Making a killing: where to for fox and cat control?

A famous number in Australia’s history is 10.99%, but if you asked what it meant very few people would be able to tell you. Currently, 10.99% of Australia’s mammalian species have become extinct since European colonisation - a new world record. That’s a whopping 30 of 273 mammal species gone forever. These were species that represented what it meant to be quintessentially Australian and they will never return. If that doesn’t bring a tear to the eye or raise alarm bells, then nothing will.

The loss of mammals in Australia is due to various factors. Nothing in ecology is ever simple, but the main reasons tend to be habitat loss and modification, coupled with increased predation pressure from introduced species. The feral cat (Felis catus) and the invasive red fox (Vulpes vulpes) are two such predators that have decimated native species in Australia. Both introduced in the 1800s, they tend to favour smaller sized animals, and they have a very different diet to our other two extant, top order predators: the dingo (Canis lupus dingo) and the Tasmanian devil (Sarcophilus harrisii).

A feral cat carrying its dinner, a critical weight range mammal. (Image: Billy Geary)

A feral cat carrying its dinner, a critical weight range mammal. (Image: Billy Geary)

So with the demise of native predators such as the thylacine (Thylacinus cynocephalus), Tasmanian devil, eastern quoll (Dasyurus viverrinus), western quoll (Dasyurus geoffroii), northern quoll (Dasyurus hallucatus) and tiger quoll (Dasyurus maculatus), a changing of the guard has occurred that feral cats and foxes have taken advantage of. But how do they stack up against our native species? Since their introduction, both cats and foxes have impacted the land by putting additional predation pressure on many native species, especially mammals that fall into the critical weight range (CWR) of 35g to 3.5kg.

The widespread reduction of mammals in the CWR has led to a huge spate of ecological issues. Due to the nature of trophic levels, mammals within the CWR would rarely have been subjected to predation pressure from top order predators (although both foxes and cats are classified as mesopredators, in many systems void of dingoes they are the apex predators).

Foxes are distributed widely across Australia. Image: Billy Geary

Foxes are distributed widely across Australia. Image: Billy Geary

Such a dramatic reduction in small and medium-sized mammal species has potentially led to a suite of ecological services being lost. Species such as the greater bilby (Macrotis lagotis) and burrowing bettong (Bettongia lesueur) can promote the germination of native plants, as their foraging digs collect more water and seeds compared to rabbits. They also increase soil turnover, adding much needed nutrients into the system by promoting breakdown of leaf litter which may also reduce fire fuel loads.  Some of our most important species including the eastern bettong (Bettongia gaimardi gaimardi), eastern hare-wallaby (Lagorchestes leporides) and desert bandicoot (Perameles eremiana) have disappeared due to predation, and the ecological processes that they once provided are forever gone.

Subsequently, the question at the forefront of many ecologists’ minds is where to next, and how can we best control feral cats and foxes? For years, the go-to method has been shooting and poison-baiting. Although these two methods have merit in small areas when they are sustained over time, they are not a one-size-fits-all approach in a continental context. In some cases, casual baiting and shooting may lead to increases in feral cat and fox numbers due to the landscape being opened up, allowing other invasive predators to move into the vacant territory.

In more recent times, the case for rewilding our native predators, like dingoes and Tasmanian devils, has been put forward as a method for controlling the feral cats and foxes for us. Rewilding, once native predators are established, may also be more cost-effective in some cases compared to baiting, with widespread benefits provided for the multitude of species that invasive predators eat and kill. With species within the CWR released from the risk of being killed by foxes and cats, their numbers should increase in suitable habitat.

There is of course the argument that with an increase in native predators, specifically the dingo, farmers will lose more livestock due to predation. This may only be partly true. There is an emerging body of evidence suggesting that farmers and dingoes can exist in a mutually beneficial partnership. By not killing dingoes, the species’ pack structure and bonds remain strong, and they hunt and kill prey together, focusing largely on macropods. When they are killed periodically through shooting and poison-baiting their pack structure can be broken down, sometimes leading to individual dingoes targeting livestock. By having stable dingo packs in the farming landscape, overabundant herbivores such as kangaroos (Macropus sp), as well as feral goats (Capre hircus), feral donkeys (Equus asinus) and feral horses (Equus caballus) are controlled. This allows for more plant biomass to grow and be used for cattle. Researchers have even calculated that farmers may be $0.83 better off per hectare by not controlling dingoes, due to the associated reduction in grazing by overabundant herbivores.

With the future of so many of Australia’s unique species under threat of feral cats and foxes, the time for discussion and action is now. A whole host of species are depending on us to act quickly and decisively, or we risk adding to our already dismal extinction list. Lethal control techniques are just one method in the invasive predator control toolkit. Therefore, we must continue to develop new ways to think of not only how to reduce the effects of feral cats and foxes, but also how to use our natural predators to improve our biodiversity.


Grant Linley

Grant is an ecologist interested in Australia's flora and fauna. He has experience researching, trapping, tracking, identifying and handling different Australian species. Whilst experienced in terrestrial Australian ecology, he has also conducted research in Borneo and South Africa. Grant's interests centre on preserving and reintroducing extant and extinct Australian species as well as using natural predators to control mesopredators.

No place like home: the case for rewilding the Tasmanian devil

Tassie Devils are amazing creatures, but their situation is dire. Australia’s largest marsupial carnivore is one of the few species on Earth whose major plight isn’t caused by humans. Rather, it is caused by something much more insidious – evolution.

Evolution, in combination with low genetic diversity caused by a series of historical population crashes, has conjured up a horrible illness called the Devil Facial Tumour Disease or DFTD. Originating from the mutated cell of a single devil, DFTD causes large, cancerous growths to form in the animal’s mouth, preventing feeding and often causing death due to starvation. It’s a horrible way to go.

The devastating facial tumour disease. Photo source: Menna Jones / Wikimedia Commons

The devastating facial tumour disease.
Photo source: Menna Jones / Wikimedia Commons

However, what is most frightening about this tumour is that it is contagious - among devils, not people. Devils often feed together on the same carcass, or even fight over it. This causes the cancer cells to move from devil to devil through saliva in their food as they argue over the last scraps. It’s this aggressive, transmissible quality that has seen the cancer spread like wildfire from one single individual to nearly the entire Tasmanian population, from east to west. The result is a species teetering on the brink of extinction. 

Despite a lot of work being done on creating vaccines for DFTD, maintaining captive breeding populations and, recently, establishing a wild population on Maria Island free of DFTD, this may not be enough. A new, potentially game changing proposal has also been gaining momentum: to re-establish or rewild disease-free populations of the Tassie Devil to mainland Australia. This kind of innovative thinking could be the saviour of the species. 

So, what is the case for rewilding the Tasmanian Devil?  

Is it time for the Tasmanian devil to return to its former home? Photo: SJ Bennett

Is it time for the Tasmanian devil to return to its former home? Photo: SJ Bennett

1. Devils used to be here, anyway

Fossils show that the devil coexisted with other native mammals on the mainland up until fairly recently (5000 to 400 years ago, depending on the accuracy of the dating). In fact, Devils once lived far up into the north of the country. Why did they disappear? No one knows for sure, but hunting by Indigenous Australians and the introduction of the dingo may have had something to do with it. 

Because of this, we can be fairly sure that devils, if brought back to mainland Australia, wouldn’t be another cane toad or European carp disaster, eating everything in its path. Also, Devils have lived with an enormous range of bite-sized marsupials in Tasmania, much more than mainland Australia. This suggests that Devils are capable of coexisting with smaller prey species without hunting them to extinction. 

Recent research using species distribution models has shown that the prevailing climate is just right for devils across south eastern Australia. According to this modelling, places like Wilson's Promontory and Barrington Tops might be perfect homes for Devils.

The former range of the Tasmanian devil. Source: Rewilding Australia

The former range of the Tasmanian devil.
Source: Rewilding Australia

The potential climatic range of the Tasmanian devil. Source: based on  Hunter et al. (2015)

The potential climatic range of the Tasmanian devil. Source: based on Hunter et al. (2015)

2. Devils need More insurance populations

The species needs insurance populations that are disease-free, simply so that the devil’s survival is ensured. Captive breeding programs have been the saviours of species many times over, but they can sometimes struggle to emulate the experiences of living in the wild. As the saying goes; ‘there’s no place like home.’ A wild, disease-free population will maintain the instincts and behaviours required for survival, as well as providing another source of genetic diversity for the species. These two things will be vital when the time comes to help build the Tasmanian population back up to historical levels.

Indeed, there’s evidence that Devil introductions or reintroductions can occur successfully.  A couple of years ago, a population of devils was established on Maria Island on the east coast of Tasmania. This is the first time devils have existed on the island and there’s every indication that individuals cope with moving houses, with little harm on existing native wildlife. 

Are captive populations enough to keep the devil going? Photo: Jay Town

Are captive populations enough to keep the devil going? Photo: Jay Town

3. Devils may help balance our ecosystems

Where they persist, Tasmanian devils are apex predators. They are typically quite timid and prefer carrion, but their mere presence in the environment can scare smaller species away, creating a ‘landscape of fear.’ Not dissimilar to the neighbours cat being terrified of your
otherwise lovely Jack Russell. They are capable of keeping grazing animals like rabbits down, allowing vegetation to do well. 

Perhaps more importantly, recent research has suggested that devils can also disrupt feral cat behaviour. This may mean that the devil could shield endangered prey species from predation, which has immense conservation benefit. Some recent computer modeling also supports this suggestion, even predicting that devils may scare foxes away, too.

Could the Tasmanian devil fill the same ecological role as the dingo, as explained here? Made by Daniel Hunter (Hunted Films) 

4. There's scientific and public support for a trial 

A recent public survey by Rewilding Australia found that, of over 400 respondents, 85% supported a trial reintroduction of Tasmanian devils to the mainland, whilst another 13% suggested they could be persuaded if presented with enough evidence. There's also strong scientific backing for a trial to occur in Victoria, with scientists from Deakin University, University of NSW and the University of Tasmania in support.  

Any proposed reintroduction will need to be a well thought out and planned exercise. Returning the Tasmanian devil to its original home, such as Wilson's Promontory, has real potential to not only help secure a species, but also provide greater benefits on an ecosystem scale. There will be tensions that need to be addressed, but ultimately the pros outweigh the cons to the point where reintroducing the Devil needs to be considered, such as the proposal outlined by Zoos Victoria in their Conservation Master Plan. With a dying population due to DFTD, proactive and innovative solutions are required. So, perhaps it’s time to welcome the devil back to its ancient home and recreate a thriving ecosystem. 

Cover image supplied by Catherine Cavallo

Billy Geary
Billy is the Science & Conservation Editor at Wild Melbourne. He is a wildlife ecologist interested in predator-prey interactions and invasive species management.

You can find him on Twitter: @billy_geary