The impacts of the cane toad are listed as a key threatening process under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). This means that cane toads are identified as threatening or potentially threatening the survival, abundance or evolutionary development of native species or ecological communities. The Australian Government is acting to understand and manage these impacts on our biodiversity.
This document outlines what we know about cane toads, what’s currently being done and what we can do about protecting our vulnerable wildlife, in all its diversity, from the future impacts of this toxic pest.
Cane toads are large, robust amphibians which are native to Central and South America. They are extremely hardy animals and voracious predators of insects and other small prey. These are the qualities that led to their introduction to Australia as a means of controlling pest beetles in the sugar cane industry in 1935, before the use of agricultural chemicals became widespread.
Cane toads have an impressive array of highly toxic chemical defences available to them at almost all stages of their lives. The toxins occur in their skin and organs and can be secreted by large glands at the back of the animal’s head when it is threatened. As a result, toads will poison many predators that attempt to eat them.
Much anecdotal and some documented evidence exists around cane toad impacts on native predators, including quolls, snakes, goannas and freshwater crocodiles, all of which may be lethally poisoned when they attempt to eat toads. Although some may recover, many individual predators die when they are first exposed to cane toads and populations soon start to decline.
Uncertainty exists as to the degree of recovery of populations of native species that attempt to eat cane toads and are affected by the toad toxins. There is anecdotal evidence that as cane toad infestations persist and become established, some populations of native species begin to recover. Recent research has demonstrated that individual native planigales (relatives of the quoll) will learn to avoid toads if they recover from their first experience of the cane toad toxin (Webb et al. 2008). Research also suggests that populations of black snakes have undergone rapid evolutionary adaptations in behaviour and physiology in response to the presence of cane toads (Phillips & Shine 2004, 2006).
For some species (most notably the quoll), it appears that recovery is, at best, limited. For example, populations of northern quoll were under stress from other factors, but with the arrival of cane toads in the Northern Territory and subsequent rapid population declines, they have been recognised under Federal legislation as endangered and under Northern Territory legislation as critically endangered.
There have been concerns raised regarding the impact cane toads may have on other native frogs or small predators competing for the same resources as the toads. Current research is showing that for populations of frogs in the top end of the Northern Territory there has been minor competition impact on frogs as a result of cane toads (Greenlees 2007). The long term impact of the cane toad on invertebrates (their main source of food) has not yet been examined in detail. However, one study has shown a short term impact on the diversity and abundance of beetles with the arrival of cane toads (Caitling et al. 1999).
As they colonise areas of human habitation, toads can be of frequent nuisance value and a health concern to residents. The risk of children or pets being poisoned from contact with toads is an important consideration.
For Aboriginal people using traditional food sources, the impact of toads on some of the native predator species used as bush tucker (such as goannas) is also of concern.
Cane toads can produce large numbers of offspring and are colonising northern Australia at an increasingly rapid pace. Research from the University of Sydney indicates that they also appear to be evolving adaptations to suit their new environment, enabling the colonising toads to move more quickly.
Cane toads are a national problem. Since their release, cane toads have dispersed across northern and eastern Queensland, the top end of the Northern Territory and they have recently arrived in northern WA. They are also present in northern NSW and their dispersal along flooded creek lines in the arid south-west of Queensland has raised concern that the toads will eventually spread to South Australia via river systems such as the Cooper.
In April 2005, the biological effects, including lethal toxic ingestion, caused by cane toads were listed as a Key Threatening Process under the EPBC Act (Department of the Environment and Heritage 2005). The reasoning for this was that the northern quoll could become further threatened as a result of the cane toad. Also, the ornamental snake and the green and golden bell frog were identified as threatened species likely to be adversely affected by the arrival of cane toads.
The Australian Government is currently preparing a national cane toad plan under the EPBC Act. The plan will address the impacts of cane toads on native species and ecological communities. In addition, community ground-control work and research projects on cane toads have been funded under the Caring for our Country initiative.
Research with a national focus
CSIRO has conducted research relating to broad scale biological control of cane toads. Searches were undertaken in the toad’s native (South America) range for species specific pathogens and when this produced no control agent, research began into a self disseminating genetically modified virus to act as a broad scale biological control. This work was discontinued due to technical hurdles and the prospect of limited support for the release of a genetically engineered virus if the project was successful.
Various research projects have been carried out by CSIRO, state governments and universities to examine the impacts of toads on native species, but a better understanding of the long term implications for Australia’s biodiversity is needed.
Future research will be subject to comprehensive technical assessments by a scientific panel.
Management of Australian Government controlled lands
Cane toads have an impact on Australian Government controlled lands, including Kakadu National Park, several World Heritage Areas and Indigenous Protected Areas. Impacts on other areas of land managed by the Australian Government are likely in the future. Actions in these areas could provide case studies for improving biodiversity through measures to exclude or lessen the impact of toads.
The cane toad advisory group
The cane toad advisory group is comprised of government representatives from the affected states and the Northern Territory as well as the Australian Government and the Invasive Animals Cooperative Research Centre. The cane toad advisory group falls under the Vertebrate Pests Committee and is guided by the Australian Pest Animal Strategy. This group provides a means for monitoring the spread of cane toads and provides access to expert advice.
States and the Northern Territory
The affected states and the Northern Territory have funded research on monitoring impacts of toads and understanding the toad’s vulnerabilities. They have also taken a role in coordinating community action such as trapping and manual removal of cane toads and in coordinating public information on options for dealing with toads. Importantly, the states and the Northern Territory have also played a role in educating members of the public involved in community programs on the importance of distinguishing toads from native frogs. Local governments are also frequently involved in community cane toad removal projects, particularly in urban environments, where residents are concerned at the risk posed to children and pets. Industry has become involved – developing and supplying traps and toxins suitable for use in domestic or local situations.
Due to the vast scale of the cane toad infestation and the absence of a broad-scale biological solution, eradication (except locally) is not practicable.
Focussing on positive biodiversity outcomes through decreasing the impact of toads and containing their spread offers the best strategy for the future.
Recent research has documented the ability of some native species to adjust their behaviour and avoid interactions with cane toads if they can survive their initial exposure to toad toxins. This has provided a promising lead for researchers looking at ways of avoiding the dramatic impacts of the arrival of “frontline toads” on native predators, such as the quoll.
Preventing cane toads from arriving on toad-free islands will be an important part of future cane toad management. Additionally, protecting discrete areas of high biodiversity value, using the best available trapping and exclusion techniques, is important.
a) Specific actions
A national cane toad plan will provide for the research, management and other actions necessary to reduce the key threatening process (i.e. biological effects, including lethal toxic ingestion, caused by cane toads) to an acceptable level in order to maximise the chances of the long term survival in nature of native species and ecological communities affected by the process.
b) Scientific research
The biodiversity impacts of cane toads on Australian wildlife are complex and not yet fully understood. As a result, studies are underway which will help clarify the severity of cane toad impacts on native predators and ascertain ecosystem level impacts of cane toads. Research to improve the ways in which the biodiversity impacts of cane toads can be better managed at a local scale is also being conducted. This will allow for improved protection of identified at risk species.
A review of research undertaken by the CSIRO into a genetically modified, self-disseminating virus to control cane toads was conducted by an independent scientific panel in 2008. The review, which recommended discontinuation of this biological control project, included possible areas for consideration for future research and is available at: www.environment.gov. au/biodiversity/invasive/publications/cane-toad/2008.html
a) Manual removal / exclusion
To date, community projects involving manual removal and exclusion of cane toads have been coordinated through the affected states, the Northern Territory and local governments. The Australian Government has delivered funding to some of these groups through the Caring for our Country initiative as part of a $2 million commitment on cane toads. Independent assessment of these projects has shown no evidence that the spread of the toads has been slowed in the WA/NT border region. However, successful local eradication has been reported from Port Macquarie NSW, where conditions are more marginal for the species.
Community group involvement in small scale exclusion fencing of areas of high priority biodiversity, or in quarantine actions to prevent inadvertent movement of toads, may be a more appropriate use of time and resources in areas where environmental conditions for toads are optimal. Focus on manual removal in areas where environmental conditions for toads are marginal offers better opportunity for positive biodiversity outcomes from this method.
b) Information dissemination
With community interest in cane toads at very high levels, production of quality information relating to the impact of the species, the local and broader scale options for reducing cane toad impacts and the role that individuals and communities are capable of playing, is very important.
Additionally, education on identification of local native frog fauna and the potential for spread of amphibian disease in toad removal projects, if appropriate hygiene regimes are not followed, needs to be highlighted. State and territory governments and community groups have worked together very effectively on producing and disseminating this information.
Coordination of effort on cane toads (including research, monitoring and education) could be directed through a technical group such as the Invasive Animals Cooperative Research Centre. This would enable efficient gathering and dissemination of information, together with the technical expertise to independently assess research and monitoring options and requirements.
Research can help us understand the real biodiversity impacts of cane toads and will potentially lead to innovative methods to manage these impacts. As we learn more about the biology of the cane toad in Australia we will better understand the species’ vulnerabilities and be better placed to target local containment or eradication campaigns. Research can also help us identify areas where appropriate exclusion or quarantine measures will protect important areas of biodiversity that are particularly under threat.
Alford, RA, Brown, GP, Schwarzkopf, L, Phillips, B. & Shine, R 2008, ‘Comparisons through time and space suggest rapid evolution of dispersal behaviour in an invasive species’, Wildlife Research, vol. 36, no. 1, pp. 23–28.
Catling, PC, Hertog, A, Burt, RJ, Wombey, JC & Forrester, RI 1999, ‘The short-term effect of cane toads (Bufo marinus) on native fauna in the Gulf Country of the Northern Territory’, Wildlife Research, vol. 26, pp.161-185.
Department of the Environment and Heritage 2005, Key threatening process – ‘The biological effects, including lethal toxic ingestion, caused by Cane Toads (Bufo marinus)’, Department of the Environment and Heritage, viewed 15 February 2010, www.environment.gov.au/biodiversity/threatened/ktp/cane-toads.html
Greenlees, MJ, Brown, GP, Webb, JK, Phillips, BL & Shine R 2007, ‘Do invasive cane toads (Chaunus marinus) compete with Australian frogs (Cyclorana australis)?’, Austral Ecology, vol. 32, issue 8, pp. 900-907.
Phillips, BL & Shine, R 2004, ‘Adapting to an invasive species: Toxic cane toads induce morphological change in Australian snakes’, Proceedings of the National Academy of Sciences of the United States of America, vol. 101, no. 49, pp. 17150-17155.
Phillips, BL & Shine, R 2006, ‘An invasive species induces rapid adaptive change in a native predator: cane toads and black snakes’, Proceedings: Biological Sciences, vol. 273, no. 1593, pp. 1545-1550.
Webb, JK, Brown, GP, Child, T, Greenless, MJ, Phillips, BL & Shine, R 2008, ‘A native dasyurid predator (common planigale, Planigale maculata) rapidly learns to avoid a toxic invader’, Austral Ecology, vol. 33, issue 7, 821-829.