Is it too late to bring the red fox under control?

The red fox is significantly implicated in wiping out native mammals, but there are some promising methods for reducing its impact. Harley Kingston

The red fox may be the most destructive species ever introduced to Australia. For a start, it carries most of the blame for Australia’s appalling record of recent mammal extinctions.

Since European settlement, mainland Australia has lost at least 20 mammal species, far more than any other country over the same time period. Mostly these were bandicoots, bilbies, rat-kangaroos, quolls and hare-wallabies, along with relatively large rodents. Over vast areas of southern mainland Australia there are simply none of these medium-sized native mammals left - just seemingly limitless numbers of foxes and rabbits.

Did the fox act alone to cause these extinctions, or did it have help? Maybe other pressures - like competition from rabbits, changed fire regimes, or unknown diseases - were also important. The evidence, however, points consistently to foxes as the dominant cause. If other factors contributed it was probably by amplifying the predation pressure from foxes on native prey species. The European rabbit, for example, had an important subsidiary role by boosting fox numbers, and keeping them high even as native prey crashed to extinction.

The fox is also a significant pest to agriculture, mainly through preying on lambs and poultry. It can spread disease to domestic animals, and would be a carrier of rabies if that disease ever got into Australia (which is a distinct possibility). The combined environmental and agricultural impacts of foxes, and the effort expended on attempts to reduce that impact, probably costs Australia more than $200 million each year.

But it could all have been so different. A brilliant piece of historical research by Ian Abbott shows how difficult it was to introduce the fox to Australia. Victorian settlers, who were keen to indulge the “noble sport of fox-hunting”, released foxes on many occasions, beginning in the 1840s. Some early releases were evidently quite serious attempts to establish wild populations, such as a liberation of a group of at least six foxes in the Dandenong Ranges in 1864.

Released animals were rarely, if ever, seen again. They may have been killed by hunters or dingoes, or they might have taken poison baits that were laid for dingoes and stray dogs. In any case, they did not establish viable populations.

It was not until about 1874 that a fox population finally took off, on the Werribee Park property of the wealthy Chirnside family. From that point the fox was unstoppable. Despite all attempts at control it swept like an avenging fire through all of the southern half of Australia in just a few decades.

This history nicely illustrates an important biological principle. Small, newly introduced populations face a high intrinsic likelihood of going extinct. The small numbers of animals in such populations might be hard to find, but even poorly targeted control efforts can be useful if they increase those individuals’ risk of death, and therefore make it even more likely that the population will go extinct.

This history may now be repeating in Tasmania where an illegal release of several foxes in about 1998 has evidently resulted in a widely dispersed but extremely low-density fox population.

The Tasmanian State Government is attempting to push this population towards extinction using broad-scale poison baiting. This is controversial, but is the most sensible response to the risk that foxes will do to the Tasmanian environment what they have already done to mainland Australia.

As with any other well-established invasive species, it is very hard to turn back the clock and reduce the impact of foxes. Trapping and shooting generally have little effect on population size unless they are done intensively in well-defined areas where rates of re-invasion are low. Bounty schemes set up to encourage broad-scale fox removal by shooters, such as the program recently established by the Victorian State Government, are likely to be ineffective and wasteful.

There are four control options that can produce sustained reductions of fox impact.

First, poison baiting using 1080 can give good results, because foxes readily take poison baits. There is a particular advantage in the use of 1080 to protect wildlife from fox predation in Australia, because while foxes are highly susceptible to this toxin, native Australian mammals are much less so because it occurs naturally in some Australian plants. A drawback is that reduction in fox abundance can result in increased feral cats (which are also susceptible to 1080 but generally do not take baits), because foxes aggressively suppress cats. For some prey species, cats are just as significant a threat as foxes, or more so.

Fencing can be used to exclude foxes from high-value areas such as nature reserves, although the investment needed to protect large areas in this way is huge.

Livestock guardian dogs, such as the maremma sheepdog, have proved their worth in protecting livestock from many species of predators, including foxes. Guardian dogs have even been used to keep foxes away from seabird colonies in southern Victoria.

Finally, in some situations dingoes can reduce populations of both foxes and feral cats. They do this partly by hunting and killing them. Intriguingly, dingoes have been recorded killing foxes and cats but not eating their victims, as if the killing was motivated by simple malice. This is a good thing, because it means that foxes and cats fear and avoid dingoes, so that habitats in which dingoes are active can serve as refuges for prey species that are especially vulnerable to both foxes and cats.