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).
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).
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 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.