Australasian Science: Australia's authority on science since 1938

Fox Baiting in Tasmania: What’s at Risk?

By Matthew Marrison

With careful attention to the science and planning, targeting foxes in a wildlife-rich environment can be a success.

It’s first light in Tasmania, and across the island thousands of native animals are returning to daytime refuges following a night feeding in pastures and paddocks surrounding cities and towns. These fragmented landscapes, where agricultural land mixes with tendrils of remnant bushland, are rich in resources and attract a wide variety of native wildlife, often to the displeasure of farmers trying to protect crops from hungry wallabies and residents trying to sleep while unruly possums raid rubbish bins.

Such landscapes are also ideal habitat for foxes.

As some native animals return home they pass a small mound of disturbed earth above which distinctive pink flagging tape hangs from a nearby tree or fence post. On rare occasions an animal may pass two or three such mounds if they are travelling a particularly long way.

These mounds are the strategically sited bait stations from Tasmania’s fox eradication program. Each contains a single buried, meat-based bait that is lethal to foxes.

Most native animals will pass by these bait stations without any interest, but a few may pause for a moment to investigate the disturbed earth or the unusual smell. But at what risk?

Very little, according to the results of various studies. This answer might surprise many people, especially if their exposure to the issue is from the media and the frequent but disingenuous headline of “Fox baits put wildlife at risk”.

What might come as an even greater surprise is the fact that many Australian wildlife conservation programs rely heavily on fox baiting using 1080 poison to ensure that native wildlife are protected and can recover from the impacts of foxes. Among them are programs to protect animals that are still common in Tasmania, such as spotted-tailed quolls and eastern barred bandicoots. It is only because of the use of 1080 poison that such animals are able to be protected in some mainland areas.

Unfortunately, deliberately misleading information about 1080 is still widely circulated. The truth of the matter is that fox baiting using 1080 poison is very tightly regulated, very well researched and very carefully planned, particularly in the Tasmanian environment where protecting native wildlife from harm has always been the number one priority of Tasmania’s fox eradication program.

Foremost, the characteristics of the poison itself make it highly suitable for use in Tasmania’s wildlife rich environment.

1080 is a highly water-soluble chemical that was initially developed in the 1900s as a pesticide. While highly poisonous, 1080 is biodegradable and microbes (such as bacteria and soil fungi) will rapidly break it down, in the presence of moisture, to harmless by-products.

In addition, research shows that 1080 is not mobile and does not persist or accumulate in water, soil or the environment. Similarly, 1080 does not persist or accumulate in animal tissues or the food chain. Sub-lethal doses (i.e. doses below the level required to kill an animal) are generally excreted by an animal within 10 hours with little or no physiological damage to the animal.

A study published in the New Zealand Journal of Ecology in 1992 (16(1): 47–9) is a case in point. At Waipoua Forest Sanctuary in New Zealand, streams and rivers were monitored for four months after 100 tonnes of 1080 possum baits were aerially sown over 17,000 hectares of forest. At Rangitoto Island, near Auckland, surface and ground water samples were analysed for six months after 20 tonnes of 1080 possum baits were aerially sown over the 2300 hectare island. Charles Eason and colleagues reported that 1080 was not detected (at a detection level of 0.001 parts per million) in the streams and rivers of the Waipoua forest or in the surface or ground water of Rangitoto Island.

1080 is a highly species-specific poison, making it ideal for use in the Tasmanian environment. Put simply, some species are much more susceptible to it than others; as a general rule of thumb, if you aren’t an Australian native animal then you are in trouble!

The active agent in 1080 is sodium fluoroacetate, a toxin found in 40 or so Australian plants as a defence against herbivore grazing. Because Australia’s native fauna have evolved in a landscape where 1080 was present, they have developed a level of resistance to it. Foxes, having evolved in the northern hemisphere in an environment without 1080, have no natural tolerance.

The difference in species sensitivity means that 1080 can be used in very small doses to target highly susceptible species while providing protection from harm for more resistant species. Foxes are one of the most susceptible species to this poison; the iconic Tasmanian devil is approximately 35 times more resistant to 1080 poison than a fox.

This is the trump card for targeting baiting programs. The Tasmanian fox eradication program uses only 0.003 grams of 1080 per fox bait. This dose is lethal for foxes of any size, but most native animals will require many baits to be at risk of a lethal dose. Further, because 1080 is not accumulative within an animal and sub-lethal doses are generally excreted, the baits required for a lethal dose need to be consumed within a 24–48-hour period.

1080 itself is not lethal: fluorocitrate is the toxic substance, and is produced during the metabolism of the active agent within an animal. Fluorocitrate inhibits the production of energy in cells and can result in cellular death and, if a dose is high enough, death of the animal.

For Tasmanian native carnivores this means a reduced risk of secondary poisoning from the consumption of 1080-poisoned carcasses because much, if not all, of the 1080 is likely to have been metabolised, and the metabolite (fluorocitrate) has little effect when ingested.

As part of the careful planning of the Tasmanian fox baiting program, three factors are controlled to minimise the risk of uptake by native wildlife and maximise the risk to foxes.

Bait placement: Fox baits are buried to reduce the risk to native wildlife while capitalising on the natural foraging behaviour of foxes. The Tasmanian fox eradication program buries fox baits 5–10 cm beneath a cover of soil. Most native wildlife has not evolved to excavate buried food items. Baits that are buried have a reduced smell, which means many native species won’t locate them until baits start to break down (rot), at which time much of the 1080 has also broken down into harmless byproducts. By contrast, foxes are adept at locating buried food items and it is natural behaviour for them to bury surplus food for storage. They have also evolved to locate food items beneath a cover of snow.

Bait availability: Fox baits are widely spaced in the landscape to reduce the chance of uptake by any one animal. The Tasmanian fox eradication program aims to place only 10 fox baits per square kilometre (one bait per 10 ha). Consideration of the home range of Tasmania’s native species has informed this target baiting density to ensure that home ranges, particularly of native species that are more sensitive to 1080, do not overlap with an opportunity to access multiple baits in the landscape. This reduces the potential for uptake of multiple baits by any individual native animal, certainly within the time frame needed for lethal levels of 1080 to be reached.

However, this baiting density still presents significant risk for foxes as they are highly mobile, so their likely encounter rate is high. Most importantly, only one bait is needed for a fox to receive a lethal dose of 1080.

Bait material: Fox baits are meat-based to make them less attractive to native herbivores. The Tasmanian fox eradication program uses meat-based baits that are unpalatable to native herbivores and less attractive to native carnivores. Trials both within Tasmania and on mainland Australia have shown that many native animals are disinclined to eat fox baits. Research has also shown that both bait types are attractive to foxes, and the results from mainland baiting programs attest to the effectiveness of these bait types for targeting foxes.

Fox baits are retrieved at the completion of a baiting program. The retrieval of baits is generally perceived by the community as a measure to reduce risk to native wildlife from the baits, but this is not the case.

The Tasmanian fox eradication program deploys baits on a property for 14–28 days, after which time any remaining baits are retrieved. Studies have shown that, under most conditions, the 1080 has largely biodegraded to harmless by-products after 14 days, and certainly after 28 days.

Bait retrieval is primarily undertaken to ensure that baits that do not contain enough 1080 to kill a fox do not remain in the landscape. Ingestion of a non-lethal bait may result in a fox becoming bait-shy from a learned association between the food item and feeling unwell. This can lead to affected foxes avoiding baits in future, removing the primary tool available for targeting foxes in the landscape.

1080 is currently used as an essential tool in many wildlife protection and conservation programs across Australia, including major programs such as the Western Shield in Western Australia and Southern Ark in Victoria. Under these programs, a number of endangered wildlife populations have undergone dramatic increases as a result of targeted 1080 baiting programs to control or eradicate introduced predators.

1080 fox baiting programs have been critical in the recovery of three mammals in Western Australia (the tammar wallaby, quenda and woylie), two of which have been taken off the endangered fauna list as a result of the successful efforts of the Western Shield Program. Western Australia remains the only area in the world where mammals have been taken off the endangered fauna list.

1080 has now been used in carefully targeted fox baiting programs in Tasmania for more than 10 years. Over this time there has been no evidence to support any significant impacts on native wildlife populations as a result of 1080 fox baiting programs.

One of the animals most often accused of being at risk from fox baiting in Tasmania, the spotted-tailed quoll, is actually found in robust populations in mainland areas where aerial baiting using 1080 has been used for fox and wild dog control over a number of decades. In Tasmania, unpublished research similarly finds that there are no impacts on Tasmanian quoll populations from fox baiting programs.

Tasmania’s fox eradication program seeks to stop the establishment of foxes in Tasmania, which would have devastating consequences for the state’s unique wildlife and environment. To achieve this, the statewide fox baiting program has targeted all areas of highly suitable fox habitat to deny foxes the opportunity to get a foothold. Broadscale baiting with 1080 poison continues to provide the only tool that allows effective landscape targeting of this highly mobile and cryptic pest while minimising any associated risk to native wildlife populations.

While a single 1080 bait poses only minimal risk to most native animals, it poses a significant risk to a fox. In Tasmania it might only be one or two baits that are critical in stopping foxes from getting a foothold.

Perhaps the last word about 1080 should go to the Commonwealth authority responsible for its regulation, the Australian Pesticides and Veterinary Medicines Authority (APVMA). In July 2002, the APVMA began a review of 1080 because of a range of factors including community concerns about poisoning of non-target animals. In January 2008, following extensive review of the issue, the APVMA released Sodium Fluoroacetate (1080): Final Review Report and Regulatory Decision. It concluded that, when appropriate attention is paid to baiting program design, the use of 1080 baits is unlikely to cause significant harm to non-target species, and presents a very low risk to native wildlife populations.

Matthew Marrison is with the Invasive Species Branch, Department of Primary Industries, Parks, Water and Environment.

This article is reproduced from ISSUES magazine's edition on Animal Welfare (www.issuesmagazine.com.au).