Assessing the Risks

When assessing the risks of 1080 fox baiting to individuals or populations of any particular species a number of things should be taken into account, including:

• The physiological sensitivity of the species to 1080 poison (depends on many things principal amongst them the historic exposure of the species to 1080 as it occurs in Australian plants), something that can be experimentally measured.

• How many baits the species might find (depends on the sensory abilities of the animal, how, where and the number of baits placed in a given area — the landscape density).

• How many baits the species might eat within a certain period. To cause death, a lethal dose has to be ingested in a certain time — usually within 2 days because sub lethal doses of 1080 are metabolised. Dried meat baits are too hard for many species to do more than mouth and nibble but many species can eat other baits such as Foxoff (eg non toxic bait trials — Belcher 1998 and DPIW data). There is evidence some species can detect 1080 in baits and avoid eating them (eg the spotted-tailed quoll in Foxoff baits, Kortner et al 2003).

• How much 1080 is left in baits when they are eaten (if they are decomposing, 1080 will have also degraded to a comparable degree).

• The likelihood of the species digesting baits (many carnivores and omnivores regurgitate food containing significant amounts of 1080. There are past records of devils regurgitating 1080-laced food in captive trials).

• The age and health of the individual eating the bait or carcasses of poisoned animals (smaller individuals of a species likely have higher metabolisms and consequent usual higher sensitivity to 1080 and healthy individuals likely have more resistance to 1080)

• The size of individuals in the population at baiting (size effects metabolism and consequent susceptibility to 1080. Individuals of the same species might be different in size in different populations, eg devils on the east coast of Tasmania are much larger than west coast individuals, and there may be many small juveniles just after breeding).

• How the species’ range and abundance overlaps with 1080 baiting (the proportion of the species that might be exposed to baiting).

Physiological sensitivity

The level of physiological sensitivity of a species to 1080 is usually described as the species’ LD50 - that is the mg of 1080 ingested per kg of animal during a very short period that will kill 50% of the individuals exposed (LD = Lethal Dose). Most of the research on LD50s for Australian animals and the potential impacts of 1080 was done on captive animals decades ago by Dr John McIlroy, then at CSIRO, and published in various issues of Australian Wildlife Research (eg McIlroy, 1981a, 1981b and 1981c) and he still gives occasional advice on the matter to DPIW. It is doubtful if this work could ever be substantially expanded or repeated because it involves lethal testing.

LD50s for some Tasmanian animals of obvious interest as potential non-target consumers of fox baits (mainly dried kangaroo meat but also some Foxoff meat compound) are

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We see that kg-for-kg, red foxes are over 13 times as sensitive to 1080 as are spotted-tailed quolls and 30 times as sensitive as devils. The LD50 for spotted-tailed quolls is lower than might be expected considering those for its relatives, the eastern quoll and Tasmanian devil. McIlroy has expressed the opinion the small sample size and temperatures the results were obtained under may have given a too low result. This is born up by most mainland research that shows little effect of fox and wild dog baiting on spotted-tailed quolls (eg Kortner et al 2003).

Persistence of 1080 in baits

In the field, 1080 breaks down by microbe and fungal activity. Meat baits as used in Tasmania are about 120g of fresh kangaroo meat, each dosed with 3mg of 1080 dried hard to about 40g for storage then use (eg Saunders et al 1995). By the time they are set (buried) some 1080 is already broken down and on average they then only contain 2.7mg – a 10% loss. Once buried, degradation of 1080 accelerates, the rate depending on soil conditions (particularly moisture and temperature) and consequent baits degradation. Such degradation of 1080 is well known (eg Saunders et al 2000).

Tasmanian 1080 fox dried meat baits have been tested after different times in the ground in field conditions and on average after 2 days in the ground only 43.3% of 1080 remained, after 5 days there was 28.2% left, after 10 days 19.7% and after 15 days 11.6%. However, there was considerable variation even between neighbouring baits; some in wet places have much less 1080 residue and some in dry places much more than the average.

Number of baits needed to put individuals at risk

Considering the sensitivity of spotted-tailed quolls, devils and foxes to 1080 and degradation of 1080 in buried baits we can calculate how many baits buried for various times need to be eaten by different sized spotted-tailed quolls, devils and foxes within 2 days to have a 50% chance of being killed.

We see below that a very small spotted-tailed quoll will consume an LD50 if it eats most of one freshly layed bait but that same animal would have to eat at least 5 baits within 2 days once they had been in the ground for two weeks to be at similar risk. Similarly a very large spotted-tailed quoll would have to eat more than 4 freshly layed baits to be at risk but more than 30 after two weeks in the ground.

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We see below that even a very small devil (probably not even weaned) needs to eat more than 3 freshly layed baits within 2 days to reach an LD50 and large devils need to eat very many baits in a short period to reach an LD50.

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We see that foxes are extremely susceptible to 1080 baiting and in many circumstances need less than 1 bait to reach an LD50.

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The chances of individuals finding enough baits in a short enough period to be at risk

Extensive testing with foxes on mainland Australia clearly shows they can find baits immediately they are buried; initial take is often high and usually continues until baits and/or foxes are greatly reduced (eg Saunders et al 1995). Limited testing with Foxoff and fresh meat baits with captive and wild spotted-tailed quolls in NSW showed they could detect buried baits but trials only identified this species as taking 2 of 7 baits taken after 3-4 weeks buried adjacent to a spotted-tailed latrine in the wild (Belcher 1998); results consistent with Tasmanian observations considering time buried and that baits were replaced exactly where taken (see below).

Research on take of fox baits without 1080 was undertaken with an isolated, island population of devils (no quolls or foxes present). Initial take was very low (a few % per night) but escalated once baits began to rot, to the point where most baits were taken after 3 weeks. These results were mirrored in places with devils and spotted-tailed quolls, devils and eastern quolls and eastern quolls alone; there are no places exclusively with spotted-tailed quolls in Tasmania. If baits were replaced in a hole where a previous bait had rotted then re-take could be immediate but if placed in a new hole take was very low. Devils in particular would sometimes deeply excavate holes in which baits had rotted.

It seems devils and quolls are not well equipped to find buried baits until they rot or are otherwise smelly (or replaced); probably there has been no need in their evolution. On the other hand, foxes and dogs evolved under conditions of extremely harsh winters where caching and recovering food (or raiding others’ caches) was fundamental to survival. Therefore, these canids are ‘professionals’ at finding buried food (eg Saunders et al 1995, Twigg et al 2000). This does not mean that other species cannot find any buried baits or might even be exposed accidentally (eg during echidna excavations) but it is a clear trend.

There has been considerable questioning of what animals have taken the thousands of baits of the nearly 80,000 sofar set in Tasmania. Checking baits daily allows a reasonable judgment of what might have taken them and in the early days of baiting (2002/3) when daily checks were undertaken about 20 baits were recorded as taken in typical fox style (as seen else where in Australia). Once baiting expanded and baits were only checked at recovery such judgments of take could rarely be made; hence the experiments reported here. If baits were recovered 2-3 weeks after burial few were missing but if it was 3 weeks or more most might be – it seemed a simple fact of rotting and then being found.

In operational fox baiting in Tasmania, baits are buried at a landscape density of 5-10/km2. The number of baits in an animal’s home range can also be considered and how much competition there might be for baits. A large devil might have 100 baits in its home range but that home range would likely be shared by 10-30 other devils plus quolls (and possibly foxes). Thus, the baits available per individual are comparatively few.

The chances of individuals eating enough baits in a short enough period to be at risk

Although they can easily eat soft baits, test have shown that small or even medium sized spotted-tailed quolls and very small devils do not (probably can not) eat very dry and hard baits and it is not until they are independent that they are likely to be under enough nutritional pressure and are strong enough to eat such. Tests on captive mainland Australian spotted-tailed quolls support these results (Belcher 2000).

What actually happens in the field?

Considerable research has been done on effects of 1080 fox baiting on spotted-tailed quolls on mainland Australia (eg Kortner ET al 2003). In Tasmania, experimental 1080 baiting was not carried out but rather, research waited until an operational baiting occurred in an area with enough spotted-tailed quolls to usefully study (near Wynyard).

Although there were too few quolls in the study sites area (and a comparative control site with no baiting) to have statistically robust comparisons of numbers before and after baiting we found individual spotted-tailed quolls similarly persisted in both areas through and after baiting. Importantly, there were breeding females (with pouch young) and free ranging juveniles present in both sites after baiting; there was no identifiable difference between baited and non-baited sites. This work will be repeated as opportunity presents.

In the northern midlands where the effects of 1080 fox baiting on devils was being studied, there was also a ‘background’ population of spotted-tailed quolls. Trapping after a prolonged baiting period showed all elements of a normal devil population in place – breeders and juveniles with no apparent drop in density. Perhaps most interestingly, in the months after this research a substantial drop in numbers of devils due to Devil Facial Tumour Disease occurred and in another 6 months numbers of spotted-tailed quoll seemed to have measurably increased (probably due to decreased competition and predation from the fewer devils) and has stayed high with an apparently normal mix of breeders and juveniles. DFTD it seems has absolutely overwhelming effects (even if indirect) compared to fox baiting.

In an area in which Foxoff meat compound baits were operationally used extensive capture-mark-recapture studies were done of large local populations of Tasmanian bettongs Bettongia giamardi and brushtail possums Truchosaurus vulpecula, two species likely to eat these baits. Very few Foxoff baits were taken and there was no difference in population change between the baited site and a control site.

These Tasmanian ‘pilot’ studies suggest there is little if any damage to local populations of spotted-tailed quoll, Tasmanian devils, Tasmanian bettongs or brushtail possum from 1080 fox baiting in Tasmania as is known to have severe effects on fox populations on mainland Australia (eg Saunders et al 1995).

State-wide Effects

A final check can be made by looking at what proportion of Tasmania’s spotted-tailed quoll and devil population might be exposed to 1080 fox baiting. Sofar, 1080 fox baiting has only touched the fringe of Tasmania’s core spotted-tailed quoll habitat and perhaps less than 2-3% of Tasmania’s spotted-tailed quolls have been in baited areas. Similarly perhaps 5% of Tasmania’s devils have been in baited areas. These areas and percentages may increase by half with planned fox baiting but, even then the reality is little or no effect on a small proportion of the State’s populations of these important species.

References
Belcher, C. (1998). Susceptibility of the tiger quoll, Dasyurus maculatus, and the eastern quoll D. viverrinus, to 1080-poisoned baits in control programmes for vertebrate pests in eastern Australia. Wildlife Research 25, 33-40.
Belcher, C. (2000). The ecology of the Tiger Quoll Dasyurus maculatus, in south-eastern Australia. Unpublished PhD thesis, Deakin Uni.
Kortner, G., Gresser, S. and B. Harden (2003). Does fox baiting threaten the spotted-tailed quoll, Dasyurus maculatus? Wildlife Research 30, 111-118.
McIlroy, J. C. (1981a). The sensitivity of Australian mammals to 1080 poison. 1. Intraspecific variation and factors effecting acute toxicity. Australian Wildlife Research 8, 369-383.
McIlroy, J. C. (1981b). The sensitivity of Australian mammals to 1080 poison. 11. Marsupial and eutherian carnivores. Australian Wildlife Research 8, 385-399.
McIlroy, J.C. (1981). The sensitivity of Australian animals to 1080 poison.1X. Comparisons between the major groups of animals, and the potential danger non-target species face from 1080 poisoning campaigns. Australian wildlife Research 13, 39-48.
Saunders, G., McLeod, S. and B. Kay (2000). Degradation of sodium monoflouroacetate (1080) in buried fox baits. Wildlife Research 27, 129-135.
Twigg, L., Eldridge, S., Edwards, G., Shakeshaft, B., dePeru, N. and N. Adams (2000). The longevity and efficacy of 1080 meat baits used for dingo control in central Australia). Wildlife Research 27, 473-481.

Other Useful Reading
Kinnear, J.E. (2003). Eradicating the fox in Tasmania: A review of the Fox Free Tasmania Program. Unpublished report to DPIWE, Hobart.
Saunders, G., Coman, B., Kinnear, J. and M. Braysher (1995). Managing vertebrate pests: Foxes. Australian Government Printing Service, Canberra
Saunders, G., Lane, C., Harris, S. and C. Dickman (2006). Foxes in Tasmania: A Report on the Incursion of an Invasive Species. IACRC, Canberra.

Nick Mooney is a wildlife biologist with DPIW and has been working with Tasmanian wildlife for more than 30 years. Amongst other hats, he pioneered Tasmanian rehabilitation and conservation of raptors including eagles in forestry, has monitored reports of Thylacines and foxes, helped with responses to newly discovered diseases, whale strandings and oil spills and developed practical conservation of devils and innovative wildlife tourism. Most recently he kicked off the response to Devil facial Tumour Disease and has been giving advice for the response to recent evidence of foxes in Tasmania. Nick is assessing the potential ecological effects of DFTD, foxes and cats; he sees the biggest ecological threat as establishment of foxes because of DFTD, a process that could cause the ultimate long term threat to devils (his favourite animal).

Nick Mooney

There has been a recent spate of public concern over the effect that 1080 baiting targeting the red fox Vulpes vulpes in Tasmania might have on the spotted-tailed quoll Dasyurus maculatus and the Tasmanian devil Sarcophilus harrisii.

Considerable research has been done on that quoll species on mainland Australia, studies augmented by work in Tasmania on both it and devils.