the end of the reporting period due to the loss of screen vegetation in the January 2003 bushfires and footprints left in recently graded trails.
Control program focussed to prevention of stock losses.
|Impacts||Biodiversity relationships unknown. Most focus is on rural production impacts. One biodiversity impact is the loss of genetic purity of the dingo due to hybridisation. The ‘park edge buffer zone strategy’ used to reduce stock losses may also reduce the inflow of dog genes.
Management zones for wild dog control have been identified to provide for protection to sheep production, whilst also allowing for ecological function.
Reported sheep losses attributed to wild dogs was at the lower end of the historical average in 2003.
|Response||Extensive trapping and baiting programs on rural interface areas, with some opportunistic control undertaken within park areas for a short period after fires of January 2003.
A significant increase in resources for the wild dog control program over the past three years.
Extensive trapping and baiting programs on rural interface areas.
A significant increase in resources for the wild dog control program over the past three years.
Baiting has to consider non-target species e.g. all forested areas are potential habitat of Spotted-tailed Quolls (Dasyurus maculatus) and quoll scats have been found in all surveys following the January 2003 fire. Management is very likely to benefit from better knowledge of dingo (dog) ecology, and quoll ecology.
|Status and outlook||Ongoing issues of wild dog versus dingo. Proposal for a national vertebrate pest strategy may assist in shaping objectives regarding wild dogs and dingoes (e.g. by defining zones where priority is given to maintaining genetic integrity of dingoes).
Ongoing management of a buffer zone is important to protection of sheep grazing and biodiversity conservation. Killing individual dogs in other areas where stable packs may exist is thought likely to disrupt the social structure and risk a counter-productive increase in surplus killing – requiring land managers to undergo sustained control programs (that is, short term or ad hoc programs may be of little value or even counter-productive).