Image for Letter to the Fox Eradication Program

Dear Fox Eradication Program,

Regarding your letter of 15th September, 2011, requesting permission to lay 1080 poison on our Derwent Valley property to kill any possible foxes we might be harbouring: -

I have considered this request carefully, but find I am lacking the required information to provide a reasoned answer, despite your brochures and website information.  I wouldn’t want you killing my quolls, Tas. devils, bandicoots and small macropods, nor neighbours’ dogs or cats.  On the other hand, if I was confident that you could be 100% certain of killing any local foxes, if they exist, then I would possibly take this risk.  Here are some of the problems with your program as I see things: -

1.  Uncertainty that buried Foxoff bait will kill Tasmanian foxes.

The reviews into the fox eradication program by the Invasive Animals CRC in 2006 (http://www.feral.org.au/wp-content/uploads/2010/03/FoxReview_Web.pdf) and by Landcare Research in New Zealand in 2009 (http://www.dpiw.tas.gov.au/internnsf/Attachments/PWOD-7WC3KE/$FILE/Fox_2009%20NZ%20Review.pdf) provide references to most of the research that has been undertaken to study the effectiveness of buried Foxoff in killing foxes. 

These references are also all cited in the detailed and authoritative 2007 Saunders and McCloud report   “Improving Fox Management Strategies in Australia” (  http://www.feral.org.au/wp-content/uploads/2010/03/final.proof_fox_collated_book.low.res.pdf  )  As descried therein, there are quite a few investigations from mainland Australia where the poison bait has been applied on the ground, mainly by aircraft, but surprisingly few where the bait is buried to minimise non target uptake, such as in Tasmania. 

In fact there are only 4 references to uptake of buried bait, all of them where several days’ free feed provision encouraged food consumption prior to the poisoning event.  Average fox kill in these 4 reports was 77%, but varied enormously.  Saunders and McCloud cite 70% kill as a “successful kill”.  A serious problem with such trials is that some foxes need to be trapped and fitted with radio tracking collars prior to poisoning so that it can be noted how many of them are subsequently poisoned.  Since foxes are rather trap shy, it is the least wary animals that get caught.  These are also more likely to be less poison wary than the more cunning general local fox population.  The other big problem in extrapolating to Tasmania is that on the mainland trial sites the population has reached a balance between population increase ability and available food, so food is generally limited and hence foxes are much more likely to dig up buried baits.

In Tasmania the situation is a bit different from drier parts of New South Wales and Victoria where most of the reported buried bait fox poison trials have been conducted.  The differences are especially in the lack of free feed use prior to Foxoff provision in Tasmania, in the abundant alternative fresh road kill and fox naive wildlife near virtually all poisoning sites in Tasmania, and in the rapid putrefaction and 1080 degradation of the buried Foxoff bait in moist Tasmanian soil.

Given the total lack of any Tasmanian fox kill data, we really have to extrapolate from limited mainland Australia trials to just guess at the percentage of foxes killed by the 1080 poisoning for foxes to date.  It seems to me that it would be unrealistic to even expect it to be anywhere near, let alone above, 50% kill in any killing schedule, since there is no free feeding, a relatively unpalatable food (compared with fresh meat) is used, the food is buried, and abundant alternative fresh meat is usually available.  In nearly all peer reviewed scientific papers on fox control, buried baits have been found to be less attractive to foxes than surface baits, and Foxoff less attractive than fresh meat (e.g. see http://www.publish.csiro.au/view/journals/dsp_journal_fulltext.cfm?nid=144&f=WR10236) .

In principle the Tasmanian fox control situation is a bit like trying to kill off our junk food addicted enemies by providing them with hidden poison laced boiled tripe and brussel sprouts, half rotten and sprinkled with dirt! ( and with a McDonalds just down the street!)

Since the objective is to kill all foxes in Tasmania with a baiting program, it is not much point in just achieving a 25, 50, or even 90% kill rate, without follow up poisoning.  From a purely mathematical probability point of view, it would be necessary to repeat the initial poisoning effort 4 times to achieve near 95% kill if the chance of a kill from a single baiting programme was 50%.  Even 95% kill is not much use if a few animals remain to breed.  In principle this is rather like tossing a coin every month or so (representing a repeat poison event) and expecting it to fall heads (representing a fox kill) at least once.  Even if repeated 5 times the chance of a heads not falling at all is still significant at 3.1%. 

The Tasmanian fox eradication program is lucky to manage even a single repeat poisoning before foxes have had a chance to breed, and then only on selected sites assessed to be favoured fox habitat. To me it just seems illogical to totally rely on broadacre poisoning with relatively unpalatable buried 1080 baits, with a good chance that some target animals will remain, either because they became bait shy after eating some partially degraded bait, didn’t come across a poisoned bait, or were satiated with fresh road kill while poison bait was available. 

It is simply mathematically highly unlikely that even repeated fox poisoning in Tasmania will eradicate all foxes when the expected success from the poisoning technique is in the order of 50% or less for any poisoning event (or even if it is 70%!).  I would like to see better data on the expected kill rate from the exact same Tasmanian procedures by conducting trials on the mainland where foxes are known to exist?  The expected kill rate is of absolute critical importance of the whole operation of the fox eradication programme, yet no one has the foggiest notion of what it is under Tasmanian conditions and current procedures?  It would also be nice to get some advice from experts in mathematical probability theory, rather than just wildlife experts, and learn what they say about eradication prospects using current methods?

Regarding evidence for fox presence: - We know that an effort is made to find fox scats after each poisoning programme, but with only about 1 in 500 scats collected so far testing positive for fox DNA, and with most fox scats likely to be impossible to locate, or to be eaten or squashed by other animals before being found, there appears to be a fairly low chance of detecting evidence of more than just an occasional possible remaining fox.

As Dr Clive Marks pointed out (http://tasmaniantimes.com/index.php?/article/the-fox-that-wasnt-there/  ), there is something a bit weird about the scat DNA evidence to date, including the absence of data from the same or closely related foxes, from the locations of some scats, such as Bruny Island and from the absence of scats near food stations.  David Obendorf, Ian Rist and others in various Tasmanian Times articles and elsewhere have also provided a wealth of data documenting inadequacies in the reliability of other fox evidence in Tasmania. 

The time has surely arrived to try to detect foxes by other means, and to find evidence of their presence, apart from readily transportable scats, before blanketing vast areas with 1080.  The fox program has lots of night vision cameras, yet NOTHING that I can find has been published about what they have filmed digging up the 10%  +  of baits which are removed from their buried locations, and, obviously, no foxes have been caught on camera.

It is not too difficult to undertake an approximate cost-benefit analysis on this.  For example, the Landcare Research review includes data to show that $2.3 million was spent in 2008-09 on “operations” by the fox taskforce, to lay approximately 27,000 baits (at about one bait per 10 – 20 hectares). The cost represents $85 per bait, nearly all of it presumably labour and travel.  That is to say, it is enormously expensive to actually follow the official bureaucratic procedures, get to a poison site to lay the bait, and to return later to retrieve uneaten baits.  To actually dig a small hole to bury each bait probably takes just a couple of minutes or in the order of a dollar labour cost.  Since the operation’s branch represented 41% of total fox taskforce spending in 2008-09, then the monitoring, administration, and research sections supporting the poisoning operation raised the equivalent total cost to $207 per bait.

A question we can logically ask is – What can be done to get the unit bait cost down, enhance the likelihood that a fox will take a bait, more cheaply run the programme,  and more accurately truly monitor for fox presence? 

For starters, my view is that we should stop poisoning as a first offence strategy.  By using poison we have to avoid killing other animals as far as possible, and hence have to bury baits.  Poison also necessitates roughly double the average unit bait cost because of the requirement to return to retrieve uneaten baits.  By using fresh meat to attract any local foxes, food could be significantly more attractive than buried Foxoff, and local property owners, unemployed people or volunteers could avoid the expensive travel component necessitated by using city based fox taskforce workers to present the food to foxes. Using more palatable food could also include use of (say) live poultry in cages visible and audible to, but not reachable, by foxes (this might have problems getting Animal Ethics approval, but could be a welcome adventure for totally bored battery caged hens!)

By using fresh food (dead or alive!) it would probably also be feasible to reduce the bait density, to (say) one feed station per 50 hectares, reducing costs further.  Meat provided in this way would also be attractive to Tas devils, quolls, feral cats and some birds, so it would be necessary to provide it in feeders to avoid feeding non target animals as far as possible (it is pretty easy to design feeders to avoid feeding birds and devils.

Feral and stray cats are a bit more difficult to stop getting fresh meat from feeders that foxes can easily access, but such selective feeders are possible – note that the neglect of feral cat control in Tasmania is a whole new topic!! 

Eastern quolls and possums can access just about any feeder!).  A supply of sufficient attractive food in these feeders for a week or two could take place in cooler months from a single visit by an operator, thereby minimising costs.  Fresh pet meat is a cheap commodity, so would not represent a high cost.  After accustoming local meat eaters to these feeders for a sufficient period of time,  (e.g.  2 weeks – 2 months),  the presence of local foxes could readily be ascertained by a number of possible techniques, including local scat presence from their repeated visits, night vision filming, and voice recordings through the night.

Once the presence of an occasional fox visiting any feeder was confirmed, then the full arm of the fox taskforce law could descend to poison, trap or shoot the offender.  This procedure could potentially dramatically lower the cost of the fox eradication programme, enhance its effectiveness, eliminate the chance of non target animal poisoning, and provide real proof of the existence of foxes in Tasmania.

The apparent lack of serious recent attempts to film foxes and other animals digging up baits using the fox programme night vision cameras is concerning, as is the apparent lack of serious attempts to record fox calls using standard voice recording devices.  The programme has tens of cameras which seem to largely unused?  At least they could surely be routinely set up to film what happens to buried baits?  The science of night vision filming is developing in leaps and bounds, and modern cameras and powerful infrared light systems can pan in detail around areas of up to 50 hectares from a good vantage point right through the night (e.g. see .  http://www.dpipwe.tas.gov.au/inter.nsf/Attachments/LBUN-8BK6G8?open) .  Maybe the fox eradication programme should update from their toy cameras, or bring in experts, to have a chance of really filming a fox?  At least get some cameras capable of recording both video and audio right through the night, from a distance of at least 30 metres! Foxes are (apparently – I have never heard one around here at Maydena!!) quite vocal, especially at certain times of the year.  Surely it would be worth setting up some long term sound recording gear in likely fox habitat? 

2.  Uncertainty that Foxoff bait won’t kill native protected animals.

Fox Eradication Program factsheet 01 assures us that an average size 7 kg devil would need to eat at least 10 Foxoff baits within a 1 – 2 day period to receive a lethal dose.  The brochure “Targeted 1080 Baiting” has a table to show that an average Eastern quoll weighs 1.5 kg and would need 1.86 baits to be killed, whereas a Spotted- tailed quoll weighs 3.0 kg and would need to ingest 1.73 baits to be killed.  A 2.4 kg average possum would need 0.65 baits, a 25 kg dog 0.92 baits, and a 5 kg fox just 0.19 baits for a lethal dose.

This all sounds comforting, but unfortunately not all animals are average as regards either weight or poison susceptibility.  In addition the average weights for the various animals provided in the brochure table are, to be polite, seriously inaccurate, and don’t even differentiate between males and females!  For example the weight of an adult eastern quoll actually averages just 1.3 kg for males and 0.9 kg for females, (not 1.5 kg) (http://www.environment.gov.au/biodiversity/threatened/publications/pubs/quolls.pdf)  .  That alters the data to show that an average male Eastern quoll will be killed by 1.6 baits, but an average adult female by just 1.1 baits.

The data on animal susceptibility to 1080 all dates back to papers by J.C. McIlroy in the 1980’s The LD50 data usually presented refers to the 1080 dose required to kill 50 % of a population.  The variability in 1080 susceptibility for quolls is provided in his 1981 paper (http://www.publish.csiro.au/?act=view_file&file_id=WR95077.pdf)  For an LD05 value, the lethal dose of 3.73mg/kg for a LD50 changes to 3.18 for a dose to kill the most susceptible 5%, (a 17% change) and from 1.85 LD50 for Spotted-tailed quolls to 1.28 for a dose to kill the most susceptible 5%  (a 45% change).  This is saying that one standard Foxoff 1080 bait will easily kill the most susceptible adult eastern and spotted- tailed quolls. Belcher in 1989 studied the susceptibility of quolls to Foxoff and concluded that a single bait could kill them and that they could and would readily dig up and consume buried baits (http://www.publish.csiro.au/?act=view_file&file_id=WR95077.pdf)

Of course not all animals are adult, nor of average weight for their age.  Juvenile animals, partially or recently weaned, are especially likely to be killed by just a single bait portion.  This could include young devils, quolls, possums, (they readily develop a taste for meat!!) and possibly bandicoots, bettongs and potoroos.  Devils and quolls are already in serious decline in numbers in Tasmania, so this is a bit of a worry.

The aforementioned “Targeted 1080 Baiting” brochure says that “Monitoring trials have confirmed that 1080 fox baiting programs are not adversely impacting on native populations in Tasmania”. Sorry guys, but I don’t think so.  The old fox taskforce might have conducted some cursory trials to attempt to monitor populations before and after poisoning, but that approach is notoriously inaccurate. This is simply because nocturnal animals are incredibly difficult to count.  They scurry into bushes at the faintest sound of a person or sight of a spotlight.  They only way to get a proper idea of numbers killed is to check animals digging up baits and being killed.  Since no data has been forthcoming from filming buried baits being dug up, even that is apparently too difficult?

Please consider these matters and get back to me when convenient so that I can make an informed decision about whether to allow fox poisoning on our property.

Regards,

Ivo Edwards

Ivo Edwards has a 50 hectare property at Maydena.  He has developed and gained DPIPWE certification for various soft fabric humane animal traps to enable trapping as an economic alternative to 1080 poison for control of Bennett’s wallabies, Tasmanian pademelons, possums and feral cats.