predators

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.


download.png

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.

The Extinction Of The Thylacine: A Cautionary Account

The thylacine sounds like something out of a children’s book: it was an animal with the body of a dog, a kangaroo’s tail, a pouch, and stripes from its shoulders to its tail. It is said to have had an awkward gait and was rarely seen to move quickly, yet it was a proficient carnivore, preying upon a variety of marsupials under the cover of darkness. Thylacinus cynocephalus (dog-headed pouch-dog), also known by its more common name the Tasmanian tiger, was once an apex predator throughout mainland Australia, Tasmania and New Guinea.

This unusual creature is an excellent example of convergent evolution, which occurs when two unrelated species are put under similar evolutionary pressures and exist in a similar ecological role, producing two species that possess similar features. In other words, similar problems produce similar solutions. Although the thylacine superficially resembled members of the family Canidae (such as wolves and dingoes) with its sharp teeth, raised heels, muscular jaws and dog-like body form, its marsupial pouch, kangaroo-like tail and relatively short legs point towards the fact that this species is only distantly related to its canine doppelgangers. It was the only extant member of the family Thylacinidae, its closest relatives being the Tasmanian devil and the numbat.

One of the few photographs taken of the last thylacine, a resident of Hobart Zoo.  Photo courtesy of Australian Museum.

One of the few photographs taken of the last thylacine, a resident of Hobart Zoo. Photo courtesy of Australian Museum.

The modern thylacine evolved around four million years ago, and although it had previously been found throughout continental Australia, it became extinct on the mainland at least two thousand years ago. The mainland extinction was possibly due to competition with dingoes. However, this is arguably related to the two species’ opposing lifestyles: dingoes typically hunt during the day, whilst thylacines were mostly nocturnal.

The thylacine's last stronghold was the island of Tasmania, but the arrival of Europeans to Tasmania in 1803 spelled the beginning of the end for the marsupial carnivore. When sheep were introduced to the island in 1824, the thylacine began to gain notoriety among farmers as the culprit responsible for attacks on livestock. While Tasmanian tigers would have had some effect on the growing population of sheep on the island, their impact was greatly exaggerated. One infamous photo of a Tasmanian tiger with a chicken in its mouth is now thought to have been staged, with the photographer likely to have created the scene by placing a dead chicken in the mouth of a taxidermied thylacine. Due to the hype surrounding its apparent effect on livestock, a bounty was placed on the thylacine, with the Tasmanian government paying one pound per head. Between 1888 and 1909, over 2184 bounties were paid out to farmers and hunters alike.

The infamous image of a thylacine with a chicken in its mouth - most likely staged.  Photo courtesy of Australian Geographic.

The infamous image of a thylacine with a chicken in its mouth - most likely staged. Photo courtesy of Australian Geographic.

By this time, hunting had taken its toll on the species. Thylacine sightings became infrequent, and zoos around the world sought after the strange animal. Still, the extermination undertaken by farmers and hunters continued. The last known wild thylacine was shot by farmer Wilf Batty in 1930, and then finally, the last captive thylacine died in Hobart Zoo on the 7th of September, 1936. Only then, once the last known Tasmanian tiger had perished, was it placed on the threatened species list. Ultimately, having not been seen in the wild for fifty years, the thylacine was declared extinct in 1986. In addition to the hunting pressure brought about by humans, the demise of the thylacine has been attributed to habitat loss, competition with dingoes and introduced wild dogs, and the concurrent demise of its prey species.

The extinction of this mysterious marsupial is commemorated every year on Threatened Species Day, which falls on the 7th of September: the day that the last known Tasmanian tiger died. Now more than ever is the loss of the thylacine relevant to the struggles we face in trying to combat the extinction of our native animals, and should serve as a reminder not to take our unique wildlife for granted. Victoria is home to an array of species that not only fascinate and inspire, but also play an integral role in their respective ecosystems. Personally, I would have treasured a sighting of a Tasmanian tiger in its natural environment, but sadly this is something that I and countless others will never experience. We need to rally behind our native wildlife today so that as we grow old, we will not look back and wish we had done more.

Australia has the worst mammalian extinction rate of any country in the world, having lost 29 species over the past two centuries. I wonder, what is in store for the next 200 years?

A combination of all known video footage of the thylacine. Courtesy of The Thylacine Museum.

Banner image courtesy of Joseph Gleeson (painter)

Big Desert Adventures: Part Three

Since settlement times, Victoria’s Mallee region has captured the public imagination. Upon digging up old newspaper articles documenting early expeditions to the region, tales of ‘tiger cats’ hell bent on attacking people, and medium-sized marsupials (e.g. bettongs and bandicoots) in apparent plague proportions, are common. Over time, these bush yarns have only enhanced the region’s mystique and reputation as somewhat of a wild frontier. 

Once upon a time quolls and dingoes appeared to rule the Big Desert/Wyperfeld region from the top of the food web. It’s now a slightly different storey, but no less intriguing.  

The third instalment of my Big Desert Adventures blog is being hosted on Euan Ritchie's website. To find out what my camera traps have revealed so far, read on here.


Big Desert Adventures: Part Two

I’ve just returned from my first foray into Victoria’s spectacular Big Desert, and it was every bit as successful as hoped. Currently, there are 35 predator cameras and 35 prey cameras deployed across 35 sites within the Big Desert Wilderness Park, Big Desert State Forest and the Wyperfeld National Park. It really is a beautiful region, hosting a range of ecosystems not seen anywhere else in Victoria.

A picturesque Big Desert sunrise. Photo: William Geary

A picturesque Big Desert sunrise. Photo: William Geary

With any luck, there’ll be a nice array of critters dancing in front of my cameras as you read this. Specifically, at each location I’m targeting Dingoes, Red Foxes and Feral Cats with the predator cameras and a bunch of small mammals (including the Silky Desert Mouse, Mitchells Hopping Mouse and the House Mouse) with the prey cameras. Why these animals though? Well, have a read of my last article describing the background of my project in a little more detail.

You might be wondering what these cameras I’m speaking of look like, so here’s some examples below. The movement of heat (i.e. a body) across a detection zone triggers the cameras, taking video or photos in response. However, that’s where the similarities end; the predator cameras are outward facing, in order to observe larger animals. On the other hand, the prey cameras face downwards as this aids the identification of many small mammal species. Without the help of camera traps, there are quite a few species I wouldn’t even be able to detect, making them an essential tool for any wildlife ecologist. 

The downward facing prey camera, complete with delicious peanut buttery bait. Photo: William Geary. 

The downward facing prey camera, complete with delicious peanut buttery bait. Photo: William Geary. 

The outward facing predator camera in some early successional heathland. Photo: William Geary

The outward facing predator camera in some early successional heathland. Photo: William Geary

In addition, I surveyed for predator scats at each site, collecting nearly 100 samples across nearly 90km worth of transects. Helpfully, Canid and fox scats are generally very easy to spot as they tend to be placed quite prominently in order to mark territory. These will give me another insight into what habitats the local predators are using most. We’ll also be sending the scats off for diet analysis to find out just what’s on the menu in the Big Desert for our furry carnivores.

At our last site we got a true indication of just how merciless fire can be in the mallee (see the photo below). With absolutely nothing left, save for one or two coppicing Eucalypts, one really gets an idea of what the phrase ‘resetting successional trajectory to year zero’ means. Or, in layman’s terms, clearing the ecological slate and starting from scratch. There are very few places in Victoria where succession can be viewed as vividly as in the mallee.

Fire can be absolutely devastating in the Mallee, leaving very little behind. Photo: William Geary

Fire can be absolutely devastating in the Mallee, leaving very little behind. Photo: William Geary

Having traversed a myriad of sandy 4WD tracks, both in the car and on foot, one really gets an appreciation of just how vast and untouched the region is. The sensation of looking out from the top of a dune, with not a single man-made feature in sight is something pretty special. This was compounded at one point with three or four Wedge Tailed Eagles flying overhead whilst gazing off into the distance. Importantly, the Big Desert’s vastness shouldn’t be mistaken for emptiness, with the place absolutely crawling with wildlife.

The vast landscape of the Big Desert. Photo: William Geary

The vast landscape of the Big Desert. Photo: William Geary

Throughout our expedition we managed to happen across a range of reptiles (Mallee Dragons, a Burton’s Legless Lizard & Stumpy Tailed Lizards) as well as the standard mobs of Emus and Western Grey Kangaroos. However, perhaps the most fun aspect was deciphering the origin of the plethora of animal tracks found in the sandy soil. Everything from echidna and dingo to legless lizard and emu tracks were spotted. Following one particular track in the sand resulted in a particularly excellent encounter with a Burton’s Legless Lizard. A definite trip highlight.

Given the recent cold snap, the reptiles will be well and truly hidden away when the time comes for the next Big Desert Adventure. Despite this, I’ll hopefully have some exciting camera trap pictures to share, as well as more photos of the beautiful landscape that is Victoria’s mallee.