European red fox and fox control
The European red fox is widespread in Australia and only absent from the tropical far-north.
The first were imported deliberately in 1845 (Abbott, 2011) for hunting and later also by farmers for rabbit control. However, those early releases have reportedly failed to establish.
In the south-west of WA they seem to have successfully established around the same time as rabbits. (Abbott, 2008)
First sightings in the Perth region were documented in 1931. (Abbott et al, 2014)
Because of their impact on agriculture, foxes were targeted for control actions as early as the 1880s. (Kirkwood et al, 2014)
The mainly British settlers had no concerns about the effect of foxes or cats on native fauna and our emphasis on native fauna conservation is a fairly modern concept. (Abbott et al, 2014)
Today foxes are a declared key threatening process under the EPBC Act as they constitute an ongoing threat to the survival of native species of the critical weight range, which are often the most vulnerable to decline and extinction. (Burbidge and Mckenzie, 1989)
They are considered to be opportunistic generalist predators and scavengers, however they can – similar to cats – also specialise successfully on particular prey. (Fleming et al, 2014)
In addition to direct predation, foxes can also affect native fauna through the spread of disease, such as round-worm, scabies and hydatid tapeworm. (Saunders et al, 2010)
Without doubt, foxes played a major role in the widespread decline and extinction of native, naïve mammal species (Abbott et al, 2014) and are a serious threat to ringtail possums.
This seems to be particularly true during winter when foxes were reported to be killing possums (common ringtails in this case) above and beyond their demand for food. (Short et al, 2002)
We struggle to effectively and efficiently manage those now entrenched species such as foxes and cats.
Today’s conservation methods seem to have largely failed (Hayward, 2011) and the management has shifted the emphasis from reducing predator numbers to mitigating the damage and reducing the impacts on native wildlife. (Krull et al, 2015)
The Australian Government’s Threatened Species Strategy however seems to be the exception from this rule as their ambitious plan is to cull 2 million feral cats by 2020. (Threatened Species Strategy, 2015: http://www.environment.gov.au/biodiversity/threatened/publications/threatened-species-strategy)
Control of foxes
In Western Australia Jack Kinnear pioneered fox control and the broad-scale control on conservation lands led to a dramatic recovery of many ‘critical weight range’ mammal populations. (Kinnear et al, 1988, Kinnear et al, 1998)
According to the IUCN Red List of 2012 which was released at the Rio Earth Summit some species in the south-west of WA have however begun declining again after the initial impressive recovery (Wayne et al, 2013). The causes are many and habitat issues such as degradation, fragmentation, drought and other climate change related problems seem at the forefront.
A sustained recovery of the western ringtail possum for instance seems very unlikely if a broad-scale fox poisoning program is the main initiative.
A major issue is also the lack of monitoring. Neither the response of fox populations to baiting nor the recovery of vulnerable species in the baited areas is usually monitored adequately. Success stories after Western Shield baiting are often unsupported by monitoring data. (De Tores et al, 2004)
Poison baiting of foxes is the most widespread method of fox control and considered most cost effective. (van Polanen Petel et al, 2001)
Gastrolobium, a genus of flowering plants native to the south west of WA, produce a compound commonly known as 1080 (sodium fluoro acetate). The native wildlife particularly in WA co-evolved with these plants and is highly tolerant to the compound while introduced species such as foxes or cats are very sensitive to it. It seemed to provide the ‘silver bullet’ to killing introduced predators while not harming native wildlife.
Consumption of as little as 3 mg of 1080 is lethal to foxes and cats.
The toxin is currently the only registered and approved poison for fox control in Australia and available to landowners (regulated by a permit system). (Mallick et al, 2016)
Unfortunately 1080 also proved lethal to several native mammals, reptiles and birds and of course to our pet dogs and cats.
This risk to non-target species, concerns that it is inhumane as the average time until death is 6 hours and that there is no antidote available for accidental poisoning, have made it very controversial indeed. (Mallick et al, 2016)
1080 can either be used in meat bait or in eggs that are then buried.
Burying either bait might seem safer but in trials bandicoots, common brushtail possums, brush-tailed phascogale and reptiles were all observed digging them up. While those mammals are very tolerant and would need to consume a high number of baits to be harmed, reptiles are not.
For the protection of reptiles it seems safer to hang bait up in the bush well out of their reach.
Newer research (Dundas et al, 2014) has also shown that joeys learned from their brushtail possum mothers to take bait and even though the adult has high tolerance to 1080 their pouch young have not. Even if pouch young do not consume the bait themselves, they can die after ingesting it through their mother’s milk.
As the likelihood of finding poisoned carcasses is low, there is still a risk that through this learned behaviour of taking bait some younger brushtail possums would actually eat enough of the baits for a lethal dose.
Equally the analysis of efficacy of a baiting program is difficult without recovery of carcasses. As documented in Western Australia, surface laid baits not consumed quickly by the target species are frequently taken by birds such as raptors, ravens or magpies. If they then were eaten by a native carnivore or scavenging bird which is then potentially killed through secondary poisoning the flow-on effect can be quite significant. Toxicity of 1080 in carcasses can persist for several weeks. (Mallick et al, 2016)
Departmental broad-scale distribution of bait is usually done from aircraft. However, that means some bait will land in inaccessible terrain and potentially not be discovered for weeks when toxicity has declined to sub-lethal levels. Bait also degrades in heavy rain.
It might be necessary to deploy bait manually to improve bait encounter and consumption rates or in very high quantities. 5-10 baits per square km or at least one bait per estimated fox is recommended. (Bengsen, 2014) This would however increase the risk for non-target species again. Ground baiting is currently mainly limited to small reserves with conservation significance. (Dundas et al, 2014)
A quick uptake and consumption of the bait is also unlikely if alternative food sources (live prey) are plentiful. If bait is taken even though there are lots of rabbits, it is most likely cached.
Cached baits may again become sub-lethal if stored for long. (Thomson and Kok, 2002)
Bengsen estimates that fresh meat baits can only be expected to be lethal for up to a week (Bengsen, 2014), which would be in contradiction to the claim that carcasses can stay toxic for several weeks.
Sub-lethal doses in late-discovered or cached baits can lead to bait aversion. The fox remembers the pain after eating bait and will not repeat this experience.
Repeat ingestions of sub-lethal doses can also increase tolerance to the poison in the future. Rabbits reportedly already show signs of increased tolerance to poisons. (Twigg et al, 2002)
In general, the most palatable bait is consumed quickest and deep-fried liver has been reported as the most thought-after.
In the same trial, Foxoff – the most commonly used meat bait – was the one cached most often. (Mallick et al, 2016)
Potentially two other toxins can also be used for fox control: para-aminopropiophenone (PAPP) and sodium cyanide (NaCN).
Both appear more humane as cyanide acts within minutes and PAPP seems relatively free of severe pain. Another advantage is that those toxins do not leave persistent residues. (Mallick et al, 2016)
Cyanide would however kill all vertebrates with a single dose and is therefore restricted to research projects.
PAPP is in the scientific trial phase. The standard amount of PAPP (226 mg) would not only be lethal to foxes and cats but also to domestic animals and native wildlife.
There is an antidote commercially available but it needs to be applied within 1 and a half hours. (Mallick et al, 2016) The risk to non-target species can however be severely lowered if the toxin is delivered via ejector.
Ejectors are buried in the ground so that only a baited lure containing a sealed capsule filled with PAPP is exposed. If a stronger animal such as a fox tries to remove the lure, a spring loaded piston will inject the poison into its mouth.
Smaller animals, reptiles or birds would be safe as they should not be able to trigger the ejector; however adult brushtail possums would probably be strong enough and die from the toxin.
As PAPP degrades fast and as it is injected straight into the mouth, only little toxin would be in the killed animal's body tissue which would lower the risk of secondary poisoning for scavengers. (Mallick et al, 2016) There is also the option to deliver 1080 via ejector.
However, no matter which poison, the use of ejectors is most likely limited in scale.
A still popular control option for foxes- particularly with the public - is shooting as this is regarded as the most humane method. However, it is neither cost-effective nor a strategic method for significantly reducing populations of foxes. (Fleming et al, 2014)
Sporting shooters who might hunt with spotlights or dogs (e.g. Red Card for Red Fox Program) put emphasis on reducing fox numbers but without also monitoring control efficiency; however, they have the advantage of not endangering domestic animals (Kirkwood et al, 2014).
Shooting is also a good option to target invading individuals.
The use of cage traps seems mainly suitable for urban or peri-urban areas where poisoning or shooting is problematic or impossible. Again, it seems to be limited to removing troublesome individuals and will not have much effect at reducing population levels.
The effectiveness (or else) of leg-hold traps so far seems undocumented.
Den fumigation can also be effective, particularly in the breeding season; however, it is labour intensive and expensive and another method that would not target foxes at population level.
Guardian animals such as Maremma dogs have been used successfully to protect for instance lambs from foxes. The effectiveness under Australian conditions has not been scientifically assessed though (Fleming et al, 2014) and whether the dogs can be trained to bond with wildlife and in particular arboreal wildlife like ringtail possums is doubtful. As they will not kill the fox, the problem might also just be chased to the neighbouring property.
All attempts at fox control can be hindered by their high fecundity and their ability to travel tens of kilometres in a single night. (Kirkwood et al, 2014)
It seems that the use of several control methods at the same time increases the chance of success. However, foxes are clever and adapt with time.
The WA Western Shield Program has demonstrated that a sustained long term reduction of foxes and therefore their impact on native wildlife can be achieved.
However, aerial baiting needs to be conducted over a large area and repeated frequently to counter dispersal and recruitment. (Fleming et al, 1996) Patchy distribution of bait will reduce the effectiveness as new foxes from unbaited areas will fill the available vacancies fast. (Mallick et al, 2016)
Resources and time are limited and efforts seem to be decreasing or are redirected towards cat eradication programs.
Baiting through private land owners is unlikely to achieve significant results as the baited area is usually small, the number of baits is low and there is no or poor coordination between neighbouring properties. (Bengsen, 2014)
Baiting programs need departmental guidance, have to be financially supported and coordinated amongst neighbouring landowners for best outcomes. Unfortunately baiting outside the conservation estate has very low priority and even when an incursion of foxes is triggered by departmental actions (control burn) there is no support available.
It is estimated that fox control programs need to achieve an annual population reduction of 65% or the population recovery can negate any gains quickly. (Bengsen, 2014)
How well bait is taken by foxes seems to vary widely and for a myriad of reasons. Numbers in the literature span from 50% at best to 1% at worst. (Towerton et al, 2016) Reliable figures would depend on monitoring the decline of foxes and the recovery of their prey which so far has rarely been done. Sandpits were used to monitor whether foxes took the bait, however foot prints of a fox are no definite proof that the fox actually ate the bait. (Towerton et al, 2016)
The use of cameras to observe which species took the bait and how quickly it was detected and taken is becoming increasingly popular. (Dundas et al, 2014) Large scale and long-term camera monitoring could then also establish whether the fox abundance decreases and whether there is a noticeable increase in prey species abundance.
Fox activity is usually highest in agricultural areas, lowest in forests. (Towerton et al, 2011)
They prefer tracks, roads and fire breaks particularly in areas with dense vegetation. (Towerton et al, 2016)
Trials in the south-western Jarrah Forest had good bait uptake in agricultural areas, while the uptake by non-target species was particularly high in forest.
Foxes were observed near the bait and some even sniffed it but did not take it which is also our experience.
In this study 99% of bait was taken by non-target species – mainly common brushtail possum, quenda, brush wallaby, chuditch, quokka, black rat, bobtail lizard, magpie and raven. (Dundas et al, 2014)
The jury is still out whether the red fox or the feral cat is the most destructive introduced predator on mainland Australia, however foxes definitely pose an ongoing threat.
