Australia must control its killer cat problem. A major new report explains how, but doesn’t go far enough

Sarah Legge, Australian National University; Chris Dickman, University of Sydney; Jaana Dielenberg, Charles Darwin University; John Woinarski, Charles Darwin University, and Tida Nou, The University of Queensland

Australia is teeming with cats. While cats make great pets, and can bring owners emotional, psychological and health benefits, the animals are a scourge on native wildlife.

Cats kill a staggering 1.7 billion native animals each year, and have played a major role in most of Australia’s 34 mammal extinctions. They continue to pose an extinction threat to at least another 120 species.

Long-nosed potoroo — The long-nosed potoroo is extremely vulnerable to cats.
Shutterstock

A recent parliamentary inquiry into the problem of feral and pet cats in Australia has affirmed the issue is indeed of national significance. The final report, released last week, calls for a heightened, more effective, multi-pronged and coordinated policy, management and research response.

As ecologists, we’ve collectively spent more than 50 years researching Australia’s cat dilemma. We welcome most of the report’s recommendations, but in some areas it doesn’t go far enough, missing major opportunities to make a difference.

Night curfews aren’t good enough

The report recommends Australia’s 3.8 million pet cats be subject to night-time curfews. This measure would benefit native nocturnal mammals, but won’t save birds and reptiles, which are primarily active during the day.

Pet cats kill 83 million native reptiles and 80 million native birds in Australia each year. From a wildlife perspective, keeping pet cats contained 24/7 is the only responsible option.

It’s clearly possible: one third of Australian pet cat owners already keep their pets contained all the time.

Stopping pet cats from roaming is also good for the cats, which live longer, safer lives when kept exclusively indoors. It would also substantially reduce the number of people falling ill from cat-dependent diseases each year.

Other strategies for improving pet cat management proposed in the report include pet cat registration, subsidised programs for early age desexing, public education campaigns to promote responsible pet cat ownership, and improving the consistency of rules and legislation nationally.

Cat on a windowsill — Indoor cats live longer than cats allowed to roam.
Jaana Dielenberg

The report is also unambiguously opposed to “trap-neuter-release” programs, in which un-owned cats in urban areas are desexed and then released. We agree with this finding, as these programs aren’t effective at reducing the population of stray cats, nor preventing those cats from killing wildlife and spreading disease.

We need more wildlife havens

One of the inquiry’s flagship recommendations is a national conservation project dubbed “Project Noah”. This would involve an ambitious expansion of Australia’s existing network of reserves free from introduced predators, both on islands and in mainland fenced areas. The reserves provide havens — or a fleet of “arks” — for vulnerable native wildlife.

This measure is vital. 2019 research found Australia has more than 65 native mammal species and subspecies that can’t persist, or struggle to persist, in places with even very low numbers of cats or foxes. This includes the bilby, numbat, quokka, dibbler and black-footed rock wallaby.

Australia already has more than 125 havens, 100 of which are islands. These have prevented 13 mammal species from going extinct, such as boodies and greater stick-nest rats. In total, these havens have protected populations of 40 mammal species susceptible to cats and foxes.

This is a good start, but we need more investment in havens to prevent extinctions. More than 25 species are highly sensitive to cat and fox predation, but aren’t yet protected in the haven network. This includes the central rock-rat, which is more likely than not to become extinct within 20 years without new action.

What’s more, some species, such as the long-nosed potoroo, exist in just one haven. To avoid issues such as inbreeding and to ensure disasters like a fire at any single haven don’t take out an entire species, each species should be represented across several havens, in reasonable population sizes.

The report didn’t specify how the havens network should be expanded. But 2019 research found to get each species needing protection into at least three havens, Australia requires at least 35 new, strategically located islands or mainland fenced areas.

Fence with scenic hills behind — The predator proof fence at the Australian Wildlife Conservancy’s Newhaven Sanctuary, one of the largest cat- and fox-free havens on mainland Australia.
Australian Wildlife Conservancy

What about the rest of the country?

Havens cover less than 1% of Australia. So what we do in the other 99% of the landscape — including across conservation reserves like national parks — is vital.

Yet the parliamentary inquiry report lacks clear recommendations to expand cat control more broadly, including at important conservation sites such as in Kakadu National Park.

The impact of roaming pet cats on Australian wildlife.

The report reaffirms the need to cull feral cats, and to set new targets for culling, without specifying what those targets are. We agree some culling is important, especially at sites with very vulnerable threatened wildlife.

But in many parts of Australia, broad-scale habitat management is a more cost-effective way to reduce cat harm. This involves making habitat less suitable for cats and more suitable for native wildlife, for example, by reducing rabbit numbers, fire frequency and grazing by feral herbivores such as cattle and horses.

Research has shown fewer rabbits leads to fewer cats. Rabbits are a favoured prey of many cats, so they boost feral cat numbers, which then also hunt native wildlife.

And cats gravitate to areas with less vegetation because it’s easier to catch prey. These areas include those with frequent fires, or where feral herbivores have reduced vegetation through grazing and trampling.

Better habitat with more vegetation gives native animals places to hide from predators, and more food and shelter. It’s a bit like giving the last little pig a house of bricks instead of trying to fist-fight the wolf.

Feral horses, such as these in Kakadu National Park, eat and damage vegetation making conditions more favourable for cats to hunt.
Jaana Dielenberg

A major step forward

Over the past two decades, Australia has slowly woken up to the damage cats cause to nature. This has led to more research, management and policy to address the problem.

Some state governments, environment groups and scientists have worked hard to develop feral cat control options, and the 2015 Australian Threatened Species Strategy did much to focus national attention and resourcing to the issue.

The parliamentary inquiry is a major step forward, and many recommendations are sound. But overall, its recommendations call for incremental improvement.

Australia’s laws clearly fail to provide a safety net for wildlife. The cat issue is part of a larger problem with how we manage habitat, biodiversity and threats to nature – and fixing that requires wholesale change.

Sarah Legge, Professor, Australian National University; Chris Dickman, Professor in Terrestrial Ecology, University of Sydney; Jaana Dielenberg, University Fellow, Charles Darwin University; John Woinarski, Professor (conservation biology), Charles Darwin University, and Tida Nou, Project officer, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Cats carry diseases that can be deadly to humans, and it’s costing Australia $6 billion every year

Sarah Legge, Australian National University; Chris Dickman, University of Sydney; Jaana Dielenberg, The University of Queensland; John Read; John Woinarski, Charles Darwin University; Pat Taggart, and Tida Nou, The University of Queensland

Toxoplasmosis, cat roundworm and cat scratch disease are caused by pathogens that depend on cats — pets or feral — for part of their life cycle. But these diseases can be passed to humans, sometimes with severe health consequences.

In our study published today in the journal Wildlife Research, we looked at the rates of these diseases in Australia, their health effects, and the costs to our economy.

Professor Sarah Legge discusses the key findings of the study.

Based on findings from a large number of Australian and international studies, Australian hospital data and information from the Australian Bureau of Statistics, we estimate many thousands of people in Australia fall ill or sustain a minor injury as a result of cat-dependent diseases each year.

Our estimations suggest more than 8,500 Australians are hospitalised and about 550 die annually from causes linked to these diseases.

We calculated the economic cost of these pathogens in Australia at more than A$6 billion per year based on the costs of medical care for affected people, lost income from time off work, and other related expenses.

Toxoplasmosis

Toxoplasmosis is an illness caused by the parasite Toxoplasma gondii. It’s the most serious cat-dependent disease.

Newly infected cats shed millions of T. gondii oocysts (like tiny eggs) in their poo and these can survive many months in the environment.

Humans become infected when they ingest these oocysts, which are in the soil and dust in places where cats have defecated, especially sandpits, vegetable gardens or kitty litter.

Humans can also become infected from eating undercooked meat, if those farm animals have come into contact with cat-shed oocysts.

Up to one-third of people globally are infected with T. gondii, most without knowing it. Australian studies have reported infection rates between 22% and 66%.

Once infected, about 10% of people develop illness; the other 90% have no symptoms.

Based on overall infection rates and Australia’s population size, we estimate there are more than 125,000 new infections in Australia each year.

Of these, around 12,500 people get sick, mostly with non-specific, flu-like symptoms that resolve within a couple of weeks; 650 require hospitalisation, and 50 die, with these more serious cases often experiencing brain swelling and neurological symptoms.

People with compromised immune systems, such as those with cancer or HIV, are at highest risk.

The parasite _Toxoplasma gondii_ — Toxoplasmosis is caused by the parasite *Toxoplasma gondii*.
Yale Rosen/Flickr

Pregnant women who become infected for the first time can miscarry, or their babies may be born with congenital deformities.

Based on reported and estimated T. gondii infection rates in newborns, about 240 infected babies are born in Australia each year.

More than 20%, or about 50 of these babies, will have symptoms that require life-long care, including impaired vision or hearing, and intellectual disabilities. Another 90 babies will develop symptoms, usually related to vision or hearing, later in life.

A woman holds her pregnant belly. — Toxoplasmosis carries unique risks for pregnant women.
Freestocks/Unsplash

Long-term impacts of latent infection

Even if the initial infection causes little illness, the T. gondii parasite stays with us for life, encased in a cyst, often in the brain. These “latent” infections may affect our mental health and behaviour, such as delaying our reaction times.

Many studies have found people with T. gondii infection are more likely to have a car accident. A review of several studies found if there were no T. gondii infections, car accident rates would theoretically be 17% lower.

T. gondii infections also appear more common in people with mental health disorders such as schizophrenia, and in people who attempt suicide. Reviews across many studies suggest that without T. gondii infections, there could be 10% fewer suicides and 21% fewer schizophrenia diagnoses.

There’s still debate over whether the parasite causes car accidents and mental health disorders, or whether the association is explained by another shared factor. But it is possible T. gondii infection is a risk factor for these issues, in the same way smoking is a risk factor for heart attacks.

Scientists are still discovering how T. gondii influences the brain, but studies on rodents suggest it may involve changed brain chemistry or inflammation.

Putting it all together

If we accept T. gondii infections do increase the risk of car accidents, suicides and schizophrenia, then considering the incidence of these accidents and health issues in Australia, without T. gondii, we estimate we could potentially avoid:

200 deaths and 6,500 hospitalisations due to car accidents
300 suicides and 4,500 suicide attempts
800 schizophrenia diagnoses each year.

Combining deaths from car accidents and suicide with the 50 deaths from acute toxoplasmosis, we reach a total of 550 deaths related to T. gondii infection per year.

The hospitalisation total for T. gondii includes 650 for acute toxoplasmosis, 50 for congenitally infected babies, 6,500 for car accidents, and 800 for schizophrenia. We didn’t include hospitalisations for suicide attempts, as we didn’t have statistics on that. So this could be a conservative estimate, notwithstanding the fact there are other factors involved in car accidents and mental health issues.

Cat scratch and roundworm

Cat scratch disease is a bacterial infection (Bartonella henselae) that people can contract if bitten or scratched by an infected cat.

Typical symptoms include sores, fevers, aches and swollen glands. But more serious symptoms, such as inflammation of heart tissue, cysts in the organs and loss of vision, can also occur.

Prevalence figures are not available in Australia, but based on rates in the United States and Europe, where cat ownership patterns and cat infection rates are similar, we estimate at least 2,700 Australians get sick annually from cat scratch disease, and 270 are hospitalised.

Cat roundworm is a parasitic infection (Toxocara cati) that people and other animals can contract by accidentally consuming the parasite’s egg, which infected cats shed in their poo.

Most cat roundworm infections cause mild symptoms, but the migration of the larvae through the body can cause tissue damage, which can be serious if it occurs in a place like the eye or heart.

An adult cat round worm.
Beentree/Wikimedia commons, CC BY

What can we do?

Some 700,000 feral cats and another 2.7 million pet cats roam our towns and suburbs acting as reservoirs of these diseases.

There are no human vaccines for these diseases. Treatment for T. gondii infection in cats isn’t considered useful because cats usually shed the oocysts without the owner even realising the cat has the parasite. Cats can be treated to rid them of roundworm, but treatment for B. henselae (the bacteria that causes cat scratch) may not be effective.

But if you’re a cat owner, there are some things you can do. Keeping pet cats indoors or in a securely contained outdoor area could reduce the chance your pet will contract or pass on a disease-causing pathogen.

A cat sits on the windowsill, looking out onto the street. — If cats are always kept indoors they have a low risk of catching and spreading the disease.
Jaana Dielenberg, Author provided

Cats should be kept out of veggie gardens and children’s sandpits. Washing hands after handling kitty litter and gardening, and washing vegetables thoroughly, can also reduce the risk of transmission.

As T. gondii can be contracted from infected meat, cooking meat well before eating, and not feeding raw meat to pets, can also help.

The urban feral cat resevoir could be reduced by preventing access to food sources such as farm sites, rubbish bins and tips. We could do this with improved waste management and fencing.

People shouldn’t feed feral cats, as this can lead to cat colony formation, where infection rates are also higher.

Pet cats should also be desexed to prevent unwanted litters that end up as free-roaming ferals.

These steps would cost us and our pet cats little, but could prevent unnecessary impacts on our health and well-being.

Sarah Legge, Professor, Australian National University; Chris Dickman, Professor in Terrestrial Ecology, University of Sydney; Jaana Dielenberg, University Fellow, Charles Darwin University. Science Communication Manager, The University of Queensland; John Read, Associate Lecturer, Ecology and Environmental Sciences; John Woinarski, Professor (conservation biology), Charles Darwin University; Pat Taggart, Adjunct Fellow, and Tida Nou, Project officer, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Fire-ravaged Kangaroo Island is teeming with feral cats. It’s bad news for this little marsupial

Rosemary Hohnen, Charles Darwin University and Sarah Legge, Australian National University

When I visited Kangaroo Island for the first time after the summer bushfires, I thought I knew what to expect. But what really hit me was the scale.

The wild western end of the island, once a vast mallee woodland peppered with wildflowers and mobs of roaming roos, had been completely erased. An immense dune field covered with sharp blackened sticks now stretched beyond the horizon, to the sea, hollow and quiet.

While fire is a fundamental process in many Australian ecosystems, the size and severity of this fire was extreme, and the impacts on the island’s wildlife has been immense.

For the many threatened species on Kangaroo Island, such as the critically endangered Kangaroo Island dunnart, their fight for survival still isn’t over. High numbers of feral cats roaming the landscape now pose a huge threat to their persistence, with little vegetation left within the fire scar to provide cover for wildlife.

In fact, our recent research found there are, on average, almost double the number of cats per square kilometre on Kangaroo Island than on the mainland.

The scale of the fires

Kangaroo Island is uniquely positioned, home to wildlife native to both eastern and western Australia. It protects nationally threatened species, such as the glossy black-cockatoo, the pygmy copperhead, Rosenberg’s goanna and the Kangaroo Island dunnart.

The recent bushfires on Kangaroo Island were the largest ever recorded there, destroying swathes of habitat. Over a period of 49 days the fire burnt 211,255 hectares, impacting almost half of the island, particularly the western and central regions.

For the critically endangered Kangaroo Island dunnart, the fires burnt approximately 95% of the species’ known habitat and left them on the brink of extinction.

Dunnarts face extinction

The Kangaroo Island dunnart is a small carnivorous marsupial weighing about 20 grams, with soft sooty fur and dark eyes. The species eats mainly insects, and shelters in hollow logs and in the skirts of grass trees.

Even prior to the fire the species was considered likely to become extinct in the next 20 years. Despite extensive survey efforts, the dunnart had only been seen at 19 sites on Kangaroo Island between 1990 and 2019.

Our own survey work between 2017 and 2018 confirmed the persistence of the dunnart at just six sites in the national park, with Kangaroo Island Land for Wildlife detecting several additional records on private land. All sites were in the western half of the island where the recent fires burned.

Many dunnarts are likely to have died in the fire itself, but individuals that survived are left extremely vulnerable to starvation and feral cat predation.

Cats roaming the island in big numbers

Between two and six million feral cats are estimated to live in Australia, and collectively kill more than three billion animals per year.

The problem is so large, a parliamentary inquiry is, for the first time in 30 years, investigating the impact of feral and domestic cats to native wildlife.

What’s more, in some areas on Kangaroo Island where the availability of animal carcasses is high, the density of feral cats is more than ten times as high as mainland estimates.

There are twice as many cats per square kilometre on Kangaroo Island than on mainland Australia.
Shutterstock

A high cat density poses a formidable threat to wildlife survival during the post-fire period, because cats will sometimes travel large distances to hunt within recent fire scars. Research is underway on the island to examine exactly how the fires have changed cat densities and hunting behaviour in and around burnt areas.

How to control feral cats

Controlling feral cats is one of the biggest challenges in Australian conservation. Cats are cryptic and cautious, hard to find, see, trap and remove.

Despite the challenge, a large-scale feral cat eradication is underway on Kangaroo Island. This is the largest island on which cat eradication has ever been attempted, and the project will take years.

In the meantime, feral cats are being controlled around the last refuges for Kangaroo Island dunnarts. There are multiple methods for this including shooting and cage trapping, but in remote areas that are hard to access, poison-baiting is likely to be an effective, long-term strategy.

Most feral cat baits are meat-based, but our research shows possums and bush rats are still likely to consume them.

Therefore, researchers have worked for many years on strategies to minimise the potential impacts of feral cat baits on native wildlife. For example, the poison can be delivered within a hard plastic pellet, inside the meat bait.

Field trials have indicated that while cats swallow portions of this bait whole, ingesting the pellet, most native wildlife will chew around and discard the pellet.

Hope emerges after huge survey effort

Despite the gravity of the risk to Kangaroo Island wildlife, there is hope. A huge, dedicated and effective survey effort by both government and non-government organisations has resulted in the detection of Kangaroo Island dunnarts at more than 22 sites.

Kangaroo Island dunnarts have been spotted in devastated parts of the landscape.
Jody Gates, Author provided

These small populations have been found mostly within patches of unburnt vegetation, but also – almost unbelievably – in areas that have been completely burnt.

Many of these populations appear to be very small and isolated. And now, more than ever, they’re extremely vulnerable. Targeted cat control and/or protection of vulnerable populations with exclusion fencing may be the only way to prevent their extinction.

By controlling cats, we can help native species like the Kangaroo Island dunnart get through this difficult time, and continue to fulfil their place in that wild landscape for years to come.

The authors would like to acknowledge and thank Paul Jennings, Pat Hodgens, Heidi Groffen, James Smith and Trish Mooney, for their generous contributions to this article.

Rosemary Hohnen, Adjunct associate, Charles Darwin University and Sarah Legge, Professor, Australian National University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Cats wreak havoc on native wildlife, but we’ve found one adorable species outsmarting them

Euan Ritchie, Deakin University; Amy Coetsee, University of Melbourne; Anthony Rendall, Deakin University; Tim Doherty, University of Sydney, and Vivianna Miritis, University of Sydney

Feral and pet cats are responsible for a huge part of Australia’s shameful mammal extinction record. Small and medium-sized ground-dwelling mammals are most susceptible.

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.

Long-nosed potoroos are a bit like mini kangaroos, but spend much of their time digging for fungi.
Zoos Victoria

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.

Surviving cats with a deadly game of hide and seek

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.

French Island’s thick vegetation provides potoroos with critical refuge to evade feral cats.
Vivianna Miritis

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.

Temporal activity of cats and long-nosed potoroos for winter and summer, on French Island, Victoria. Their overlap is represented by the area shaded in grey. Modified from Miritis et al. (2020).

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 expert hunters

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.

Camera traps can tell us a lot about how introduced predators and native wildlife interact.
Zoos Victoria and Deakin University

Fencing and islands can result in native animals rapidly losing their anti-predator behaviour. This can limit the success of reintroducing them to areas outside predator-free havens.

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.

Why cat eradication isn’t always the best option

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

This article is republished from The Conversation under a Creative Commons license. Read the original article.

One cat, one year, 110 native animals: lock up your pet, it’s a killing machine

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.

Cats have played a leading role in most of Australia’s 34 mammal extinctions since 1788, and are a big reason populations of at least 123 other threatened native species are dropping.

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.

More than one-quarter of Aussie households have pet cats.
Jaana Dielenberg, Author provided

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.

Surely not my cat

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.

Documented cases have included: a feather-tailed glider population in south eastern NSW; a skink population in a Perth suburb; and an olive legless lizard population in Canberra.

Urban cats

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.

The impact of roaming pet cats on Australian wildlife.

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.

What can pet owners do?

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.

A bell on a cat’s collar doesn’t stop hunting, it only makes hunting a little harder.
Wes Mountain/The Conversation, CC BY-ND

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.

Benefits of a life indoors

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).

Two cats in Western Australia stopped fairy terns from breeding.
Shutterstock

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

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Why Australia needs to kill cats

John Read, University of Adelaide and Katherine Moseby, UNSW

Introduced cats are a key threat to 123 of Australia’s threatened species.

The management of cats is challenging and divisive; many options such as rehoming, trap-neuter-release and euthanasia have been used around the world with varying success.

Australia’s recent commitment to killing 2 million feral cats to protect its native wildlife has attracted international attention and some have considered the project harsh.

While the actual target of 2 million has been rightly criticised as arbitrary and more based on public relations than rigorous science, it’s true non-lethal methods are not enough to stem the environmental havoc cats cause. Particularly in light of a UN report highlighting the world’s extinction crisis, Australia urgently needs well-targeted cat culls.

Non-lethal methods

A range of effective non-lethal methods are already protecting wildlife from cats. Cat-exclusion fences have collectively improved the conservation status of many threatened species. In addition, an increasing number of Australian councils have created progressive cat management bylaws designed to protect pet cats, wildlife and humans from the effects of free-ranging cats.

The centrepiece of many of these bylaws, supported by the vast majority of animal welfare groups, is the containment of pet cats on their owner’s property. Indoor cats live longer, safer lives than cats that are allowed to roam.

Stray cats are harder to manage. These are the cats that do not have a home, but may be directly or indirectly fed by people.

Because they are unowned, no-one is officially accountable for their health or welfare. Groups of like-minded individuals feed and even provide veterinary assistance to some of these cats, further blurring the distinction between pet and feral cats.

A trend promoted by “no kill” shelters and advocacy groups in some US states and Europe is for clowders (groups) of stray cats to be desexed, vaccinated and released back onto the streets. This process is called trap-neuter-release (TNR).

A recent RSPCA best-practice cat management discussion paper proposed a trial of TNR in Australia too – but there are very good reasons why this would be counterproductive for cat welfare.

The risks of releasing unowned cats

Informed animal welfare advocate groups, including PETA, strongly condemn the release of unowned cats, neutered or otherwise, due to the welfare risks to these cats. Human health professionals and wildlife advocates also oppose maintaining groups of cats.

Dense outdoor cat clowders are hotbeds of toxoplasmosis infections. This cat-borne disease is increasingly being linked to a range of chronic mental health conditions including schizophrenia and Alzheimer’s disease.

“No kill” groups that promote TNR erroneously claim that neutered cats significantly reduce the breeding potential of erroneously named cat “colonies”, in the same way that release of neutered mosquitoes is a proven technique for controlling disease-bearing mosquitoes.

One of us (John) has recently written a book on protecting wildlife and cats that suggests five fatal biological flaws in this logic:

Neutering mosquitoes works because impotent individuals “swamp” short-lived wild insect populations that mate only once. By contrast, female cats typically mate repeatedly when on heat, so an encounter with a neutered tom is of little consequence.
Unlike lions, domestic cats evolved as solitary hunters. While domestic cats can tolerate living in high-density clowders, they do not form hierarchical colonies, packs or prides where alpha individuals restrict the feeding, breeding or survival of subordinate animals.
Although loud cat fights might make you assume males fight over the right to exclusively mate with a female, most litters of outdoor cats are sired by multiple males. Even supposedly “dominant” males seldom intervene when another male courts a female. Neutered male cats will not protect females in their clowder from non-desexed interlopers. This means that more than 90% of cats need to be neutered to restrict population increases, an incredibly challenging proposition.
Despite the misleading label “colony”, cat clowders are not closed populations. Rather, cats typically move around to take advantage of abundant food resources. And unwanted pets are often dumped at clowder sites. The failures of several well-studied TNR programs are attributed to cats migrating or being dumped at these sites.
Despite needing repeated vaccinations to protect them from debilitating diseases, few stray cats can be captured a second time. And many can never be captured at all. This leaves them and their clowder effectively unmanageable.

TNR is biologically flawed, cruel to cats – because it returns them to a hazardous environment – and ineffective when not accompanied by high levels of adoption.

Harming marine ecosystems

Not only do predatory cats harm native wildlife, but stray or feral clowders can also directly influence marine ecosystems and fisheries.

Many commercial cat foods contain increasingly threatened predatory fish that are high in the food chain and hence use more nutrients and biological energy than plants or herbivores. US dogs and cats consume one-third of the animal-derived protein eaten by humans, with accompanying greenhouse gas emissions.

The cat food provided to stray clowders adds to this biological expense. In 2009 alone, the US-based Best Friends Animal Society, one of the major promoters of TNR, distributed over 80,000 tonnes of cat food to unowned cats. There are no similar studies in Australia, and we appear to have far lower rates of stray-cat-feeding, but it is still part of the ecological impact of stray cats.

Even more insidiously, seals, otters and dolphins in oceans around the world die from cat-borne diseases spread mainly from clowders.

Humane euthanasia

Fortunately, both science and animal welfare standards are consistent about management of cats. All healthy domestic cats for which safe homes can be found should be adopted or rehomed, then kept indoors following neutering and vaccination. All other cats, including ferals and strays that cannot be rehomed quickly, should be humanely euthanased.

Feeding or releasing cats (neutered or otherwise) threatens our wildlife and perpetuates the cycle of suffering, disease, predation and social annoyance. Non-lethal options such as feral cat-proof fencing can still be part of the solution, but euthanasia remains an important part of controlling feral and stray cats to protect our native wildlife.

Among the Pigeons: Why our cats belong indoors (2019) by John Read is published by Wakefield Press.

John Read, Associate Lecturer, Ecology and Environmental Sciences, University of Adelaide and Katherine Moseby, Research fellow, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Like cats and dogs: dingoes can keep feral cats in check

File 20190403 177175 6uzk99.jpg?ixlib=rb 1.1 — Feral cats are linked to the extinction of at least 20 Australian mammals.
Shutterstock

Mike Letnic, UNSW and Ben Feit

The role of dingoes in the Australian landscape is highly debated between ecologists, conservationists and graziers. They kill livestock, but also hunt introduced animals and keep kangaroo populations in check.

Now new research sheds more light on the benefits dingoes bring to the outback. For the first time, our research clearly shows that dingoes suppress feral cat numbers.

Our research, published recently in Ecosystems, used the world’s largest fence to compare essentially identical environments with and without dingoes. Over the course of the six-year study, dingoes drove down cat numbers – and kept them down.

Feral cats are out of control

Feral cats are a serious conservation threat. They have been linked to the extinction of at least 20 mammal species in Australia and threaten the ongoing survival of more than 100 native species.

For our study, we asked whether “top-down” pressure from dingoes (through direct killing and competition for food) had a greater influence on controlling cat numbers than “bottom-up” effects (the availability of shared food sources preyed on by cats).

Dingoes drive down the population of introduced animals.
Kim/flickr, CC BY-SA

We conducted our study by comparing the numbers of dingoes, cats and their major prey species on either side of the dingo fence in the Strzelecki Desert. The fence runs along the borders of New South Wales and South Australia and was originally built to exclude dingoes from sheep grazing lands in NSW.

The state border follows the longitude line 141 east, so the fence does not demarcate any natural boundary. It simply cuts a straight line through sand dunes with similar landforms and vegetation on either side. Thus the dingo fence provides a unique opportunity to study apex predators’ effects on ecosystems: dingoes are common on the SA side, “outside” the fence, whereas on the NSW “inside” of the fence, dingoes are rare due to intensive persecution by humans.

We collected data from sites on either side of the fence in the Strzelecki Desert, at roughly four-month intervals between 2011 and 2017. Dingo and cat scat was collected at each site, to analyse and compare diets, and spotlight searches were used to record numbers of dingoes, feral cats, as well as two of their common shared food sources: rabbits and hopping mice.

Spotlight surveys revealed dingoes to be virtually absent from study areas inside the fence, with only four dingoes recorded during the study. Where dingoes were rare inside the fence, cat numbers closely followed fluctuations of their prey species consistently over the six-year span of our study. As prey numbers increased, cat numbers also increased, and similarly as prey numbers declined, cat numbers also declined.

A feral cat in outback Australia.
Shutterstock

Outside the fence, where dingoes were common, it was quite a different story. There, cat numbers were consistently lower, with numbers of both cats and dingoes following fluctuations in prey numbers across the first two years of the study. However, from 2013 onward, dingo numbers remained high and matched trends in their prey numbers for the remainder of the study.

During this time, cat numbers remained low, and by the end of 2015, cats had virtually disappeared from our study sites outside the fence and were not recorded during spotlight surveys between November 2015 and the end of our study in July 2017.

The most likely explanation for this drastic reduction in cat populations is through interference competition – either by dingoes killing some cats or by scaring others away from habitats in which they would usually hunt. Indeed, we occasionally found cat remains in dingo scats, which suggests dingoes prey on cats.

Although our scat analyses indicated that dingoes and cats eat similar foods, there was no evidence that competition for food was a major factor in how dingoes reduce cat populations. This is because prey were plentiful outside the fence, where dingoes were common and cats were rare.

This research show how dingoes can help conservation efforts by suppressing feral cat populations. It adds to previous work showing dingoes are important in maintaining healthy ecosystems, as they reduce and eradicate feral herbivores like pigs and goats, and stop kangaroos from overpopulating districts.

This article was updated on April 5 to credit Ben Feit as a co-author.

Mike Letnic, Professor, Centre for Ecosystem Science, UNSW and Ben Feit, Post-doctoral researcher

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Could Tassie devils help control feral cats on the mainland? Fossils say yes

File 20190222 195876 1pvj44l.jpg?ixlib=rb 1.1 — The Tasmanian devil once thrived on mainland Australia.
Shutterstock/mastersky

Michael Westaway, Griffith University and Gilbert Price, The University of Queensland

The Tasmanian devil – despite its name – once roamed the mainland of Australia. Returning the devil to the mainland may not only help its threatened status but could help control invasive predators such as feral cats and foxes.

The idea of returning devils to the mainland has been raised before.

But now we’ve explored the idea from a palaeontological view. We looked at the fossil record of mainland devils, in a paper published online and in print soon in the journal Biological Conservation.

A well preserved devil mandible (lower jaw) recovered from excavations west of Townsville.
Gilbert Price, Author provided

The fossil record helps us better understand how the devils co-existed on mainland Australia with other wildlife. It also helps us see how these iconic animals may possibly interact with small and medium-sized animals if reintroduced to the mainland in the future.

Back in the wild

Ecologists have reintroduced several apex predators to environments where they were once driven to localised extinction. This has helped restore past ecosystems by providing a clearer ecological balance.

One of the best-known examples is the reintroduction of wolves to Yellowstone National Park in the United States, to check the overgrazing and destruction of habitat by elk.

By reintroducing Tasmanian devils into mainland Australia, can we possibly help restore ecological systems that support devils along with small to medium-sized native mammals?

Native and exotic predators

Tasmanian devils and thylacines (Tasmanian tigers) were displaced across the mainland of Australia sometime after the dingo was introduced from southeast Asia at least 3,500 years ago.

But these iconic Australian predators were still able to survive in Tasmania. The island was created 10,000 years ago by rising sea levels, well before the arrival of dingoes on mainland Australia.

Dingoes have now been eradicated across much of mainland Australia, particularly within the seclusion zone of the dingo fence in the southeast of the continent. The 5,400km fence stretches eastwards across South Australia into New South Wales and to southeast Queensland.

Exotic predators such as foxes and cats now thrive across many parts of Australia, and have devastating impacts on small to medium-sized Australian mammals.

But until recently they have not been able to gain a foothold in Tasmania. Many ecologists believe the presence of the devil has prevented these other animals making their destructive mark on the ecology of Tasmania.

Sadly the situation is changing as a result of the deadly devil facial tumour disease, an infectious cancer that has destroyed many populations of Tasmanian devils. Estimates range up to 90% of some population groups now wiped out.

As a result, feral cats are now moving into former devil habitats and hunting native species on Tasmania.

A fossil window to the past

So what does the fossil record tell us about the past life of the Tasmanian devil in mainland Australia?

The Willandra Lakes World Heritage Area, in southeast Australia, provides an extraordinary archaeological and palaeoecological record of Ice Age Australia.

Recovery of fossils and devil coprolites from eroding bettong burrows at the Willandra Lakes World Heritage Area.
Michael Westaway, Author provided

In the past, skeletal remains buried within the landscape were commonly fossilised. Evidence of small animals that dug burrows (such as burrowing bettongs) and the predators that pursued them in their burrows, are exceptionally well preserved.

Our excavations reveal how devils and other small-to-medium sized mammals and reptiles interacted over more than 20,000 years in this area. Even during the peak arid phase, known as the Last Glacial Maximum, it seems that devils and their prey successfully co-existed.

The fossil record (10,000 to 4,000 years ago): This shows the fauna reference condition prior to the arrival of the dingo. (1 Western Quoll, 2 Tasmanian Devil, 3 Thylacine, 4 Bilby, 5 Western Barred Bandicoot, 6 Southern Brown Bandicoot, 7 Burrowing Bettong, 8 Brush Tailed Bettong, 9 Wombat, 10 Nail-Tailed Wallaby, 11 Hare Wallaby, 12 Western and Eastern Grey Kangaroo, 13 Red Kangaroo, 14 Crest Tailed Mulgara, 15 Greater Stick Nest Rat, 16 Hopping Mouse, 17 Fox, 18 Cat, 19 Rabbit)
Toot Toot Design, Author provided

The contemporary record: This shows today’s situation in the Willandra Lakes World Heritage Area. Light grey animals represent those animals that are now locally extinct.
Toot Toot Design, Author provided

The fossil record shows that the range of habitats occupied by devils in the past was far more diverse than today, with populations being found across environments from the central arid core to the northern tropics.

This suggests that devils today should, theoretically, be able to reoccupy a similarly extensive range of habitats.

Former devil range across Australia as revealed by the known fossil record.
Toot Toot Design, Author provided

Better the devil you know

Some ecologists suggest dingoes should be reintroduced into Australian habitats in order to reduce the impact of cats and foxes on native mammals.

One problem is that dingoes also prey on livestock. This is the reason the dingo fence was constructed during the 1880s.

But devils are not active predators of cattle and sheep. So reintroducing a predator that has a much longer evolutionary history with other native mammals in this country would likely receive far less opposition from pastoralists.

A reintroduction of devils back to the mainland may be a new approach to consider for controlling the relentless, destructive march of exotic predators and restore crucial elements of Australia’s biodiversity.

It still needs to be demonstrated that devils can suppress the activities of cats and foxes on the mainland, as they seem to have done in Tasmania. Experiments with devils in a range of different settings would help to establish this.

A new research approach involving palaeontologists, conservation biologists and policy makers may help us understand how we can restore biodiversity function in Australia.

Michael Westaway, Senior Research Fellow, Australian Research Centre for Human Evolution, Griffith University and Gilbert Price, Lecturer in Palaeontology, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Feral cat cull: why the 2 million target is on scientifically shaky ground

File 20190217 56243 jbdoqp.jpg?ixlib=rb 1.1 — The government’s target to kill 2 million feral cats sounds impressive, but lacks scientific rigour.
Author provided

Tim Doherty, Deakin University; Dale Nimmo, Charles Sturt University; Don Driscoll, Deakin University; Euan Ritchie, Deakin University, and Ricky Spencer, Western Sydney University

The Australian government’s target of killing 2 million feral cats by 2020 attracted significant public interest and media attention when it was unveiled in 2015.

But in our new research, published today in Conservation Letters, we explain why it has a shaky scientific foundation.

The target was developed for the Threatened Species Strategy. At the time of its launch in 2015, there was no reliable estimate of the size of Australia’s feral cat population. Figures of between 5 million and 18 million were quoted, but their origin is murky: it’s possible they came from a single estimate of feral cat density in Victoria, extrapolated across the continent.

A recent review estimated a much smaller population size — probably varying from 2 million to 6 million, depending on environmental conditions. Using this estimate, the proportion of Australia’s cat population to be killed under the government’s target is now likely in the range 32-95%, rather than 11-40% based on the original population estimate.

Targets for the removal of pest animals should consider how they will affect an animal’s current and future population size. But because a scientific justification for the 2 million target was never provided, it is unclear whether or how the revised estimate would alter the target.

Feral cats culled in Queensland.
http://www.couriermail.com.au/news/queensland/news-story/746d8ad0366fe9f64ea9c26d36a41a37

Hitting the target, missing the point

For cat control to have a lasting effect on feral populations, it needs to be intense, sustained, and carried out over large areas. This is because cats can rapidly reproduce and re-invade areas. To benefit threatened species, cat control also needs to be undertaken in areas that contain — or could potentially contain — native species that are threatened by cats.

Research commissioned by the government conservatively estimated that around 211,500 feral cats were killed in 12 months in 2015–16 (ranging between around 135,500 and 287,600). This estimate was used to report that the first-year target to kill 150,000 cats was met with room to spare.

The benefit to threatened species of achieving this target is unclear, because we don’t know if the control efforts had a measurable effect on cat populations; whether they took place in areas that would benefit threatened species; or how (or if) the target and related activities contributed to the estimated 211,500 cat deaths.

Around 75% of the killed cats were attributed to shooting by farmers and hunters. It is questionable whether such approaches could keep pace with high rates of population growth and re-invasion from surrounding areas.

These and other issues were known before the target was set, leading experts to recommend that an overall cat culling target should not be set.

Cat image captured using camera traps in the Hawkesbury region, NSW.
Western Sydney University

Shifting focus

The focus on killing cats risks distracting attention from other threats to native wildlife. These threats include habitat loss, which has been largely overlooked in the Threatened Species Strategy.

Habitat loss is politically sensitive because its main driver is the clearing of land to make way for economic activities such as agriculture, urban development, and mining. The strategy mentions feral cats more than 70 times, but habitat loss is mentioned just twice and land clearing not at all. Australia has one of the world’s worst rates of land clearing, which has recently increased in some regions. For instance, clearing of native vegetation in New South Wales rose by 800% between 2013 and 2016.

A focus on feral cats is warranted, but not at the expense of tackling other conservation threats too. A comprehensive, integrated approach towards threatened species conservation is essential.

Any upside?

Despite its questionable scientific basis, it is possible that the ambitious nature of the 2 million target has raised the public profile of feral cats as a conservation issue. However, to our knowledge, there has been no attempt to measure the effectiveness of the target in raising awareness or changing attitudes, and so this remains a hypothetical proposition.

Raising awareness about the negative impacts of cats on native wildlife is important.

The Threatened Species Strategy has other targets that are more closely linked to conservation outcomes, such as the eradication of cats from five particular islands and the establishment of ten new fenced cat-free exclosures. Achieving these targets will make a small contribution to the culling target, but have a comparatively large benefit for some threatened species.

Australia’s target to kill 2 million feral cats is a highly visible symbol of a broader campaign, but the success of policies aimed at reducing the impacts of feral cats should focus squarely on the recovery of native species.

Tim Doherty, Research Fellow, Deakin University; Dale Nimmo, Associate professor/ARC DECRA fellow, Charles Sturt University; Don Driscoll, Professor in Terrestrial Ecology, Deakin University; Euan Ritchie, Associate Professor in Wildlife Ecology and Conservation, Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University, and Ricky Spencer, Associate Professor of Ecology, Western Sydney University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Tassie devils’ decline has left a feast of carrion for feral cats

File 20181127 76737 frgu15.jpg?ixlib=rb 1.1 — Healthy Tasmanian devil populations have cornered the market on carrion.
Menna Elizabeth Jones, Author provided

Calum Cunningham, University of Tasmania; Christopher Johnson, University of Tasmania; Menna Elizabeth Jones, University of Tasmania, and Tracey Hollings, University of Melbourne

The decline of Tasmanian devils is having an unusual knock-on effect: animal carcasses would once have been gobbled up in short order by devils are now taking many days longer to disappear.

We made the discovery, published today in the journal Proceedings of the Royal Society B, by placing carcasses in a range of locations and watching what happened. We found that reduced scavenging by devils results in extra food for less efficient scavengers, such as feral cats.

Tasmanian devils have struggled for two decades against a typically fatal transmissible cancer, called devil facial tumour disease. The disease has caused devil populations to plummet by about 80% on average, and by up to 95% in some areas.

DFTD has spread across most of Tasmania over a 20-year period. Dashed lines show the estimated disease front.
Calum Cunningham/Menna Jones

Scavengers are carnivores that feed on dead animals (carrion). Almost all carnivores scavenge to a greater or lesser degree, but the devil is Tasmania’s dominant scavenger. Since the extinction of the Tasmanian tiger, it is also the island’s top predator.

A scavenging experiment

In our study, we put out carcasses of the Tasmanian pademelon (a small wallaby weighing roughly 5kg) in a variety of places, ranging from disease-free areas with large devil populations, to long-diseased areas where devil numbers are very low. We then used motion-sensor cameras to record all scavenger species that fed on the carcasses.

The Carnivores of Tasmania: a Scavenging Experiment.

Unsurprisingly, much less carrion was consumed by devils in areas where devil populations have declined. This has increased the availability of carrion for other species, such as the invasive feral cat, spotted-tailed quoll, and forest raven. All of these species significantly increased their scavenging in places with fewer devils.

Consumption of experimentally placed carcasses.
Proceedings of the Royal Society B

The responses of native scavengers (quolls and ravens) were subtly different to those of feral cats. The amount of feeding by quolls and ravens depended simply on how much of each carcass had already been consumed by devils. Ravens and quolls are smaller and less efficient than devils at consuming carcasses, so they get the chance to feed only when devils have not already monopolised a carcass.

In contrast, feral cats tended to scavenge only at sites where devils were at very low abundance. This suggests that healthy devil populations create a “landscape of fear” that causes cats to avoid carcasses altogether in areas where they are likely to encounter a devil. It seems that the life of a feral cat is now less scary in the absence of devils.

Predator prevalence

By looking at 20 years of bird surveys from BirdLife Australia, we also found that the odds of encountering a raven in Tasmania have more than doubled from 1998 to 2017. However, we were unable to directly link this with devil declines. It is likely the raven population is growing in response to a range of factors that includes land-use change and agricultural intensification, as well as reduced competition with devils.

Other studies have shown that cats have also become more abundant in areas where devils have declined. This highlights the potential for devils to act as a natural biological control on cats. Cats are a major threat to small native animals and are implicated in most Australian mammal extinctions.

Carcass concerns

Although smaller scavengers consumed more carrion as devils declined, they were unable to consume them as rapidly as devils. This has resulted in the accumulation of carcasses that would previously have been quickly and completely eaten by devils.

In places with plenty of devils, carcasses were completely eaten within an average of five days, compared with 13 days in places where devil facial tumour disease is rife. That means carcasses last much longer where devils are rare.

Around 2 million medium-sized animals are killed by vehicles or culled in Tasmania each year, and most are simply left to decompose where they fall. With devils consuming much less carrion, it is likely that carcasses are accumulating across Tasmania. It is unclear how much of a disease risk they pose to wildlife and livestock.

Conserving carnivores

Large carnivores are declining throughout the world, with knock-on effects such as increasing abundance of smaller predators. In recent years, some large carnivores have begun returning to their former ranges, bringing hope that their lost ecological roles may be restored.

Carnivores are declining for many reasons, but an underlying cause is that humans do not necessarily appreciate their pivotal role in the health of entire ecosystems. One way to change this is to recognise the beneficial services they provide.

Our research highlights one of these benefits. It supports arguments that we should help the devil population recover, not just for their own sake but for other species too, including those threatened by feral cats.

The devil seems to be solving the disease problem itself, rapidly evolving resistance to facial tumours. Any management plan will need to help this process, and not hinder it. Potentially, returning devils to mainland Australia could provide similar benefit to wildlife threatened by feral predators.

Calum Cunningham, PhD candidate, University of Tasmania, University of Tasmania; Christopher Johnson, Professor of Wildlife Conservation and ARC Australian Professorial Fellow, University of Tasmania; Menna Elizabeth Jones, Associate professor, University of Tasmania, and Tracey Hollings, Senior Scientist, Ecological Modelling at Arthur Rylah Institute for Environmental Research, and Honorary Research Fellow, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Non-lethal methods

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Harming marine ecosystems

Humane euthanasia

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Feral cats are out of control

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Back in the wild

Native and exotic predators

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Better the devil you know

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Hitting the target, missing the point

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A scavenging experiment

Predator prevalence

Carcass concerns

Conserving carnivores

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