The fox that wasn’t there?

The “precautionary principle” demands no actual proof to justify an action, but only a belief that we can’t afford not to act. It sits uneasily with the scientific method, as it can be born of faith and good intentions rather than knowledge sought through testing assumptions and most importantly revision of a hypothesis when it is found wanting. The precautionary principle can be a path to the dark side for a scientist and it is indeed easy to go there through fear alone.

Yet there have been real foxes introduced to Tasmania. The first Burnie fox sailed from Melbourne’s Webb Dock to Burnie in May 1998 and its arrival is undisputed given the physical evidence and video footage.

From 1990 until 1994 I had studied and radio-tracked foxes at Webb Dock so I knew the site and the breeding biology of these foxes quite well. Foxes use seasonal changes in day length to time their reproduction, breeding only once a year and have a very predictable duration of pregnancy. So, I can say with confidence that if the first Burnie fox happened to female, short of a vulpine equivalent of the Immaculate Conception, it could not have contributed to a Tasmanian population of foxes unless others were already there, waiting dockside in Burnie.

Yet in 2003 when the original Burnie fox would have almost certainly been long dead, another apparently road killed female fox turned up very near the same Burnie Port and another fox was reported to have leaped from a shipping container some 100km away in April or May 2001 - the chances of it being pregnant if it came from Webb Dock also being zero. Now, here you might think, two foxes could have met and begun an established population, despite the distance and two-year time gap between their arrivals - but an autopsy showed that the new Burnie fox had never reproduced. It died a spinster.

Strangely it would appear that Webb Dock foxes have a unique attraction for the Apple Isle and this in itself is mysterious. I have long pondered if perhaps the criminal investigation into foxes arriving in Tasmania began on the wrong side of Bass Strait. Yet even though these foxes arrived at different times and places, there is no convincing evidence that they could have been part of a founding population. True, these are foxes we know of and those who favour the “precautionary principle” may never be satisfied with those things we do not know of.

Strangely there has never been unequivocal documented evidence of a fox breeding den in Burnie. Yet after studying foxes in Australian cities for some eight years, I know that breeding dens are quite easy to find, even at low density. After some six breeding seasons at least, if you can’t find dens they are almost certainly not there or the people looking for them are incompetent. Take your pick.

In fact, not one breeding den has been found in Tasmania. This would be irrefutable evidence after all for if would be next to impossible to fake one.

There are dead foxes that have popped up in Tasmania. While the media reports them, unfortunately there has been little appropriate scepticism when it has been most needed. Vital pieces of physical evidence come to light belatedly, anonymously or, as it has been later found, in suspicious circumstances. Some have turned out to be blatant frauds or cases where fraud could have been easily perpetrated. But none amount to confirmation that a breeding population of foxes is established in Tasmania. We remain marooned in the realm of belief - one way or the other, still looking for irrefutable evidence.

The most convincing evidence that foxes exist in Tasmania comes from using a relatively new technique that extracts DNA found in faeces (scats) confirming they came from a fox with a high degree of reliability - it was a technique developed at Monash University and tested in the field by my team. The idea is elegant; if you find a fox scat it is likely to contain traces of that fox’s DNA. It’s evidence that a known fox has been there and you can count the number of individuals from collecting scats marked with their unique DNA. Straightforward, but only if you can be absolutely confident that your fox scats were not planted, contaminated, mislabelled or subject to unknown errors in analysis.

As foxes can defecate some eight times a day and are territorial, that’s an awful lot of fox crap in one discrete home range waiting to be found after a few days, especially if you have a trained dog to help you. In fact, because foxes are strongly territorial, you would expect to find large clusters of scats in one area. And that’s just the problem. Of the 56 fox scats so far identified as “fox” in Tasmania (because not all have been analysed for individual DNA), they do not come from within clusters of positive fox scats.

Of the 15 identified individuals, no two scats have come from the same fox.

Some people suggested that Tasmanian foxes might not be territorial and could behave differently from their mainland counterparts. But if we have a breeding population of foxes established, they must be territorial for a good period of time, otherwise it is simply impossible that they can reproduce after establishing a breeding den - which they must do.