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Report for the australian government department of the environment, water, heritage and the arts

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February 2010


Prepared by:

Professor Christopher R. Dickman1

Doctor Elizabeth Denny1

Tony Buckmaster1
1Institute of Wildlife Research

School of Biological Sciences

Heydon-Laurence Building A08

University of Sydney

Sydney 2006


This report should be cited as: Dickman, C.R. Denny, E. and Buckmaster, T. 2010 Identification of sites of high conservation priority impacted by feral cats. Report for the Australian Government Department of the Environment, Water, Heritage and the Arts. Canberra, Australia.

© Commonwealth of Australia 2010

This work is copyright. You may download, display, print and reproduce material in unaltered form only (retaining this notice) for your personal, non-commercial use or use within your organisation. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. Requests and inquiries concerning reproduction and rights should be addressed to Commonwealth Copyright Administration, Attorney General’s Department, Robert Garran Offices, National Circuit, Barton ACT 2600 or posted at


The views and opinions expressed in this report reflect those of the authors and do not necessarily reflect those of the Australian Government or the Minister for Environment Protection, Heritage and the Arts.

The contents of this document have been complied using a range of source materials and is valid as at February 2010. While reasonable efforts have been made to ensure that the contents of this publication are factually correct, the Commonwealth does not accept responsibility for the accuracy or completeness of the contents, and shall not be liable for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of this publication.

Table of Contents


Scope of report 1

Background 2

Limitations 4
Threatened species potentially impacted by feral cats 5

Data acquisition 9

Questionnaire 9

Personal contacts 10

Literature search 10

Mainland bioregions and sites 10

Island bioregions and sites 10

Prioritisation of sites 11

Criteria for interactive decision-making tree 11

Cat presence/absence 11

Likelihood of invasion or re-invasion 11

Threatened species 11

Vulnerability of threatened species to cat predation 12

Status of species identified at each site 12

Multiple-use interactive decision-making tree 14

Data acquisition 15

Questionnaire responses 15

IBRA regions 15

Prioritisation of regions and sites at risk of impact from feral cats 15

IBRA regions 15

Specific sites 18

Data deficient sites 24

Specific sites where feral cats do not occur 24

Caveats and interpretations of the prioritisation analyses 27

Prioritising bioregions versus specific sites 30

The bioregional approach 30

The site-level approach 31

Synthesis and suggestions for prioritisation 33

Options for eradication of feral cats 33

Shooting 34

Poisoning 34

Trapping 36

Exclusion fencing 36

Public perceptions 36

Strategic pest management 37

Assessing the impact of feral cats 38

Monitoring feral cats 38

Cat management and regulatory controls 39

Control programs at identified sites 40

Regional cat eradication and control programs 41

Control and monitoring options 42

Conclusions 43

Recommendations for feral cat control programs 44


Appendix A 60

Appendix B1 61

Appendix B2 62

Appendix C 63

List of Tables
Table 1 Threatened species and critical habitats that may be

adversely affected by feral cats 5

Table 2 Levels of decision-making used in the construction

of a multiple-use decision-making tree 12

Table 3 Prioritised scores for IBRA regions and number of TAP (2008) -listed species in each region 15
Table 4 Prioritised mainland and island sites, the states and the scores calculated from the decision-making tree 18
Table 5 Prioritised data deficient mainland and island sites, the states and scores calculated from the decision -making tree with the score for cat management omitted from the calculations 24
Table 6 Prioritised mainland and island sites that are free of cats but may potentially face invasion or re-invasion 25
Table 7 Feral cat control programs at sites identified where feral cats pose or potentially pose a significant risk to native species 40
List of Figures
Fig 1 IBRA regions with prioritisation scores 23
Fig 2 Prioritised sites including scores 26


Feral cats (Felis catus) have been recorded throughout the Australian mainland and on many offshore islands. Predation by feral cats has been implicated, together with other factors, in the population declines of many species of native vertebrates. Some of these declines have resulted in the shifting of species’ conservation status to a more endangered level, with several native species having become extinct. Predation by feral cats is classified as a key threatening process by the Australian Government under the Environment Protection and Biodiversity Conservation Act 1999.

The cryptic nature of the cat, its exploitation of both modified and unmodified habitats, its status as both a pest and a pet species, and the abundance of introduced prey species and supplemental food sources throughout its range, all contribute to the many acknowledged problems associated with the control or eradication of feral cats in Australia.

In the absence of a single, robust way to measure cat densities and the known difficulties associated with assessing cat impacts at the species level, indirect methods are required to prioritise sites for the implementation of cat control programs.

This report uses an interactive decision-making tree based on characteristics of prey species to provide a relative measure of probable cat impacts between sites on the Australian mainland and offshore islands. The decision-making tree provides a single score for geographical (IBRA) regions, specific mainland sites and offshore islands that may be used comparatively for the allocation of resources for cat control programs. Although the scores in this report are based only on those species listed in the Australian Government’s Threat Abatement Plan for Predation by Feral Cats (2008), comparative scores can be calculated and allocated for sites that support any species at risk of predation by feral cats and classified as threatened, endangered, or vulnerable at the national, state or local level. Indeed, the decision-making tree also allows non-threatened species to be assessed for their risk of predation from cats, should the need arise to do so.

The interactive decision-making tree provided comparative scores for the potential impact of cats in each IBRA region of Australia. These scores varied from a high of 328 for the South Eastern Highlands IBRA region of eastern Australia, to a low of 24 for the Gawler IBRA region of South Australia and for three other IBRA regions located wholly or largely in Western Australia. However, there were also 9 IBRA regions with no extant TAP-listed species; these consequently received no scores. The decision-making tree also provided comparative scores for the impact of feral cats in specific sites throughout the mainland and on offshore islands. These scores, based on data provided by land managers or available in the literature, varied from highs of 117 for the Diamantina National Park in Queensland and 108 for the East Gippsland area in Victoria, to a low of 10 for Dirk Hartog Island off the Western Australian coast. Further scores were calculated for sites at which cat control is uncertain (‘data deficient’) and from which cats have been eradicated or never recorded to identify sites that could be potentially impacted by feral cats in future. These scores varied from a high of 201 for sub-Antarctic Macquarie Island to a low of 9 for Boondelbah Island off the coast of New South Wales.

We conclude that feral cat control on the Australian mainland is a long-term, multi-faceted, labour- and resource-intensive venture requiring site-specific control methods that provide systematic and regular downward pressure on feral cat populations. An effective program of management should also include concurrent control of populations of both stray and owned domestic cats. We conclude further that greater success in cat control programs will be achieved by targeting specific sites using site-specific control methods. Human activities such as urban and rural development, agriculture and habitat modification favour the establishment and maintenance of feral cats. We recommend that a ‘nil tenure’ approach to cat control, with management activities encompassing public- and privately-owned reserved land as well as adjacent urban, rural and semi-rural developments, is necessary to reduce the feral cat population on the Australian mainland and offshore islands. In the absence of a sustained and integrated approach of this kind, declines and losses of native species are likely to continue.


Scope of report

The Department of Environment, Water, Heritage and the Arts (DEWHA) commissioned research by members of the Institute of Wildlife Research, University of Sydney, to identify sites of high conservation priority impacted on by feral cats in Australia. The key aims of the project were to:

  1. Identify sites around Australia where the impact of feral cats is recognised as a significant threat to native species or ecological communities.

  2. Prioritise the sites identified in (1) by the level of impact by the feral cats.

  3. Identify sites where the impact of feral cats is recognised as a potential significant threat to native species or ecological communities but where the population of feral cats is currently zero or very low, and estimate the degree of potential threat for each site.

  4. Prioritise the sites identified in (2).

  5. Determine for the sites identified in (1) and (2) options for:

a. Eradication if possible;

b. Reduction in cat numbers, including methods for determining optimal density of cats and the methods for obtaining long-term reduction in numbers.

  1. Identify specific feral cat control programs for the sites identified in (1) and (2) and document, where possible:

a. Resources required;

b. How feral cat numbers and impacts are monitored; and

c. Control techniques used.

  1. Identify effective feral cat control programs in locations outside the sites identified in (1) and (2) that may be applicable in these sites and provide details of control techniques, resources and monitoring.

  2. Advise where possible on regional feral cat control programs around the sites identified in (1) and (2) and prioritise areas for regional control.

This report identifies sites of high conservation priority based on broad areas comprising bioregions as defined in the Interim Bioregionalisation of Australia (IBRA), particular sites within these regions, and offshore islands where threatened species have been recorded. Sites discussed in this report are confined largely to areas where those threatened species listed in the Threat Abatement Plan for Predation by Feral Cats (2008) have been recorded. A decision-making tree, based on characteristics of both predator and prey species, is constructed and used to compare and prioritise sites throughout the Australian mainland and offshore islands. This is a flexible tool that can be used to identify sites based on threatened species listed by the Australian Government and/or at the state/territory and regional levels, depending on management objectives.


The domestic cat (Felis catus) is believed to have been introduced into Australia at multiple points along the coastline during the period 1824-1886 (Abbott 2002). The descendants of some of these cats, now feral and largely independent of people for their resource requirements, are now widespread across the Australian mainland, Tasmania and many offshore islands (Burbidge et al. 1997; Abbott 2002) and have been implicated in the status shifting and decline of native mammal species (Dickman et al. 1993; Burbidge et al. 1997).

The primary impact of the feral cat in Australia is via predation on mammals, birds, reptiles, amphibians and some invertebrates. There is also evidence of a potential threat from cats to native species through the dissemination of diseases and parasites (Moodie 1995; Henderson 2009), and competition with feral cats for available resources may negatively impact larger dasyurids, varanids and large raptors (Dickman 1996). The impacts of feral cats on native fauna may be exacerbated when prey species are already negatively impacted by habitat modification; climatic events such as droughts, fires and floods; disease; and changes in food distribution and abundance (Dickman 1996). The impacts also may vary between sites due to differences in climate, landform, habitat, and species richness and diversity - factors that affect the relative abundance of both prey and predator.

The evidently high level and deleterious nature of impacts of feral cats has resulted in the formulation of threat abatement plans at both the national and state/territory levels (Greenaway 2009). Effective implementation of these plans over the Australian mainland and on offshore islands requires the prioritisation of sites of high conservation value for control efforts to preserve threatened native species and ecological communities. Prioritisation of sites of high conservation value provides a basis for targeting those areas of highest feral cat impact or potential impact, and for the distribution of the resources available for cat control programs on the Australian mainland and offshore islands.

The identification of sites of high conservation priority impacted by feral cats is multi-faceted, comprising:

  • assessment of the number of threatened species and the status of threatened species at particular sites,

  • the relative vulnerability of each threatened species to cat predation based on characteristics of these prey species including size (e.g., critical weight range (Dickman 1996)), habitat use, cycle (diurnal or nocturnal), locomotion and defenses, and

  • assessment of whether any cat control programs are in place or are planned for bioregions on the Australian mainland, or specific sites including national parks, nature reserves and offshore islands.

In 2006, Reddiex et al. provided an overview of the patterns of control and monitoring of vertebrate pests on the Australian mainland and offshore islands based on a survey of the actions of conservation-focused organisations between 1998 and 2003. The authors reported that feral cat control operations in Australia increased fivefold in 2002 and that 57.5% of feral cat control operations were ongoing, whilst 27.5% had ceased because the goal was attained. This relatively high success rate (compared to 0.5% foxes and 0% for wild dogs) reflected the concentration of cat control programs on islands and within predator-proof sites on the mainland (Reddiex et al. 2006).

However, between 1998 and 2003, the mean area of control operations for feral cats (>3,355 ha) fell well below that of foxes (>93,643 ha) or wild dogs (>22,534 ha), despite a much wider distribution of cats in Australia than either foxes or wild dogs. Most cat control operations occurred in the south-west and south-east of the mainland, or on offshore islands.

The relative abundances of cats among habitats in Australia are difficult to assess because of habitat-specific variation in the detectability of cats, and because of variations in the methodology used in different studies. Reddiex et al. (2006) reported that most feral cat control programs were conducted on offshore islands or on mainland sites enclosed by predator-proof fences, and were aimed at ongoing control rather than eradication. Direct and indirect sampling techniques for the assessment of presence/absence and relative abundance of free-living cats in Australia vary in effectiveness between different environments. Factors that may lead to bias in density estimates or estimates of relative abundance include:

  • vegetative cover, including tree species – feral cats are more visible in open, sparsely vegetated habitats and use vegetation for concealment when hunting or moving between sites;

  • substrate – tracks of feral cats are more easily discernible on soft, sandy substrate than on harder, more stony or vegetated substrates (Denny 2005);

  • proximity of sampling sites to runways (e.g., tracks, roads, dune crests) – feral cats have been recorded preferentially using runways (Mahon et al. 1998, Denny 2005), so estimates of cat activity may under- or over-estimate the abundance of cats if runways are excluded from or included in detection studies;

  • flowing or dry creek lines and water courses – at sites where creeks and water courses are most usually dry (e.g., arid areas) signs of feral cat presence such as tracks and scats are more easily discovered than in habitats with frequently flowing creek lines or water courses;

  • domestic stocking rates – tracks and scats of larger, hard-footed domestic stock may obscure tracks of the smaller, soft-footed feral cats;

  • human and vehicular traffic movements – feral cat tracks and scats may be obscured along roadways and tracks by human and vehicular movements; and

  • densities of medium to large ground-dwelling mammals – signs of other mammalian pest species (foxes and wild dogs) may be confused with those of feral cats (Denny 2005), and signs of the presence of feral cats may be obscured at sites of abundant larger marsupials such as kangaroos, wallabies and wombats.

Published densities of feral cats in the Australian literature range from 0.03 cats km-2 (Ridpath 1990, Burrows and Christensen 1994) to 4.7 cats km-2 (Newsome 1991), although higher densities have been reported on both offshore islands (Domm and Messersmith 1990) and at resource-rich sites such as rubbish dumps (Denny et al. 2002). Variations in feral cat densities in Australia have been related to time of year, with cat densities higher in summer when juvenile cats are dispersing, than in winter (Jones and Coman 1982); and prevailing climatic conditions, with cat densities higher during non-drought than during drought periods when the relative abundance of prey species is higher (Newsome 1991, Burrows and Christensen 1994). Densities of cats have also been related to proximity to highly modified and resource-rich habitats such as rural townships or rural refuse sites (Read and Bowen 2001; Denny 2005). Throughout the world, the highest cat densities have been recorded in urban/peri-urban habitat, next highest on islands, and lowest at mainland sites remote from human activity (Liberg et al. 2000). These geographical variations in cat densities are related to the relative abundance and distribution of food resources, with the greatest cat densities recorded where food abundance is relatively high and clumped and lowest where the food abundance is low and dispersed (Liberg et al. 2000).


Several limitations are inherent in developing prioritised listings of sites throughout the Australian mainland and on offshore islands where feral cats have been reported, or are likely to, have negative impacts on biodiversity. Such limitations include:

  • Lack of reliable data on feral cat densities or relative abundance throughout the continent – this precludes the use of basic measures to formulate a methodology for prioritising sites impacted by feral cats. Consequently, alternative data (discussed later in this document) were used for this project.

  • Lack of reliable data on causal relationships between cat predation/disease dissemination/competition and extinction/status shifting of native prey at the species level.

  • Lack of data on cat control programs - apart from relatively large, well-documented cat control/eradication programs on islands, in predator-proof exclosures, and sites where above-ground baiting is feasible, there are few data available on cat control programs at specific sites.

  • Variations in land tenure and state/territory legislation relating to sites where cats are known to, or may possibly have an impact – land management and relevant legislation are both central to feral cat control programs and the limited time frame for this project precluded investigations into the feasibility of instigating control at a number of sites.

The methodology that we adopt here – a rank-scoring system – acknowledges these limitations and attempts to provide an objective and repeatable means by which managers can assess the likely impact of feral cats on native fauna on land under their jurisdiction. By using the rank-scoring approach first at the bioregional scale and then at a smaller site-specific scale, we also show how the methodology can be used to develop a prioritised list of places where cat impacts on threatened species can be expected to be greatest, and hence where control efforts may best be directed.


Threatened species potentially impacted by feral cats

The native species considered here to be at risk of predation by feral cats are those listed in Appendix A of the Threat abatement plan for predation by feral cats (TAP) (2008). This list, specifying species and subspecies considered to be vulnerable, endangered or critically endangered under the TAP, formed the basis for identifying and prioritising sites on mainland Australia and offshore islands impacted by feral cats. The threatened species listed in the TAP (2008) for predation by feral cats are shown in Table 1. Note that, following Appendix A in TAP (2008), listed critical habitats and some unlisted taxa that could be affected by feral cats are also given.

Table 1: Threatened species and critical habitats that may be adversely affected by feral cats


Scientific name

Common name

Current status

Listed threatened species that may be adversely affected by feral cats


Cereopsis novaehollandiae grisea

Cape Barren goose (southwestern), Recherche Cape Barren goose


Chalcophaps indica natalis

Emerald dove (Christmas Island)


Cinclosoma punctatum anachoreta

Spotted quail-thrush (Mt Lofty Ranges)

Critically endangered

Cyanoramphus cookii
(listed as Cyanoramphus novaezelandiae cookii)

Norfolk Island green parrot


Dasyornis brachypterus

Eastern bristlebird


Diomedea exulans

Wandering albatross


Fregetta grallaria grallaria

White-bellied storm-petrel (Tasman Sea), white-bellied storm-petrel (Australasian)


Gallirallus philippensis andrewsi

Buff-banded rail (Cocos [Keeling] Islands)


Birds (continued)

Halobaena caerulea

Blue petrel


Lathamus discolor

Swift parrot


Leipoa ocellata



Leucocarbo atriceps purpurascens
(listed as Phalacrocorax purpurascens)

Imperial shag (Macquarie Island)


Lichenostomus melanops cassidix

Helmeted honeyeater


Macronectes giganteus

Southern giant-petrel


Malurus coronatus coronatus

Purple-crowned fairy-wren (western)


Malurus leucopterus leucopterus

White-winged fairy-wren (Dirk Hartog Island), Dirk Hartog black-and-white fairy-wren


Melanodryas cucullata melvillensis

Hooded robin (Tiwi Islands)


Neophema chrysogaster

Orange-bellied parrot

Critically endangered

Pachycephala pectoralis xanthoprocta

Golden whistler (Norfolk Island)


Pachyptila turtur subantarctica

Fairy prion (southern)


Pardalotus quadragintus

Forty-spotted pardalote


Pedionomus torquatus



Petroica multicolor multicolor

Scarlet robin (Norfolk Island)


Pezoporus occidentalis

Night parrot


Pezoporus wallicus flaviventris

Western ground parrot


Pterodroma heraldica

Herald petrel

Critically endangered

Pterodroma leucoptera leucoptera

Gould’s petrel


Pterodroma mollis

Soft-plumaged petrel


Pterodroma neglecta neglecta

Kermadec petrel (western)


Birds (continued)

Sterna vittata bethunei

Antarctic tern (New Zealand)


Sterna vittata vittata

Antarctic tern (Indian Ocean)


Stipiturus malachurus intermedius

Southern emu-wren (Fleurieu Peninsula), Mount Lofty southern emu-wren


Thalassarche chrysostoma

Grey-headed albatross


Thalassarche melanophris

Black-browed albatross


Turnix melanogaster

Black-breasted button-quail



Bettongia lesueur lesueur

Boodie, burrowing bettong (Shark Bay)


Bettongia lesueur
unnamed subsp.

Boodie, burrowing bettong (Barrow and Boodie Islands)


Burramys parvus

Mountain pygmy-possum


Dasycercus byrnei



Dasycercus cristicauda



Dasycercus hillieri



Hipposideros semoni

Semon’s leaf-nosed bat, greater wart-nosed horseshoe-bat


Isoodon auratus auratus

Golden bandicoot (mainland)


Isoodon obesulus obesulus

Southern brown bandicoot


Lagorchestes hirsutus bernieri

Rufous hare-wallaby (Bernier Island)


Lagorchestes hirsutus dorreae

Rufous hare-wallaby (Dorre Island)


Lagorchestes hirsutus unnamed subsp.

Mala, rufous hare-wallaby (central mainland form)


Lagostrophus fasciatus fasciatus

Banded hare-wallaby, marnine, munning


Leporillus conditor

Wopilkara, greater stick-nest rat


Macrotis lagotis

Greater bilby


Myrmecobius fasciatus



Mammals (continued)

Notoryctes caurinus

Karkarratul, northern marsupial mole


Notoryctes typhlops

Yitjarritjarri, southern marsupial mole


Onychogalea fraenata

Bridled nail-tail wallaby


Parantechinus apicalis



Perameles bougainville bougainville

Western barred bandicoot (Shark Bay)


Perameles gunnii gunnii

Eastern barred bandicoot (Tasmania)


Perameles gunnii unnamed subsp.

Eastern barred bandicoot (mainland)


Petaurus gracilis

Mahogany glider


Petrogale lateralis MacDonnell Ranges race

Warru, black-footed rock-wallaby


Petrogale penicillata

Brush-tailed rock-wallaby


Petrogale persephone

Proserpine rock-wallaby


Phascogale calura

Red-tailed phascogale


Potorous gilbertii

Gilbert’s potoroo

Critically endangered

Potorous longipes

Long-footed potoroo


Pseudomys fieldi

Djoongari, Alice Springs mouse, Shark Bay mouse


Pseudomys fumeus

Konoom, smoky mouse


Pseudomys oralis

Hastings River mouse


Sminthopsis aitkeni

Kangaroo Island dunnart


Sminthopsis douglasi

Julia Creek dunnart


Zyzomys pedunculatus

Central rock-rat



Delma impar

Striped legless lizard


Egernia kintorei

Great desert skink, tjakura, warrarna, mulyamiji




Egernia obiri

Arnhem Land egernia


Eulamprus leuraensis

Blue Mountains water skink


Eulamprus tympanum marnieae

Corangamite water skink


Hoplocephalus bungaroides

Broad-headed snake


Lepidodactylus listeri

Lister’s gecko, Christmas Island gecko



Heleioporus australiacus

Giant burrowing frog


Litoria aurea

Green and golden bell frog


Philoria frosti

Baw Baw frog



Scientific name

Common name

Current status

Unlisted species or taxa that could be adversely affected by feral cats


Amytornis textilis textilis

Thick-billed grasswren (western)

Phaethon rubricauda westralis

Red-tailed tropicbird

Puffinus assimilis

Little shearwater

Zosterops tenuirostris

Norfolk Island white-eye, slender-billed white-eye


Cryptoblepharus egeriae

Blue-tailed skink

Emoia nativitatis

Forest skink

Listed critical habitat

Diomedea exulans (Wandering albatross) — Macquarie Island

Thalassarche chrysostoma (Grey-headed albatross) — Macquarie Island
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