But we’ve found one mammal in particular that can outsmart cats and live alongside them: the long-nosed potoroo.
These miniature kangaroo-like marsupials are officially listed as vulnerable. And after the recent devastating fires, extensive swathes of their habitat in southeastern Australia were severely burnt, leaving them more exposed to predators such as foxes and cats. But the true extent of the impact on their numbers remains unclear.
Amid the devastation, our new study is reason to be optimistic.
Using motion-sensing camera traps on the wildlife haven of French Island – which is free of foxes, but not cats – we found potoroos may have developed strategies to avoid prowling cats, such as hiding in dense vegetation.
If these long-nosed potoroos can co-exist with one of the world’s most deadly predators, then it’s time we rethink our conservation strategies.
We conservatively estimated that between five and 14 cats lived in our study area (but it takes only one cat to eradicate a population of native animals).
Although cats were common here, we detected them less often in areas of dense vegetation. By contrast, this was where we found potoroos more often.
Long-nosed potoroos are nocturnal foragers that mainly, but not exclusively, feed in more open habitat before sheltering in dense vegetation during the day. But we found potoroos rarely ventured out of their thick vegetation shelter.
This may be because they’re trading off potentially higher quality foraging habitat in more open areas against higher predation risk. In other words, it appears they’ve effectively learnt to hide from the cats.
Another intriguing result from our study was that although potoroos and feral cats shared more than half of their activity time, the times of peak activity for each species differed.
Cats were active earlier in the night, while potoroo activity peaked three to four hours later. This might be another potoroo strategy to avoid becoming a cat’s evening meal.
Still, completely avoiding cats isn’t possible. Our study site was in the national park on French Island, and it’s likely cats saturate this remnant patch of long-nosed potoroo habitat.
It’s also possible cats may be actively searching for potoroos as prey, and indeed some of our camera images showed cats carrying young long-nosed potoroos in their mouths. These potoroos were more likely killed by these cats, rather than scavenged.
Cats are exceedingly difficult to manage effectively. They’re adaptable, elusive and have a preference for live prey.
The two most common management practices for feral cats are lethal control and exclusion fencing. Lethal control needs to be intensive and conducted over large areas to benefit threatened species.
And outside of predator-free sanctuaries, it must be ongoing. If control stops, cats can reinvade from surrounding areas.
“Safe havens” – created through the use of exclusion fencing or predator-free islands – can overcome some of these challenges. But while exclusion fencing is highly effective, it can create other bad outcomes, including an over-abundance of herbivores, leading to excessive grazing of vegetation.
In any case, removing introduced predators might not be really necessary in places native species can co-exist. If long-nosed potoroos have learnt to live with feral cats, we should instead focus on how to maintain their survival strategies.
It’s clear cats are here to stay, so we shouldn’t simply fall back largely on predator eradication or predator-free havens as the only way to ensure our wildlife have a fighting chance at long-term survival.
Yes, for some species, it’s vital to keep feral predators away. But for others like long-nosed potoroos, conserving and creating suitable habitat and different vegetation densities may be the best way to keep them alive.
But perhaps most important is having predator-savvy insurance populations, such as long-nosed potoroos on French Island. This is incredibly valuable for one day moving them to other areas where predators – native or feral – are present, such as nearby Phillip Island.
In the absence of predators, native wildlife can rapidly lose their ability to recognise predator danger. Programs aimed at eradicating introduced predators where they’re co-existing with native species need to pay careful attention to this.
Euan Ritchie, Associate Professor in Wildlife Ecology and Conservation, Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University; Amy Coetsee, Threatened Species Biologist, University of Melbourne; Anthony Rendall, Associate Lecturer in Conservation Biology, Deakin University; Tim Doherty, ARC DECRA Fellow, University of Sydney, and Vivianna Miritis, PhD Candidate, University of Sydney
Jaana Dielenberg, The University of Queensland; Brett Murphy, Charles Darwin University; Chris Dickman, University of Sydney; John Woinarski, Charles Darwin University; Leigh-Ann Woolley, Charles Darwin University; Mike Calver, Murdoch University, and Sarah Legge, Australian National University
We know feral cats are an enormous problem for wildlife – across Australia, feral cats collectively kill more than three billion animals per year.
But pet cats are wreaking havoc too. Our new analysis compiles the results of 66 different studies on pet cats to gauge the impact of Australia’s pet cat population on the country’s wildlife.
The results are staggering. On average, each roaming pet cat kills 186 reptiles, birds and mammals per year, most of them native to Australia. Collectively, that’s 4,440 to 8,100 animals per square kilometre per year for the area inhabited by pet cats.
If you own a cat and want to protect wildlife, you should keep it inside. In Australia, 1.1 million pet cats are contained 24 hours a day by responsible pet owners. The remaining 2.7 million pet cats – 71% of all pet cats – are able to roam and hunt.
What’s more, your pet cat could be getting out without you knowing. A radio tracking study in Adelaide found that of the 177 cats whom owners believed were inside at night, 69 cats (39%) were sneaking out for nocturnal adventures.
Just over one-quarter of Australian households (27%) have pet cats, and about half of cat-owning households have two or more cats.
Many owners believe their animals don’t hunt because they never come across evidence of killed animals.
But studies that used cat video tracking collars or scat analysis (checking what’s in the cat’s poo) have established many pet cats kill animals without bringing them home. On average, pet cats bring home only 15% of their prey.
Collectively, roaming pet cats kill 390 million animals per year in Australia.
This huge number may lead some pet owners to think the contribution of their own cat wouldn’t make much difference. However, we found even single pet cats have driven declines and complete losses of populations of some native animal species in their area.
On average, an individual feral cat in the bush kills 748 reptiles, birds and mammals a year – four times the toll of a hunting pet cat. But feral cats and pet cats roam over very different areas.
Pet cats are confined to cities and towns, where you’ll find 40 to 70 roaming cats per square kilometre. In the bush there’s only one feral cat for every three to four square kilometres.
So while each pet cat kills fewer animals than a feral cat, their high urban density means the toll is still very high. Per square kilometre per year, pet cats kill 30-50 times more animals than feral cats in the bush.
Most of us want to see native wildlife around towns and cities. But such a vision is being compromised by this extraordinary level of predation, especially as the human population grows and our cities expand.
Many native animals don’t have high reproductive rates so they cannot survive this level of predation. The stakes are especially high for threatened wildlife in urban areas.
Pet cats living near areas with nature also hunt more, reducing the value of places that should be safe havens for wildlife.
The 186 animals each pet cat kills per year on average is made up of 110 native animals (40 reptiles, 38 birds and 32 mammals).
For example, the critically endangered western ringtail possum is found in suburban areas of Mandurah, Bunbury, Busselton and Albany. The possum did not move into these areas – rather, we moved into their habitat.
Keeping your cat securely contained 24 hours a day is the only way to prevent it from killing wildlife.
It’s a myth that a good diet or feeding a cat more meat will prevent hunting: even cats that aren’t hungry will hunt.
Various devices, such as bells on collars, are commercially marketed with the promise of preventing hunting. While some of these items may reduce the rate of successful kills, they don’t prevent hunting altogether.
And they don’t prevent cats from disturbing wildlife. When cats prowl and hunt in an area, wildlife have to spend more time hiding or escaping. This reduces the time spent feeding themselves or their young, or resting.
In Mandurah, WA, the disturbance and hunting of just one pet cat and one stray cat caused the total breeding failure of a colony of more than 100 pairs of fairy terns.
Keeping cats indoors protects pet cats from injury, avoids nuisance behaviour and prevents unwanted breeding.
Cats allowed outside often get into fights with other cats, even when they’re not the fighting type (they can be attacked by other cats when running away).
Roaming cats are also very prone to getting hit by a vehicle. According to the Humane Society of the United States, indoor cats live up to four times longer than those allowed to roam freely.
Indoor cats have lower rates of cat-borne diseases, some of which can infect humans. For example, in humans the cat-borne disease toxoplasmosis can cause illness, miscarriages and birth defects.
But Australia is in a very good position to make change. Compared to many other countries, the Australian public are more aware of how cats threaten native wildlife and more supportive of actions to reduce those impacts.
It won’t be easy. But since more than one million pet cats are already being contained, reducing the impacts from pet cats is clearly possible if we take responsibility for them.
Jaana Dielenberg, Science Communication Manager, The University of Queensland; Brett Murphy, Associate Professor / ARC Future Fellow, Charles Darwin University; Chris Dickman, Professor in Terrestrial Ecology, University of Sydney; John Woinarski, Professor (conservation biology), Charles Darwin University; Leigh-Ann Woolley, Adjunct Research Associate, Charles Darwin University; Mike Calver, Associate Professor in Biological Sciences, Murdoch University, and Sarah Legge, Professor, Australian National University
Today, the federal court ruled feral horses can be removed from the Victorian high country.
The case was brought by the Australian Brumby Alliance against the Victorian Government in 2018. Since then, the strategic management plan for feral horses has been shelved, allowing feral horse numbers to increase without control.
In the northern area of Kosciuszko National Park numbers jumped from an estimated 3,255 in 2014 to 15,687 in 2019, in the absence of any management.
Expanding numbers of feral horses roaming the Australian Alps – which are listed as a national heritage site – threaten the alp’s ecosystems, soils and unique species. More feral horses is also an animal welfare issue, as horses face starvation during droughts and have been hit by cars in Kosciuszko.
The ruling is a victory for national parks, which can once again be managed to protect native Australian ecosystems and species. But it stands in stark contrast to the NSW government’s controversial legal protection of feral horses.
The Victorian Government’s strategic action plan, released in 2017, was to remove all horses from the Bogong High Plains, where around 100 horses caused cumulative damage to sensitive alpine ecosystems.
The plan also aimed to trap horses in the eastern Victorian alps, but at a rate so low it was unlikely to make a dent in horse numbers.
Not satisfied with retaining thousands of horses in the eastern alps, in 2018, the Australian Brumby Alliance took out a court injunction to stop horse removal from the Bogong High Plains and prevent substantial reduction in horse numbers in the eastern alps.
Twenty-five thousand feral horses in Australia’s alpine parks have damaged peat wetlands listed as threatened under federal and state legislation. Recovery will take decades to centuries.
If the court had ruled in favour of the Australian Brumby Alliance’s case, it would have locked in escalating threats to the environment, including threatening already endangered species such as the alpine she-oak skink.
It would also have given at least informal legitimacy to NSW legislation that protects feral horses in Kosciuszko National Park.
And possibly most damaging, it could have emboldened claims by brumby groups that feral horses should take priority over conservation in other contentious horse hotspots, such as Barmah, Oxley Wild Rivers, Blue Mountains, Guy Fawkes and Barrington Tops National Parks.
The Australian Brumby Alliance argued removing horses from the alps would compromise its heritage value. They claimed feral horses are part of that heritage, including part of the mountain vistas, the pioneering heritage and myths and legends such as the Man from Snowy River.
The counterpoint from Parks Victoria was that it’s possible to remove horses from the alps while protecting the area’s cultural heritage.
It would be like taking cattle out of the high country, but nevertheless recognising pioneering exploits by preserving cattlemen’s huts.
So what did Judge O’Bryan make of this? In a nutshell, the Australian Brumby Alliance did not have a legal hoof to stand on.
He rejected the Australian Brumby Alliance’s argument the Bogong High Plains horse population was likely to be genetically different from other feral horse populations in a way relevant to the case, and rejected claims feral horses could be beneficial to alpine ecosystems.
Judge O’Bryan also rejected the contention that the brumbies are part of the National Heritage values of the Australian Alps and accepted the evidence that feral horses cause substantial environmental damage.
The ruling acknowledged Parks Victoria’s strategic plan to control feral horses was consistent with legal obligations under the Convention on Biological Diversity, the federal EPBC (Environment Protection and Biodiversity Conservation) Act and the state’s Flora and Fauna Guarantee Act.
Laws and the management of protected areas that reduce their integrity are a global concern. A 2017 study found one-third of Australia’s protected areas had been downgraded, reduced in size or had protection removed to make way for tourism ventures and other developments, like Snowy 2.0 in Kosciuszko National Park.
Kosciusko has faced the brunt of recent downgrading, notably where the NSW government voted to legally protect feral horses in 2018.
The Australian Brumby Alliance’s court case threatened similar downgrading for Victoria’s alpine parks. However, state, federal and international laws, that place obligations on Australian governments to conserve native species and ecosystems in protected areas, have helped restore sensible park management.
Toyay’s federal court ruling upholds the right of state agencies to carry out their legal obligations. And it meets the general expectations of Australian society that our national parks exist to conserve native Australian ecosystems and species, particularly as extinction rates in Australia continue at unprecedented rates.
It also reflects the intent of nature conservation laws. National parks are for conserving our natural heritage, the product of millions of years of evolution on this continent.
Brumby advocates concerned about recent European heritage in Australia can protect horses outside of national parks, an approach pioneered successfully in South Australia.
Lily van Eeden, University of Sydney; Chris Dickman, University of Sydney; Jeremy T. Bruskotter, The Ohio State University; Mathew Crowther, University of Sydney, and Thomas Newsome, University of Sydney
Almost one in five Australians think introduced horses and foxes are native to Australia, and others don’t want “cute” or “charismatic” animals culled, even when they damage the environment. So what are the implications of these attitudes as we help nature recover from bushfires?
Public opposition to culling programs is often at odds with scientists and conservationists.
These tensions came to the fore last month when scientists renewed calls for a horse-culling program to protect native species in Kosciusko National Park – a move strongly opposed by some members of the public.
To manage the environment effectively, including after bushfires, we need to understand the diversity of opinion on what constitutes a native animal, and recognise how these attitudes can change.
In Australia, native species are usually defined as those present before European settlement in 1788. Lethal pest control usually targets species introduced after this time, such as horses, foxes, deer, rabbits, pigs, and cats.
But fire makes native fauna more vulnerable to introduced predators. Fire removes ground layer vegetation that small wildlife would use as protective cover. When this cover is gone, these animals are easier targets for predators like cats and foxes.
State governments have started to respond to this impending crisis. In January, the New South Wales government announced its largest ever program to control feral predators, in an effort to protect native fauna after the fires.
The plan includes 1500-2000 hours of aerial and ground shooting of deer, pigs, and goats and distributing up to a million poison baits targeting foxes, cats, and dingoes over 12 months.
Similarly, the Victorian government announced a A$17.5 million program to protect biodiversity the fires affected, including A$7 million for intensified management of threats like introduced animals.
But will the public be on board? Widespread media coverage of the recent fires and their impacts on wildlife, including the loss of more than a billion animals, might garner support for protecting native wildlife from pests.
On the other hand, efforts to manage animals such as cats and horses might be hampered by a lack of public support for culling charismatic animals that many people value or view as belonging in Australia now.
The distinctions many Australians draw – native animals are “good” and introduced species are “bad” – shape how people view conservation efforts. A survey we conducted in 2017 found people more likely to disapprove of lethal methods for managing species they perceived to be native.
In the same survey, we found nearly one in five Australians considered horses and foxes to be native to Australia.
This suggests either that a) people lack knowledge of Australia’s natural history or b) people disagree with conservationists’ definition of animal “nativeness”.
Many introduced species, such as horses and foxes, have existed in Australia for more than a century and have established populations across much of the country. It’s unlikely they’ll ever be eradicated.
Some people, including scientists, say we should just accept introduced species as part of Australia’s fauna. They argue current management justifies killing based on moral, not scientific judgements and introduced animals may increase biodiversity.
But the issue remains extremely divisive. A central tenet of traditional conservation is that humans have a duty to protect native species and ecosystems from the threat introduced species pose. It’s difficult to do this without culling introduced animals.
Animal welfare concerns may also drive opposition to culling, taking the view that all animals, even non-natives, have intrinsic value and the right to live.
What’s more, non-native culling programs can be controversial when the animal is considered “cute” or “charismatic”, or of cultural value. For example, a plan to cull feral horses in the Kosciusko National Park in 2018 was met with public outrage, prompting the NSW government to overturn the decision.
Yet protecting introduced species in national parks goes against the very reason they were created – to conserve native ecosystems and species.
When analysing public attitudes towards various species, we must also consider how attitudes shift over time.
In Australia, non-native animals such as domestic camels and donkeys were considered useful for transport and highly valued. But we ultimately turned them loose and relabelled them as pests when we started using cars.
Interestingly, we’ve already accepted some introduced species as native. Humans brought dingoes to Australia at least 3,500 years ago. They’re described as native under Australian biodiversity legislation, and 85% of our 2017 survey participants considered dingoes to be native.
Perhaps its only a matter of time until more recently arrived species like horses and foxes are counted as native. Some scientists argue this shift should be based on how ecosystems and species adapt to these new arrivals. For example, some small Australian mammals show fear of dingoes or dogs, but they haven’t yet learnt to fear cats.
Native species, such as kangaroos and possums, may also be culled if they’re perceived to be overabundant or damaging economic interests like agriculture.
While the plight of bushfire-affected koalas on Kangaroo Island attracted considerable media interest, and the immediate welfare of any animal affected by fires is always a concern, koalas were actually introduced there.
They’ve been managed as a pest on Kangaroo Island for more than 20 years, and it’s unlikely the rescued koalas will be returned to the island. In this case, public concern transcends the distinction between native and introduced.
We might never all agree on how best to manage native and non-native species. But effective environmental management, including after bushfires, requires understanding the diversity of opinion.
Doing so can help to develop management plans the public supports and allow effective communication about management that is controversial.
In fact, the NSW Office of Environment and Heritage did undertake an extensive public consultation process in developing their horse management plan for Kosciuszko National Park, but it wasn’t used after the “brumby bill” gave horses protection in 2018.
With human lives and many animal lives lost, response to the bushfires is already highly emotive. Failure to consider public attitudes towards managing animals will lead to backlash, wasted money and time, and continuing decline of the native species whose conservation is the goal of these actions.
Lily van Eeden, PhD Candidate in Human-Wildlife Conflict, University of Sydney; Chris Dickman, Professor in Terrestrial Ecology, University of Sydney; Jeremy T. Bruskotter, Professor, School of Environment and Natural Resources, The Ohio State University; Mathew Crowther, Associate professor, University of Sydney, and Thomas Newsome, Lecturer, University of Sydney
On Friday I flew in a helicopter over the fire-ravaged Kosciuszko National Park. I was devastated by what I saw. Cherished wildlife species are at grave risk of extinction: those populations the bushfires haven’t already wiped out are threatened by thousands of feral horses trampling the land.
The New South Wales park occupies the highest mountain range in Australia and is home to plants and animals found nowhere else in the world. Many of these species are threatened, and their survival depends on protecting habitat as best we can.
Kosciuszko National Park provides habitat for two species of corroboree frog (critically endangered), the alpine she-oak skink (endangered), broad-toothed rat (vulnerable) and stocky galaxias (a critically endangered native fish), among other threatened species.
As the climate has warmed, the cool mountain habitat of these species is shrinking; bushfires have decimated a lot of what was left. Feral horses now threaten to destroy the remainder, and an urgent culling program is needed.
Australia’s plants and ecosystems did not evolve to withstand trampling by hard-hooved animals, or their intensive grazing. Unfortunately, the New South Wales government has allowed the population of feral horses in the park to grow exponentially in recent years to around 20,000.
I flew over the northern part of the park with members of the Invasive Species Council, who were conducting an urgent inspection of the damage. Thousands of hectares were completely incinerated by bushfires: not a green leaf was visible over vast areas. A cataclysm has befallen the western face of the mountains and tablelands around Kiandra and Mount Selwyn.
Further north and east of Kiandra the fires were less intense and burnt patchily. On Nungar Plain the grassland and peat wetlands were only lightly burnt, and the first green shoots were already visible along the wetlands of the valley floor.
At first, I wondered if the fires may have spared two animals which live in tunnels in the vegetation on the sub-alpine high plains: the alpine she-oak skink and broad-toothed rat (which, despite the name is a cute, hamster-like creature).
But not only was their understory habitat burnt, a dozen feral horses were trampling the peat wetlands and eating the first regrowth.
On the unburnt or partially burnt plains a few ridges over, 100 or more horses were mowing down the surviving vegetation.
Next we flew over a small stream that holds the last remaining population of a native fish species, the stocky galaxias. A small waterfall is all that divides the species from the stream below, and the jaws of the exotic trout which live there.
The aftermath of the fires means the last refuge of the stocky galaxias is likely to become even more degraded.
Over the years, feral horses have carved terraces of trails into the land causing erosion and muddying the stream bank. As more horses congregate on unburnt patches of vegetation after the fires, more eroded sediment will settle on the stream bed and fill the spaces between rocks where the fish shelter. Ash runoff entering the stream may clog the gills of the fish, potentially suffocating them.
Many key wetland habitats of the southern and northern corroboree frogs have also been burnt. These striking yellow and black frogs nest in wetland vegetation.
We hovered over a key wetland for the northern corroboree frog that had not been burnt, deep in the alpine forest. A group of feral horses stood in it. They had created muddy wallows, trampled vegetation and worn tracks that will drain the wetland if their numbers are not immediately controlled.
We saw no dead horses from the air. Unlike our native wildlife, most appear to have escaped the fires.
Flying down the upper Murrumbidgee River’s Long Plain, I saw large numbers of feral horses gathered in yet more wetlands. Displaced by the fires to the south and west, they were already trampling the mossy and heathy wetlands that store and filter water in the headwaters.
The Murrumbidgee River is a key water source for south-east Australia. The horses stir up sediment and defecate in the water. They create channels which drain and dry the wetlands, exposing them to fire.
One-third of Kosciuszko National Park has been burnt out and at the time of writing the fires remain active. Feral horses are badly compounding the damage.
If we don’t immediately reduce feral horse numbers, the consequences for Kosciuszko National Park and its unique Australian flora and fauna will be horrendous.
Responsible managers limit the numbers of livestock on their lands and control feral animals. The NSW government must repeal its 2018 legislation protecting feral horses in Kosciuszko National Park, and undertake a responsible control program similar to those of the Australian Capital Territory and Victorian governments.
Without an emergency cull of feral horses in Kosciuszko National Park, burnt vegetation may not fully recover and threatened species will march further towards extinction.
Feral horse numbers have more than doubled in the past five years in the Australian Alps, according to results just released from the Australian Alps Feral Horse Aerial Survey. In one of the three survey blocks, North Kosciuszko, feral horse numbers have risen from an estimated 3,255 in 2014 to 15,687 in 2019, a near five-fold increase.
Scientists warned the government that very high numbers of horses would be the inevitable consequence of its inaction over horse management.
More than just allowing numbers to increase, the NSW parliament legislated to protect feral horses within Kosciuszko National Park, effectively prioritising the preservation of horse populations over native alpine species and environmental values, where they are in conflict.
This was despite the strong advice from scientists, and amid substantial controversy around the origins and timing of the bill.
High feral horse numbers forced the closure of the popular Blue Waterholes campground in November, after substantial risks and several injuries to visitors were reported. Freedom of information requests were needed to bring to light crashes between cars and feral horses in Kosciuszko.
Despite the NSW government trying to keep this information from reaching the public, several incidents of feral horses being struck by vehicles have now been reported.
The community group Reclaim Kosci has warned it is only a matter of time before someone is killed in a collision with a feral horse unless numbers are drastically and rapidly reduced.
Besides impacts on people, the lack of effective feral horse policy in NSW has now set the stage for another mass animal welfare disaster.
With an estimated 25,318 feral horses distributed across the surveyed area (more than 7,400 square kilometres) of the Australian Alps, many thousands of horses will face starvation when the region next burns. This is predictable, inevitable and tragically also completely avoidable had effective feral horse control been implemented.
The prolonged drought hitting Australia has worsened the impacts of horses in the high country. Plants already struggling to survive are being trampled and grazed, and areas around standing water resemble feedlots.
These impacts will worsen over summer, both for the national park and the horses themselves, with herds suffering in the heat and struggling to survive. Horses starved to death along the snowy river in Kosciuszko in 2018.
Now many more animals are at risk of this fate because scientifically-supported solutions have been dismissed by NSW deputy premier John Barilaro.
Evidence presented at the Kosciuszko Science Conference and research published earlier this year showed how a broad range of Alpine species and ecosystems were being affected by feral horses. These effects will now be more intense and occur across more of Australia’s ecologically sensitive and biodiverse alpine environments.
For example, the native broad toothed rat depends on dense vegetation along watercourses. With feral horses eating out or trampling plants along streams, these delightful, rotund fur-balls may lose their homes, and hence be more exposed to the elements and predators.
Right now, feral horses are reducing the habitat for these animals, causing already threatened populations to become smaller and more fragmented. As these small populations blink into extinction we can expect widespread losses across the national park.
Corroboree frogs will now be under enormous pressure. We already know feral horses destroy the wetlands these iconic yellow-striped black frogs depend on for breeding. This destruction will likely now impact many more swamps, reducing breeding success and reducing options for reintroduction of this critically endangered frog.
Another species, the Stocky Galaxias, teeters on the brink of extinction. This small native fish now only lives in a 3km stretch of stream in Kosciuszko National Park. Feral horses trample the river banks and rip out vegetation that causes silt to accumulate in the stream.
This is disastrous for the fish, which breed beneath boulders in the stream. If silt fills up the gaps beneath boulders, there is no place for the fish to lay eggs.
The high numbers of feral horses in Kosciuszko mean this process of stream destruction will likely worsen, potentially hastening the demise of this species unique to Kosciuszko National Park.
Hope for change now rests with the new feral horse management plan being developed by the recently established Kosciuszko National Park Wild Horse Community Advisory Panel and the Wild Horse Scientific Advisory Panel. The community panel has expressed interest in working with the scientific panel, and such collaboration will be essential for making progress.
These committees will need to consider all options for resolving this human safety, animal welfare, and ecological crisis. Although trapping is crueller and many times more expensive than aerial culling, if the trapping effort is substantially ramped up across the park, it could potentially limit population growth and reduce horse numbers.
Aerial culling, despite being the most cost-effective and humane method to lower the horse population size and reduce impacts, is misrepresented by the pro-brumby lobby and sections of the media as cruel, and hence has been deemed unacceptable. These costs, and animal welfare and political trade-offs, must be carefully considered by the committees.
The scientific committee said the draft plan for action will be open for comment in February 2020 to meet NSW environment minister Matt Kean’s deadline for a final plan by May 1, 2020. This rapid timeframe is absolutely essential, as the increase of feral horses in the Alpine National Park will not abate any time soon without urgent and substantial control measures.
Don Driscoll, Professor in Terrestrial Ecology, Deakin University; David M Watson, Professor in Ecology, Charles Sturt University, and Euan Ritchie, Associate Professor in Wildlife Ecology and Conservation, Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University
Arian Wallach, University of Technology Sydney; Chelsea Batavia, Oregon State University; Danielle Celermajer, University of Sydney; Daniel Ramp, University of Technology Sydney; Erick Lundgren, University of Technology Sydney, and Esty Yanco, University of Technology Sydney
As the world struggles to keep tabs on biodiversity decline, conservation largely relies on a single international database to track life on Earth. It is a mammoth and impressive undertaking – but a glaring omission from the list may be frustrating conservation efforts.
In defence of invasive alien species
The International Union for the Conservation of Nature’s Red List aims to be a “complete barometer of life”. But non-native wildlife is excluded from the list.
Our study, published today in the journal Conservation Biology, questions the wisdom of this omission. It means, for example, vulnerable species facing existential threats in their “home country” may be exterminated freely in another. Excluding these animals, such as wild camels in Australia, and rare Australian frogs living overseas, distorts conservation science.
The concept of “native” draws a sharp line between species that count and those that don’t. It is essentially an ethical choice, and a disputed one at that. Regardless of whether one defends or disputes the concept, it is problematic to use a moral term to filter a critical source of scientific data.
The invisible components of biodiversity – those populations excluded from conservation’s definition of life – can be found in trash lists, where they are described as invasive, aliens, pests, and feral.
So what does the world look like if we include all wildlife in biodiversity assessments? We rummaged around in the “trash piles” to find out.
By focusing on Australian non-native vertebrate species – amphibians, birds, fishes, mammals, and reptiles – we did something many conservationists would find unthinkable. We added unloved species such as feral cats, cane toads, the Indian myna, and carp to Australia’s biodiversity counts.
We created maps showing the range of 87 species whose ancestors were introduced into Australia, and 47 species native to Australia that were introduced elsewhere, since European colonisation.
Many of these so-called invasive species are at risk of extinction in their native ranges; 32% are assessed as threatened or decreasing in the Red List. For 15 of them, non-native ranges provide a lifeline.
Not only does Australia contribute to the survival and flourishing of these species, but immigrant vertebrates have also added 52 species to the number of vertebrate species in Australia (after accounting for extinctions).
This number in no way indicates that non-native species replace or make up for those that have been lost. And it does not exonerate humans of their role in causing extinctions. But the current data do not even allow us to acknowledge that these species exist.
Because they are not counted in conservation, these non-native populations are subjected to mass eradication programs. Paradoxically, in assessing how such programs are justified, we found conservation is the most frequently cited reason for killing these wild animals.
Dromedary camels were extinct in the wild for some 5,000 years until they “went feral” in Australia, where they are now endemic. Rather than celebrating what is arguably the most extraordinary rewilding event in the world, wild camels were declared a pest. Between 2009 and 2013, Australia spent A$19 million to gun down 160,000 individuals of a species found nowhere else on Earth in the wild.
Likewise, 89% of the global distribution of Javan rusa, a deer species vulnerable to extinction, is in Australia. As pest, they are culled and hunted for sport.
Nativism not only renders countless species invisible, along with their unique and fascinating ecologies; it also exposes them to unfettered, unscientific, unmonitored, and unlamented mass killing programs.
Mass killing of non-native species, if questioned at all, is generally explained as protecting native species. But ecology is complex. One cannot simply assume that all non-native populations, in all contexts, do nothing but harm.
Where non-native species do contribute to the loss of native species, humans need to confront the ethical complexities and shoulder real responsibility, rather than simply reach for a gun as a first solution.
In many situations changing harmful human behaviours, like persecuting apex predators such as dingoes, can solve problems that appear to be caused solely by non-native species.
Irrespective of whether we value non-native species or not, there is no scientific justification for expunging large swaths of the living world from conservation data. Smuggling ethically dubious distinctions into data harms conservation science, and has grave repercussions.
The toad we love to hate
Persisting with the assumption that we have the right to pick and choose which species “count” looks like playing God. By now, we should have learned we must not.
Arian Wallach, Lecturer, Centre for Compassionate Conservation, University of Technology Sydney; Chelsea Batavia, Postdoctoral research associate, Oregon State University; Danielle Celermajer, Professor of Sociology and Social Policy, University of Sydney; Daniel Ramp, Associate Professor and Director, Centre for Compassionate Conservation, University of Technology Sydney; Erick Lundgren, PhD Student, Centre for Compassionate Conservation, University of Technology Sydney, and Esty Yanco, PhD Candidate, Centre for Compassionate Conservation, University of Technology Sydney
There is a widespread belief dingoes are as good as extinct in New South Wales and nearly all dog-like animals in the wild are simply wild dogs. This belief is bolstered by legislation and policies in NSW, which have removed the word dingo and refer only to “wild dogs”.
But our research, recently published in the journal Conservation Genetics, challenges this assumption. We performed DNA ancestry testing, much like the ancestry tests available to people, on 783 wild canines killed as part of pest control measures in NSW.
Roughly one in four of the animals we tested were pure dingoes, and most were genetically more than three-quarters dingo. Only 5 of the 783 animals we tested turned out to be feral domestic dogs with no dingo ancestry.
This policy requires all public and private landholders in NSW to display signs warning when poison baits have been laid to kill wild dogs.
But our DNA testing found three hotspots of high dingo ancestry within northeastern NSW: Washpool National Park; the coast north of Port Macquarie; and the Myall lakes region.
There were more pure dingoes in these areas. Despite these positive findings, dingo-dog hybridisation is still very prevalent in NSW. Three-quarters of wild animals carry some domestic dog ancestry.
This is not entirely surprising. Domestic pet and working dogs have lived alongside dingoes for centuries. Widespread killing of dingoes also increases the risk of hybridisation because it breaks family groups apart, giving domestic dogs the opportunity to mate with dingoes. Small populations also have a higher risk of hybridisation.
Hybridisation is generally considered detrimental to conservation because it alters the genome. In the case of dingoes, hybridisation is a problem because hybrids may be different to dingoes and “true” dingoes will eventually disappear.
While our results show dingoes still exist and their genes are predominate, their conservation will be greatly helped if we can prevent further interbreeding with domestic dogs.
Our study has important implications for both how we describe dingoes, and the future conservation of dingoes in NSW. Most of the animals labelled as wild dogs in NSW had predominantly dingo DNA, and fewer than 1% were actually feral dogs.
The term wild dog obfuscates the identity of wild animals whose genes are mostly dingo but sometimes carry dog genes. For all intents and purposes, these animals have dingo DNA, look like dingoes and behave like dingoes, and consequently should be labelled as dingoes rather than escaped pets gone wild.
Hotspots with high dingo ancestry have significant conservation value and urgently need new management plans to ensure these pure dingo populations are protected from hybridisation. These populations could be protected by restricting the killing of dingoes in these areas and restricting access to domestic dogs on public land such as state forests.
Further ancestry testing should be conducted in more areas to determine whether there are other pockets of high dingo purity in NSW.
Undeniably, dingoes can negatively impact livestock producers, especially sheep farmers. Non-lethal strategies such as electric or exclusion fencing, and livestock guarding animals such as dogs, llamas and donkeys, may balance the need to conserve dingoes and protect vulnerable livestock.
In some circumstances, dingoes can benefit farmers because they reduce numbers of native and feral herbivores like kangaroos, feral goats, rabbits and pigs, boosting pasture growth for livestock.
If lethal control is justified, then targeted strategies such as shooting and trapping may be more suitable in high dingo conservation areas rather than landscape-wide poison aerial baiting.
It is time to resurrect the dingo. The term dingo needs to come back into official language, and we need practical strategies for limiting dingo-dog hybridisation and protecting dingo hotspots.
Kylie M Cairns, Research fellow, UNSW; Brad Nesbitt, Adjunct Research Fellow, University of New England; Mathew Crowther, Associate professor, University of Sydney; Mike Letnic, Professor, Centre for Ecosystem Science, UNSW, and Shawn Laffan, Associate professor, UNSW
Australia’s water rats, or Rakali, are one of Australia’s beautiful but lesser-known native rodents. And these intelligent, semi-aquatic rats have revealed another talent: they are one of the only Australian mammals to safely eat toxic cane toads.
Our research, published today in Australian Mammalogy, found water rats in Western Australia adapted to hunt the highly poisonous toads less than two years after the toads moved into the rats’ territory.
The rats, which can grow to over 1kg, are the only mammal found to specifically target large toads, neatly dissecting the toads to eat their hearts and livers while avoiding the poisonous skin and glands.
Water rats are nocturnal and specially adapted to live in waterways, with webbed feet and soft water-resistant fur. Their fur is so impressive there was once a thriving water rat fur industry in Australia.
They can be found in lakes, rivers and estuaries, often living alongside people, in New South Wales, Queensland, Tasmania, South Australia, far north and southwest Western Australia, the Northern Territory, and Victoria, where they can even be seen along St Kilda Pier.
Water rats are also highly intelligent, as shown by their rapid adaptation to hunting and eating one of Australia’s most toxic introduced species – the invasive cane toad.
Cane toads were introduced to Australia in 1935 in an ill-fated attempt to control the cane beetle. They have spread across the north of the country at up to 60km per year, leaving devastation in their wake. Many native species, such as northern quolls, yellow-spotted monitors, and crocodiles, have suffered widespread declines, and in some cases local extinctions, as a result of eating cane toads.
The toads secrete a toxin in their parotoid glands (on the back, neck and shoulders) that can be fatal even in very small doses.
Cane toads arrived at our field site in the Kimberley, Western Australia, in 2011-12, leading to a crash in the populations of predators including numerous lizards and northern quolls.
However, in 2014 we found a creek dotted with the bodies of cane toads that had clearly been attacked. Every morning we discovered up to five new dead toads with small, near-identical incisions down their chest in just a five-metre stretch of creek. What was using almost surgical precision to attack these toads?
Post-mortem analysis showed that in larger toads the heart and liver had been removed, and the gall bladder (which contains toxic bile salts) neatly moved outside the chest cavity. In medium-sized toads, besides the removal of the heart and liver, one or both back legs had been stripped of their toxic skin and the muscle also eaten.
The finding intrigued us enough to dissect waterlogged and rotting toad bodies in 40℃ heat. Using remote infrared camera footage and analysis of the bites left on the muscle, we found our clever attacker – the native water rat!
While there have been anecdotal reports of water rats eating toads in Queensland and the Northern Territory, there were no published reports of this in Western Australia, where the toad was a more recent arrival.
We also didn’t know whether rats could tolerate the toad toxins, or were targeting non-toxic parts of the body. And we wanted to find out whether the rats were targeting small (and less toxic) toads, as some other rodent species do, or were deliberately going after larger toads which are a better source of food.
During our study we captured and measured more than 1,800 cane toads in just 15 days in the vicinity of the water rats’ creek. The vast majority, 94%, were medium-sized; 3.5% were small (less than 4cm long); and just 2.5% were large (greater than 10cm long).
But despite medium toads being far more common, three quarters of the dead toads we found were large, and the remainder were medium. No small toad bodies were found or observed being attacked.
While some species, such as keelback snakes and several birds (including black and whistling kites, and crows) can eat cane toads, there has been less evidence of mammals hunting this new type of prey and living to tell the tale.
Some rodents can eat small juvenile toads, but no rodents have been documented specifically targeting large toads. In our case, water rats preferred to eat large toads, despite medium-sized toads outnumbering them by 27 to 1.
We’re not sure whether water rats have very rapidly learned how to safely attack and eat cane toads, or if they are adapting a similar long-term hunting strategy that they may use to eat toxic native frogs.
Water rats are very well placed to pass on hunting strategies, as they care for their offspring for at least four weeks after they finish producing milk. This could help spread the knowledge of toad hunting across streams and creeks over time.
While this behaviour seems to be confined to local populations, if these tactics spread, water rats may be able to suppress toad populations when they reach water bodies – another small line of defence against this toxic killer.
Marissa Parrott, Reproductive Biologist, Wildlife Conservation & Science, Zoos Victoria, and Honorary Research Associate, BioSciences, University of Melbourne; Sean Doody, Conjoint Fellow, University of Newcastle, and Simon Clulow, MQ Research Fellow, Macquarie University