How to know if we’re winning the war on Australia’s fire ant invasion, and what to do if we aren’t


Fire ants like these can give a nasty bite.
Shutterstock/SweetCrisis

Daniel Spring, University of Melbourne and Jonathan Keith, Monash University

More than A$400 million of government funding is being invested in the latest round of the fire ant program in the hope of eradicating the invasive pests by 2027.

But recent reports on the ABC suggest the invasion is spreading beyond containment lines in south-east Queensland, and there are delays in responding to public reports of new ant infestations.

The claims are denied by Graeme Dudgeon, the new general manager of Queensland Government’s National Red Imported Fire Ant Eradication Program.




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Fire ants are native to South America but nests were first discovered in Brisbane in 2001. It’s thought they arrived via shipping at the Port of Brisbane.

They’re regarded as one of the world’s worst invasive species and have a painful bite which is why the Queensland Government has been trying to wipe them out here.

Is eradication possible?

An independent review in 2016 found the fire ants were confined to a region of south east Queensland and said there was an opportunity to eradicate the pests.

But the latest debate raises the question of whether eradication is the best plan, or would further containing the spread of the fire ants be a more practicable solution?

To achieve its aim of eradicating the fire ant problem, the program needs to progressively shrink the invasion.

If the invasion is shrinking too slowly (or is expanding), eradication won’t be achieved by 2027. Without ongoing monitoring of the invasion’s size, the program might be failing without the general public knowing.

But knowing the fire ant invasion’s size isn’t easy because there isn’t enough funding to survey all locations that might have them.

Estimates of the invasion

Using records of past fire ant detections, we have demonstrated how to estimate the invasion’s size when only part of the managed area is surveyed.

Our inference of the boundary of the fire ant invasion in April 2015. The different coloured polygons correspond to different levels of credibility that the boundary contains the invasion, with the outermost boundary corresponding to the highest credibility. Small crosses represent sites where nests have been detected, with the most recent detections in red and the oldest in brown.
Nature/Authors provided, CC BY

If this approach to estimating the invasion boundary is applied each year during the current program, we could estimate whether the invasion is shrinking fast enough to be gone by 2027.

The importance of this issue demands a rigorous scientific analysis using transparent data and methods. Without this, anecdotal evidence that the current invasion is spreading is all we have to indicate whether eradication efforts are failing.

The size of the fire ant invasion should not only be measured in terms of the total area within its estimated boundary but also the density of nests within this area.

Eradication won’t be achieved if both the invasion boundary and the density within it are increasing. This straightforward test to determine whether the program is failing has not yet been applied.

But such a test could be done if updated records of the fire ant invasion are regularly made available to allow for periodic estimation of updated maps of the invasion.

Never give up

Even if eradication by 2027 is unlikely, this does not mean we should give up, provided future control efforts can contain the invasion at an affordable cost.

If the current program fails to eradicate the fire ants, it may still set the stage for effective long-term containment of the invasion.

A poor outcome will result if current management efforts are spread thinly over the infested area, reducing the density of nests but not eradicating them from any suburbs.

A better outcome would involve shrinking the infested area, that is, eradicating the ants from many or most suburbs, so that subsequent containment efforts can focus resources on a smaller area.

Is it still early enough in Australia to shrink the fire ant invasion to a manageably small area and thereby protect most homes and most of the environment for a long time? The required information to answer this question is not yet available.




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But if Queensland’s eradication program has substantially slowed the spread so far, this provides confidence that continuing the program could effectively suppress the invasion. If so, we need to estimate what it will cost to keep out fire ants from most homes and most of the environment for a long time.

It’s often claimed that removing the last 1% of invaders costs as much as removing the previous 99%. If the current program removes all ants from most areas by 2027, this may provide large benefits without the extra cost of finding the last few ants in all infested areas.

Even if we do eradicate fire ants this time, it’s almost certain they will be back because they can readily hitchhike rides on ships.

So if governments can keep fire ant numbers down through ongoing containment, a lot of people and a lot of native species will benefit.The Conversation

Daniel Spring, Research Fellow, School of Biosciences, University of Melbourne and Jonathan Keith, Associate Professor, School of Mathematical Sciences, Monash University

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

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Making deer fair game for unlicensed hunting is the right step for New South Wales


The fate of deer carcasses is a crucial consideration in monitoring the success of future culling.
Emma Spencer, Author provided

Thomas Newsome, University of Sydney and Emma Spencer, University of Sydney

The New South Wales government last week revealed plans to ease shooting restrictions on feral deer. If the plans go ahead, deer will be stripped of their status as a game animal and will no longer be afforded protection under the state’s animal control laws.

This will mean that a game hunting licence would not be required for recreational, commercial and professional hunting of deer species. Restrictions on how and when deer can be hunted would also be lifted.

Feral deer will be treated the same as other pest animals in NSW, including red foxes, feral cats and rabbits.

Deer are already considered a pest

Last year the NSW government approved 11 regional pest animal plans, each of which declared deer as a priority pest species. Several hunting regulations have already been suspended to manage abundant deer populations, and in February 2019 the government announced a A$9 million deer control program described as the most extensive of its kind.




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Removing the game status of deer is the next logical step towards controlling existing deer numbers in NSW, and slowing their spread to new areas. Deer currently cover 17% of NSW, and this area has more than doubled since 2009.

Deer now cover 17% of NSW.
NSW Dept of Primary Industries

Without urgent and effective control, the deer population could spread throughout the entire state and beyond.

Effective control is needed to stop the spread of feral deer in Australia.
Emma Spencer

The impacts of deer

Feral deer remain one of Australia’s least studied introduced mammals. Yet the evidence shows they have a substantial impact on Australia’s ecosystems and agriculture.

Since 2005, grazing and environmental damage by feral deer has been listed as a key threatening process under NSW legislation. Deer are known to graze on threatened plant species, and also cause erosion and soil compaction. They damage pasture; destroy fences and contaminate water sources; harm trees via antler rubbing; rip up the ground during rutting season; and potentially contribute to the spread of livestock diseases.

Deer are a threat to humans too. The Illawarra region south of Sydney, a hotspot for deer activity, has seen one death and multiple serious injuries between 2003 and 2017 due to vehicle collisions with deer.

Deer can also carry pathogens that cause human disease such as Leptospirosis and Cryptosporidium.

Choosing the right control method

Ground-based shooting is the main way to manage deer in the urban fringes, regional areas and national parks. Unfortunately, coordinated ground shoots have only been effective for areas of less than 1,000 hectares, and there is no evidence that uncoordinated shooting by recreational hunters actually works to control deer on a widespread basis.

Aerial shooting can potentially be more successful over large tracts of land, but may not be a good option when tree cover is high and visibility is low. Poison baiting could help, although there is no method available to deliver baits safely, effectively and specifically to deer.

Irrespective of the control method, a coordinated approach is needed. We need a strategy that not only controls deer where damage is worst, but also prevents their spread to new areas. This will require NSW to work closely with the ACT and Victoria.

A red fox feeds on a culled feral deer.
Emma Spencer

Rigorous monitoring will also be vital. This is important to gauge success (how many deer were culled, and the ethics of shooting, trapping and baiting), and to determine whether the control efforts have unintended impacts on the environment, such as deer carcasses providing food for scavenging pests.




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Scavenging pests have been observed feeding on carcasses, but whether culling deer and other feral animals actually increases their abundance and impacts is unknown. Carcasses also provide a source of food for native scavengers such as eagles and ravens, and are integral to the structure and function of ecosystems.

The negative and positive impacts of deer culling on the broader ecosystem therefore needs consideration when developing and implementing monitoring plans. NSW can be the leader in this regard, starting from day one after removing the status of the deer as a game species.The Conversation

Thomas Newsome, Lecturer, University of Sydney and Emma Spencer, PhD candidate, University of Sydney

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

Invasive species are Australia’s number-one extinction threat



Barking Owls are one of Australia’s 1,770 threatened or endangered species.
Navin/Flickr, CC BY-SA

Andy Sheppard, CSIRO and Linda Broadhurst, CSIRO

This week many people across the world stopped and stared as extreme headlines announced that one eighth of the world’s species – more than a million – are threatened with extinction.

According to the UN report from the Intergovernmental Science-Policy Platform for Biodiversity and Ecosystem Services (IPBES) which brought this situation to public attention, this startling number is a consequence of five direct causes: changes in land and sea use; direct exploitation of organisms; climate change; pollution; and invasion of alien species.




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It’s the last, invasive species, that threatens Australian animals and plants more than any other single factor.

Australia’s number one threat

Australia has an estimated 600,000 species of flora and fauna. Of these, about 100 are known to have gone extinct in the last 200 years. Currently, more than 1,770 are listed as threatened or endangered.

While the IPBES report ranks invasive alien species as the fifth most significant cause of global decline, in Australia it is a very different story.

Australia has the highest rate of vertebrate mammal extinction in the world, and invasive species are our number one threat.

Cats and foxes have driven 22 native mammals to extinction across central Australia and a new wave of decline – largely from cats – is taking place across northern Australia. Research has estimated 270 more threatened and endangered vertebrates are being affected by invasive species.

Introduced vertebrates have also driven several bird species on Norfolk Island extinct.

The effects of invasive species are getting worse

Although Australia’s stringent biosecurity measures have dramatically slowed the number of new invasive species arriving, those already here have continued to spread and their cumulative effect is growing.

Recent research highlights that 1,257 of Australia’s threatened and endangered species are directly affected by 207 invasive plants, 57 animals and three pathogens.

These affect our unique biodiversity, as well as the clean water and oxygen we breath – not to mention our cultural values.

When it comes to biodiversity, Australia is globally quite distinct. More than 70% of our species (69% of mammals, 46% of birds and 93% of reptiles) are found nowhere else on earth. A loss to Australia is therefore a loss to the world.

Some of these are ancient species like the Wollemi Pine, may have inhabited Australia for up to 200 million years, well before the dinosaurs.




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But invasive species are found in almost every part of Australia, from our rainforests, to our deserts, our farms, to our cities, our national parks and our rivers.

The cost to Australia

The cost of invasive species in Australia continue to grow with every new assessment.

The most recent estimates found the cost of controlling invasive species and economic losses to farmers in 2011-12 was A$13.6 billion. However this doesn’t include harm to biodiversity and the essential role native species play in our ecosystems, which – based on the conclusions of the IPBES report – is likely to cost at least as much, and probably far more.

Rabbits, goats and camels prevent native desert plant community regeneration; rabbits alone impacting over 100 threatened species. Rye grass on its own costs cereal farmers A$93M a year.

Aquaculture diseases have affected oysters and cost the prawn industry $43M.

From island to savannah

Globally, invasive species have a disproportionately higher effect on offshore islands – and in Australia we have more than 8,000 of these. One of the most notable cases is the case of the yellow crazy ants, which killed 15,000,000 red land crabs on Christmas Island.




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Nor are our deserts immune. Most native vertebrate extinctions caused by cats have occurred in our dry inland deserts and savannas, while exotic buffel and gamba grass are creating permanent transformation through changing fire regimes.

Australia’s forests, particularly rainforests, are also under siege on a number of fronts. The battle continues to contain Miconia weed in Australia – the same weed responsible for taking over 70% of Tahiti’s native forests. Chytrid fungus, thought to be present in Australia since 1970, has caused the extinction of at least four frog species and dramatic decline of at least ten others in our sensitive rainforest ecosystems.

Myrtle rust is pushing already threatened native Australian Myrtaceae closer to extinction, notably Gossia gonoclada, and Rhodamnia angustifolia and changing species composition of rainforest understories, and Richmond birdwing butterfly numbers are under threat from an invasive flower known as the Dutchman’s pipe.

Australia’s rivers and lakes are also under increasing domination from invasive species. Some 90% of fish biomass in the Murray Darling Basin are European carp, and tilapia are invading many far north Queensland river systems pushing out native species .

Invasive alien species are not only a serious threat to biodiversity and the economy, but also to human health. The Aedes aegypti mosquito found in parts of Queensland is capable of spreading infectious disease such as dengue, zika, chikungunya and yellow fever.

And it’s not just Queensland that is under threat from diseases spread by invasive mosquitoes, with many researchers and authorities planning for when, not if, the disease carrying Aedes albopictus establishes itself in cooler and southern parts of Australia.




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What solutions do we have?

Despite this grim inventory, it’s not all bad news. Australia actually has a long history of effectively managing invasive species.

Targeting viruses as options for controlling rabbits, carp and tilapia; we have successfully suppressed rabbit populations by 70% in this way for 50 years.

Weeds too are successful targets for weed biological control, with over a 65% success rate controlling more than 25 targets.

The IPBES report calls for “transformative action”. Here too Australia is at the forefront, looking into the potential of gene-technologies to suppress pet hates such as cane toads.




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Past and current invasive species programs have been supported by governments and industry. This has provided the type of investment we need for long-term solutions and effective policies.

Australia is better placed now, with effective biosecurity policies and strong biosecurity investment, than many countries. We will continue the battle against invasive species to stem biodiversity and ecosystem loss.The Conversation

Andy Sheppard, Research Director CSIRO Health & Biosecurity, CSIRO and Linda Broadhurst, Director, Centre for Australian National Biodiversity Research, CSIRO

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.




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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.




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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:

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.




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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.The Conversation

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.

How indigenous expertise improves science: the curious case of shy lizards and deadly cane toads



File 20190408 2901 1tbo2ex.jpg?ixlib=rb 1.1
The Balanggarra Rangers are land management representatives of the Balanggarra people, the indigenous traditional owners of the East Kimberley. (L-R) Wes Alberts, Bob Smith (coordinator) James ‘Birdy’ Birch, Isiah Smith, Quentin Gore.
The Kimberley Land Council, Author provided

Georgia Ward-Fear, University of Sydney and Rick Shine, University of Sydney

It’s a common refrain – western ecologists should work closely with indigenous peoples, who have a unique knowledge of the ecosystems in their traditional lands.

But the rhetoric is strong on passion and weak on evidence.

Now, a project in the remote Kimberley area of northwestern Australia provides hard evidence that collaborating with Indigenous rangers can change the outcome of science from failure to success.




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Fighting a toxic invader

This research had a simple but ambitious aim: to develop new ways to save at-risk predators such as lizards and quolls from the devastating impacts of invasive cane toads.

Cane toads are invasive and highly toxic to Australia’s apex predators.
David Nelson

All across tropical Australia, the arrival of these gigantic alien toads has caused massive die-offs among meat-eating animals such as yellow-spotted monitors (large lizards in the varanid group) and quolls (meat-eating marsupials). Mistaking the new arrivals for edible frogs, animals that try to eat them are fatally poisoned by the toad’s powerful toxins.

Steep population declines in these predators ripple out through entire ecosystems.

But we can change that outcome. We expose predators to a small cane toad, big enough to make them ill but not to kill them. The predators learn fast, and ignore the larger (deadly) toads that arrive in their habitats a few weeks or months later. As a result, our trained predators survive, whereas their untrained siblings die.




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Conservation ‘on Country’

But it’s not easy science. The site is remote and the climate is harsh.

We and our collaborators, the Western Australian Department of Biodiversity, Conservation and Attractions, decided at the outset that we needed to work closely with the Indigenous Traditional Owners of the east Kimberley – the Balanggarra people.

So as we cruised across the floodplain on quad bikes looking for goannas, each team consisted of a scientist (university-educated, and experienced in wildlife research) and a Balanggarra Indigenous ranger.

Although our study species is huge – a male yellow-spotted monitor can grow to more than 1.7 metres in length and weigh more than 6kg – the animals are well-camouflaged and difficult to find.

Over an 18-month study, we caught and radio-tracked more than 80 monitors, taught some of them not to eat toads, and then watched with trepidation as the cane toad invasion arrived.




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Excitingly, the training worked. Half of our trained lizards were still alive by the end of the study, whereas all of the untrained lizards died soon after toads arrived.

That positive result has encouraged a consortium of scientists, government authorities, conservation groups, landowners and local businesses to implement aversion training on a massive scale (see www.canetoadcoalition.com), with support from the Australian Research Council.

A yellow-spotted monitor fitted with a radio transmitter in our study. This medium-sized male was trained and lived for the entirety of the study in high densities of cane toads.
Georgia Ward-Fear, University of Sydney



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Cross-cultural collaboration key to success

But there’s a twist to the tale, a vindication of our decision to make the project truly collaborative.

When we looked in detail at our data, we realised that the monitor lizards found by Indigenous rangers were different to those found by western scientists. The rangers found shyer lizards, often further away from us when sighted, motionless, and in heavy cover where they were very difficult to see.

Gregory Johnson, Balanggarra elder and ranger.
Georgia Ward-Fear

We don’t know how much the extraordinary ability of the rangers to spot those well-concealed lizards was due to genetics or experience – but there’s no doubt they were superb at finding lizards that the scientists simply didn’t notice.

And reflecting the distinctive “personalities” of those ranger-located lizards, they were the ones that benefited the most from aversion training. Taking a cautious approach to life, a nasty illness after eating a small toad was enough to make them swear off toads thereafter.

In contrast, most of the lizards found by scientists were bold creatures. They learned quickly, but when a potential meal hopped across the floodplain a few months later, the goanna seized it before recalling its previous experience. And even holding a toad briefly in the mouth can be fatal.

Comparisons of conditions under which lizards were initially sighted in the field by scientists and Indigenous rangers (a) proximity to lizards in metres (b) density of ground-cover vegetation (>30cm high) surrounding the lizard (c) intensity of light directly on lizard (light or shade) (d) whether the lizard was stationary or moving (i.e. walking or running). Sighting was considered more difficult if lizards were further away, in more dense vegetation, in shade, and stationary.
Georgia Ward-Fear, University of Sydney

As a result of the intersection between indigenous abilities and lizard personalities, the overall success of our project increased as a result of our multicultural team.

If we had just used the conventional model – university researchers doing all of the work, indigenous people asked for permission but playing only a minor role – our project could have failed, and the major conservation initiative currently underway may have died an early death.

So our study, now published in Conservation Letters, provides an unusual insight – backed up by evidence.

Moving beyond lip service, and genuinely involving Indigenous Traditional Owners in conservation research, can make all the difference in the world.

Georgia Ward-Fear (holding a yellow-spotted monitor) with Balanggarra Rangers Herbert and Wesley Alberts.
David Pearson, WA Department of Biodiversity, Conservation and Attractions

This research was published in collaboration with James “Birdy” Birch and his team of Balanggarra rangers in the eastern Kimberley.The Conversation

Georgia Ward-Fear, Post doctoral fellow and Conservation Ecologist , University of Sydney and Rick Shine, Professor in Evolutionary Biology, University of Sydney

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.




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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.




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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.




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Why do some graziers want to retain, not kill, dingoes?


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.The Conversation

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.

Invasive ants: federal budget takes aim but will it be a lethal shot?



File 20190404 131415 1ag8r2w.jpg?ixlib=rb 1.1
Argentine ants are a fact of life in many parts of Australia, but can still potentially be banished from Norfolk Island.
Davefoc/Wikimedia Commons, CC BY-SA

Lori Lach, James Cook University

Amid all the usual items we expect to see in the federal budget was one that raised eyebrows: A$28.8 million for three ant eradication programs.

Yet amid the inevitable media puns about the government “upping the ant-e”, we should note that these funds are for the continuation of existing programs that have already attracted significant funding and made substantial progress. Stopping now would have meant previous funding was wasted.

The funds will go a long way towards protecting Australia’s economy and environment from the damage wrought by invasive ants. But despite the apparent cash splurge, it nevertheless falls short of what is really needed.

Of the $28.8 million, $18.3 million was for the National Red Imported Fire Ant Eradication Program. These funds are part of a $411 million, ten-year program begun in 2017 to eradicate red imported fire ants from southeast Queensland, the only place they are found in Australia.




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Cannibalism helps fire ants invade new territory


Removing these pests will avoid an estimated $1.65 billion in total costs to 19 different parts of the economy. With previous funding, the program eradicated these ants from 8,300 hectares near the Port of Brisbane, making it the world’s largest ant eradication to date.

The Yellow Crazy Ant Eradication Program was allocated $9.2 million over three years. Yellow crazy ants have caused a cascade of ecological effects on Christmas Island, and at their peak abundance temporarily blinded a Queensland cane farmer with their acid spray.

The Wet Tropics Management Authority, which runs the program, had requested $6 million per year for six years to continue removing the ant from in and around the Wet Tropics World Heritage Area. The federal funding is $3 million short of this, and the authority is still waiting to hear whether the Queensland government will provide the remainder.

Since 2013, the program has received $9.5 million from the federal government (and $3 million from the Queensland government). No yellow crazy ants have been observed in about half of the target area in more than a year. A yet-to-be published analysis estimates the benefit-cost ratio for the program as 178:1.

“It’s a mop-up operation… we’ve got our foot on the throat of this thing.”

A further $1.3 million was allocated to the Argentine Ant Eradication Strategy on Norfolk Island in the South Pacific. Argentine ants have invaded places with Mediterranean-type climates all over the world, including southwestern Western Australia and parts of southern Australia, and become firmly established. But unlike those areas, the population on Norfolk Island is still considered small enough to be eradicable, and federally funded efforts to remove them began in 2010.

Yellow crazy ants in Queensland and Argentine ants on Norfolk Island directly threaten World Heritage Areas. The ants can have significant impacts on native birds, mammals, insects, reptiles, amphibians, and plants. Getting rid of them is important for meeting Australia’s international obligations to protect World Heritage sites.

What is ant eradication?

Ant eradication means removing all individuals of a particular ant species from a given area.

The first step is to define the extent of that area. Depending on the species, this may involve visual searches and/or placing lures such as sausages, cat food, or jam to attract the ants. The public can help by notifying relevant authorities of unusual ants in their gardens, and by not transporting materials that have ants on them.

The second step is treatment. Currently, the only way to eradicate ants is with insecticidal baits. Ants’ social structure makes this particularly challenging: killing the queens is vital for eradication, but queens typically stay sheltered in the nest – the only ants we see out foraging are workers.

Some of the most problematic ant species can have hundreds of queens and tens of thousands of workers per nest. They can reach extraordinarily high densities, partly because invasive ant species, unlike most of our native ant species, do not fight one another for territories.

Yellow crazy ants, proving it is possible to feel sorry for a cockroach.
Bradley Rentz/Wikimedia Commons, CC BY-SA

Beating ants means turning their biology against them. Bait needs to be attractive enough for workers to bring back to the colony and share, but not so deadly that they die before they get there. (And yes, this means if you’re spraying foraging ants in your kitchen you won’t get rid them for good, because the queens are somewhere hidden, laying more eggs and making more ants.)

Most ant eradication programs take three to four years to fine-tune their baiting regime because of a multitude of factors that need to be considered, such as seasonal changes in ant foraging behaviour and food preference, and the desire to avoid harming non-target species. Typically, two to six treatments are required, depending on the ant species, the size of the area, and the habitat type.

Beating the 1%

The hardest part of ant eradication is the end-game. Getting rid of the final 1% requires first finding them. This may mean painstaking searches through hundreds of hectares of bushland and residential areas, and the placement of hundreds of thousands of lures. Detector dogs can be very helpful, but they cannot be used in all environments and also need substantial resources for training, handling, and maintenance.

Ironically, it is at this stage that public and political support for eradication programs is most likely to wane, because ant numbers are too low to be seen as a threat to the public, economy or environment. Yet it is vital not to stop now, or else the remaining 1% will simply build up their numbers again. Experienced staff are also lost when programs suffer cuts or delays in their funding.




Read more:
Eradicating fire ants is still possible, but we have to choose now


Disappointingly not mentioned in the budget was funding for eradicating electric ants. Like red imported fire ants, electric ants have a painful sting, and when left to multiply will eventually turn gardens and swimming pools into no-go zones. They also pose a significant threat to native animals such as the southern cassowary, and can blind animals as large as elephants.

They are currently only found in the Cairns region. The National Electric Ant Eradication Program, funded by federal and state governments, ran from 2006 until 2017 and had likely reduced numbers down to that last 1%. The program has been running on state funding with reduced staff since then, but several new detections in the past three months demonstrate the cost of the gap in funding.

In those inevitable “federal budget winners and losers” lists, invasive ants have found themselves firmly in the losers column for 2019. But it’s worth remembering that most of the world’s roughly 15,000 known ant species provide vital services for the functioning of our ecosystems.

They aerate soil and redistribute its nutrients, protect plants from herbivores, disperse seeds, and repurpose dead organisms. They may even help slow down the spread of those pesky invasive ants that are much less friendly.The Conversation

Lori Lach, Associate Professor, James Cook University

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