Land clearing versus invasive species: Which is the biggest threat?

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Feral cat with galah. Photo: Mark Marathon | CC BY-SA 4.0
Land clearing in Queensland from 2013 to 2015 was estimated in a WWF report to kill 2.6 million birds a year. This is a shocking number, but even more shocking is that cats kill more birds than this in just three days. Photo: Mark Marathon | CC BY-SA 4.0

Land clearing is a scourge on this land but invasive species are just as big a threat to Australian wildlife.

Two recent popular articles have downplayed the threat of invasive species. They were penned in response to the now-former Threatened Species Commissioner, Gregory Andrews, downplaying the threat of land clearing. In an interview on ABC Radio National, Andrews claimed feral cats were a far greater threat than land clearing.

He was wrong; perhaps he was confusing the threats to mammals (for whom cats are the major threat) with threats to all species.

In response, The Conversation featured an article by ecologists Brendan Wintle and Sarah Bekessy arguing land clearing is a bigger threat to plants and animals than invasive species (1) and New Matilda published an article by Suzanne Milthorpe entitled It’s the Habitat Destruction, Stupid. (2)

We at the Invasive Species Council think it is wrong to downplay either threat. Each has caused dozens of extinctions and imperils hundreds more Australian species.

The rising rates of land clearing in Queensland and New South Wales are a national disgrace, but so too are the failures of biosecurity that have enabled recent establishment of the likes of myrtle rust, yellow crazy ants and red fire ants as well as the continued spread of many other harmful invaders.

It is not the case, as Wintle and Bekessy contend, that invasive species are mainly a problem in cleared landscapes. ‘It’s all about habitat loss, because habitat loss makes all other threats more acute,’ they say. Invasive species also cause extinctions in national parks and other ‘natural’ landscapes.

Bulldoze trees, and you wipe out plants and animals. Introduce a new predator, competitor or disease, or let a weed take over, and you can just as effectively push species to extinction.

As documented below, invasive species have been overwhelmingly the major cause of animal extinctions in Australia – primarily responsible for at least three-quarters of mammal extinctions, half the bird losses and all frog and reptile losses – while habitat destruction has been the main cause of plant extinctions.

Current threats are more difficult to count – threatened species are typically subject to multiple pressures. According to a 2011 assessment (by Megan Evans and six colleagues) of about 1300 species on the national threatened species list, habitat loss (which includes livestock grazing) is a major threat for 81% and invasive species for up to three-quarters of listed species. (3)

We can’t be precise about the figure for invasive species because the researchers distinguished between ‘Introduced plants or animals’ (61%) and ‘diseases’ (15%), most of which are introduced, and there is likely to be some overlap in the species they affect, which would lead to double counting. Inappropriate fire regimes are a third major threat, affecting 43% of listed species.

Patterns of decline vary. Across Australia’s northern savannas and the deserts, where land clearing has been minimal, invasive species and fire are the main threats. Where substantial clearing and logging have occurred – across the southwest and the southeast, in populated coastal areas, in some grazing areas and on islands – habitat loss and invasive species are typically the major threats. The major threat for marine species has been over-exploitation.

Most of the following information has come from an Invasive Species Council report by Tim Low, Invasive Species: A Leading Threat to Australia’s Wildlife. (4)


According to The Action Plan for Australian Mammals 2012, invasive species – mainly cats and foxes – were the primary cause of extinction for 22 species, and a probable or possible factor for five others. (5) Habitat loss was the main cause of extinction of only one species, the toolache wallaby. Habitat degradation caused by livestock and feral herbivores such as rabbits is likely to have contributed to some extinctions. For current threats, feral cats are the leading problem and red foxes are third, after inappropriate fire regimes. Habitat loss is fourth.


Seven bird species are listed as extinct under the EPBC Act (13 subspecies are also listed). Most are island birds, and invasive predators, particularly black rats, are thought to have been the main cause of extinction of four species. According to the 2011 Evans study mentioned above, 87% of listed birds are threatened by habitat loss and 81% by introduced plants and animals.

Land clearing in Queensland from 2013 to 2015 was estimated in a WWF report to have killed 2.6 million birds a year. (6) This is a shocking number, but even more shocking is that cats kill more birds than this in just three days. A 2017 assessment by John Woinarski and colleagues found that cats kill some 377 million birds a year in Australia, including those of 71 threatened species. (7) The rate is highest in arid Australia (uncleared) and on islands.


The EPBC Act lists four frogs as extinct, most likely due to the disease caused by chytrid fungus. An additional two species are also feared extinct due to this fungus, which arrived in Australia no earlier than 1978. According to the Evans study, habitat loss threatens 73% of listed frogs, disease threatens 73% and introduced plants and animals threaten 86%.


No species are listed as extinct, but three lizard species (possibly four) have recently been lost from Christmas Island (two species survive in captivity), probably due to introduced predators, mostly wolf snakes but also cats, black rats and Asian giant centipedes. As noted in the Invasive Species Council report, these lizards all disappeared from a large national park, ‘a graphic example of how habitat protection does not guarantee species survival if invasive species run free.’ According to the Evans study, 92% of listed species are threatened by habitat loss and 71% by introduced plants or animals.


Australia’s one extinct-in-the-wild fish, the Pedder galaxias, was lost to invasive brown trout and another galaxias, which invaded after the drowning of Lake Pedder, but the species was saved by translocation to other sites. According to the Evans study, 80% of listed fishes are threatened by habitat loss, 67% by introduced plants or animals and 7% by disease.


Under the EPBC Act, 37 plant species are listed as extinct. For 33 of these, the causes of extinction are not specified, but the main reason is likely to have been habitat loss. According to the Evans study, habitat loss is a major threat to 80% of the assessed species and introduced species plus diseases to 70%. A 2007 assessment of the ‘threat syndromes’ of Australian plants (by Mark Burgman and others) found that habitat loss was overwhelmingly the main threat to plants in the past but that species numbers threatened by weeds, disease and feral grazers have escalated in recent times to rival numbers affected by clearing.(8) The recent arrival of myrtle rust in Australia and a growing list of emerging pathogens overseas imply the disease threat will be much greater in future.

Australia can easily stop broadscale clearing, but preventing new invasive species and controlling the existing ones is much harder and far more expensive.


1. Wintle B, Bekessy S. Let’s get this straight, habitat loss is the number-one threat to Australia’s species [Internet]. The Conversation. 2017 [cited 2018 Jan 28]. Available from:
2. Milthorpe S. It’s the habitat destruction, stupid [Internet]. New Matilda. 2017 [cited 2018 Jan 28]. Available from:
3. Evans MC, Watson JEM, Fuller RA, Venter O, Bennett SC, Marsack PR, et al. The spatial distribution of threats to species in Australia. BioScience. 2011;61(4):281–9.
4. Low T. Invasive species: A leading threat to Australia’s wildlife [Internet]. Invasive Species Council; 2017. Available from:…/Invasive-species-A-leading-threat-to-Australias-wildlife.pdf
5. Woinarski JC, Burbidge AA, Harrison PL. The Action Plan for Australian Mammals 2012 [Internet]. Collingwood, VIC: CSIRO Publishing; 2014 [cited 2018 Jan 28]. Available from:
6. Cogger H, Dickman C, Ford H, Johnson C, Taylor M. Australian animals lost to bulldozers in Queensland 2013-15. WWF-Australia technical report. [Internet]. WWF-Australia; 2017. Available from:>
7. Woinarski JCZ, Murphy BP, Legge SM, Garnett ST, Lawes MJ, Comer S, et al. How many birds are killed by cats in Australia? Biol Conserv. 2017 Oct 1;214:76–87.
8. Burgman M, Keith D, Hopper S, Widyatmoko D, Drill C. Threat syndromes and conservation of the Australian flora. Biol Conserv. 2007 Jan;134(1):73–82.

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Help protect NSW!

Our expert team has written a list of policy asks detailing exactly what the next NSW government needs to do to stamp out some of the worst invasive species impacts across the state. But they will only become a reality if every key political candidate at the 2023 NSW state election hears about it from you!

Dear National Deer Management Coordinator,

Please accept this as a submission to the National Feral Deer Action Plan.

[Your personalised message will appear here] 

I am very concerned about the spread of deer and am pleased that a national plan has finally been developed. Without urgent action, funding and commitment from all levels of government it is clear that feral deer will continue to spread and damage our environment.

The feral deer population in Australia is growing rapidly and spreading across the country, damaging our natural environment, causing havoc for farmers and foresters and threatening public safety. Unlike much of the world where deer are native, our plants and wildlife haven’t evolved to deal with these heavy hard hooved animals with a voracious appetite.
With no natural predators and an ability to adapt to almost all environments, they could occupy almost all of Australia unless stopped. Despite this, state and territory governments have been slow to respond and in Victoria and Tasmania they are still protected by law for the enjoyment of hunters.

This plan should be adopted by all governments but must also be underpinned by dedicated funding and clear responsibilities. A plan without funding or accountability is a plan that will fail and Australia cannot afford for this to fail.

In order to prevent the spread of feral deer and reduce their impact on our native wildlife, ecosystems and agriculture, I ask that the following recommendations be adopted for the final National Feral Deer Action Plan:

1. All federal, state and territory governments should adopt the National Feral Deer Action Plan and declare feral deer to be a priority pest animal species.

2. All federal, state and territory governments should commit to:

  • Contain deer to the existing large population areas.
  • Reduce and eradicate smaller and isolated populations.
  • Protect important environmental assets such as world and national heritage areas.
  • Develop and fund regional plans and strategies to manage deer populations which involve land managers across all tenures.

3. In order to drive action and the success of this plan, there should be dedicated Commonwealth funding and support for:

  • A permanent national feral deer coordinator position.
  • A permanent federal feral deer action committee with representatives from the commonwealth and state and territory governments and the environmental and agricultural sectors.
  • An ongoing public education campaign on feral deer.
  • A network of regional feral deer coordinators to drive local action across tenures.

4. The expected outcomes for the plan need to be more ambitious, with clear interim targets including:

  • Within one year, all States and Territories should have in place arrangements to implement the National Feral Deer Action Plan, including allocating dedicated funding for implementation.
  • Within one year, feral deer management plans should be developed for key environmental assets of national significance, including the Tasmanian Wilderness World Heritage Area, the Greater Blue Mountains, the Australian Alps, the Gondwana Rainforests and the Wet Tropics of Queensland.
  • Within five years coordinated landscape scale management should be in place where land owners, land managers, government and community are demonstrably working together.

5. A national feral deer containment map with three zones should be adopted. It should be more ambitious than the zone map in the current draft plan and there should be greater clarity in the naming of the zones. Improvements that should be adopted include:

  • Renaming the zones to better reflect the management intention to ‘Containment Zone 1’ (the current large population zone), ‘Containment Buffer Zone 2’ (the current buffer zone) and ‘Eradication and prevention Zone 3’ (the current small isolated population zone).
  • The NSW northern rivers area should be in the eradication and prevention zone as there are few feral deer currently in this region and eradicating isolated populations and preventing spread into this area is still possible.
  • The whole of South Australia should be in the eradication and prevention zone as eradication is the goal of the SA Government.
  • The Tasmanian region in the containment zone should be smaller to reflect greater ambition and potential for eradication of deer populations.
  • In eastern Victoria areas such as Wilson’s Promontory, Westernport islands and the Mornington Peninsula should be in the eradication and prevention zone.

6. There should be consistent laws and regulations across all states and territories that:

  • Recognise feral deer as a pest animal and treat them as such.
  • Establish a clear responsibility for all landholders and managers to be involved in feral deer control programs.
  • Set clear penalties to stop the wilful or negligent release of feral deer.
  • Prevent new deer farms in areas where no feral deer are present and phase out all deer farms in the eradication and prevention zone.
  • Enable enforcement of compliance, including on government land.

I support the follow principles being adopted in the final National Feral Deer Action Plan:

  • Feral deer are a pest and should be treated as such on all tenures, except on approved deer farms.
  • Federal, state and territory governments have a responsibility to fund the outcomes under this plan.
  • All land managers in areas where feral deer are present have a responsibility to be involved in feral deer control programs.
  • The focus of management efforts should be on eradication of isolated, satellite populations, protection of key environmental assets currently impacted and stopping the spread to new regions.
  • Feral deer control should be undertaken humanely, safely and professionally according to agreed protocols and all tools which meet this criteria should be adopted, including aerial control.
  • Funding for coordination, regional planning and community engagement is necessary for effective feral deer management.
  • Ongoing management and follow up control efforts are required to achieve long lasting results.
  • Rules and regulations should be consistent across jurisdictions and land tenures.
  • Recreational hunting is not an effective strategy for feral deer control and should not be relied upon.
[Your name]
[Your email address]
[Your suburb], [Your state]