Invasive predators are eating the world’s animals to extinction – and the worst is close to home

Originally published on The Conversation. By Tim Doherty, Dale Nimmo, Al Glen, Euan Ritchie and Chris Dickman.

Invasive species are a threat to wildlife across the globe – and invasive, predatory mammals are particularly damaging.

Our research, recently published in Proceedings of the National Academy of Sciences, shows that these predators – cats, rats and foxes, but also house mice, possums and many others – have contributed to around 60% of bird, mammal and reptile extinctions. The worst offenders are feral cats, contributing to over 60 extinctions.

So how can we stop these mammals eating away at our threatened wildlife?

Counting the cost

Our study revealed that invasive predators are implicated in 87 bird, 45 mammal and 10 reptile extinctions — 58% of these groups’ contemporary extinctions worldwide.

Invasive predators also threaten 596 species classed as vulnerable, endangered or critically endangered on the International Union for the Conservation of Nature Red List. Combined, the affected species include 400 birds, 189 mammals and 149 reptiles.

Twenty-three of the critically endangered species are classed as “possibly extinct”, so the number of extinctions above is likely to be an underestimate.

Until now, these shocking statistics have been unknown, and the heavy toll of invasive predators on native biodiversity grossly underappreciated. Species extinctions attributed to invasive predators include the Hawaiian rail (Zapornia sandwichensis) and Australia’s lesser bilby (Macrotis leucura).

Australia’s lesser bilby, now extinct.

Who are the worst offenders?

We found that three canids (including the red fox and feral dogs), seven members of the weasel family or mustelids (such as stoats), five rodents, two primates, two mongooses, two marsupials and nine species from other families negatively impact threatened species. Some of these species, such as hedgehogs and brushtail possums, don’t immediately spring to mind as predators, yet they are known to prey on many threatened species.

Feral cats threaten the most species overall (430), including 63 that have become extinct. This equates to one-quarter of all bird, mammal and reptile extinctions – making the feral cat arguably the most damaging invasive species for animal biodiversity worldwide.

Five species of introduced rodent collectively threaten 420 species, including 75 extinctions. While we didn’t separate out the impacts of individual rodent species, previous work shows that black rats (Rattus rattus) threaten the greatest number of species, followed by brown rats (R. norvegicus) and Pacific rats (R. exulans).

The humble house mouse (Mus musculus) is another interesting case. Despite their small size, house mice have been recorded eating live chicks of albatrosses, petrels and shearwaters.

Other predators that threaten large numbers of species are the domestic dog (Canis familiaris), pig (Sus scrofa), small Indian mongoose (Herpestes auropunctatus), red fox (Vulpes vulpes) and stoat (Mustela erminea).

Invasive mammalian predators (clockwise from top left): feral dog, house mouse, stoat, feral pig, feral cat, brushtail possum, black rat, small Indian mongoose and red fox (centre). Clockwise from top-left: Andrey flickr CC BY 2.0; Richard Adams flickr CC BY 2.0; Mark Kilner flickr CC BY-NC-SA 2.0; CSIRO CC BY 3.0; T. Doherty; Toby Hudson CC BY-SA 3.0; CSIRO CC BY 3.0; J.M.Garg CC BY-SA 3.0; Harley Kingston CC BY 2.0 (centre).

Island species most at risk

Species found only on islands (insular endemics) account for 81% of the threatened species at risk from predators.

The isolation of many islands and a lack of natural predators mean that insular species are often naive about new predators and lack appropriate defensive responses. This makes them highly vulnerable to being eaten and in turn suffering rapid population decline or, worse, extinction. The high extinction rates of ground-dwelling birds in Hawaii and New Zealand — both of which lack native mammalian predators — are well-known examples.

Accordingly, the regions where the predators threatened the greatest number of species were all dominated by islands – Central America and the Caribbean, islands of the Pacific, the Madagascar region, New Zealand and Hawaii.

Conversely, the continental regions of North and South America, Europe, Africa and Asia contain comparatively few species threatened by invasive predators. While Australia is a continent, it is also an island, where large numbers of native birds and mammals are threatened by cats and foxes.

Along with feral cats, red foxes have devastated native mammals in Australia. Tom Rayner

Managing menacing mammals

Understanding and mitigating the impact of invasive mammal predators is essential for reducing the rate of global biodiversity loss.

Because most of the threatened species studied here live on islands, managing invasive predators on islands should be a global conservation priority. Invasive predators occur on hundreds of islands and predator control and eradication are costly exercises. Thus, it is important to prioritise island eradications based on feasibility, cost, likelihood of success and potential benefits.

On continents or large islands where eradications are difficult, other approaches are needed. This includes predator-proof fencing, top-predator restoration and conservation, lethal control, and maintenance of habitat structure.

Despite the shocking statistics we have revealed, there remain many unknowns. For example, only around 40% of reptile species have been assessed for the Red List, compared to 99% for birds and mammals. Very little is known about the impact of invasive predators on invertebrate species.

We expect that the number of species affected by invasive predators will climb as more knowledge becomes available.

This article was co-authored by Al Glen from Landcare Research, New Zealand. Landcare Research is a government-funded research organisation that conducts research into a range of conservation issues, including pest management. It did not provide funding for this research

New project: Can Indigenous fire management restore mammal communities?

I’m excited to say that the Hermon Slade Foundation has thrown support behind my research for a second consecutive year. Last year it was for a project examining the long-term recovery of woodland bird communities following southern Australia’s Millennium Drought (2001-2009), building on previous work  in the region that documented shorter-term responses (see here, here, here, and a perspective piece it inspired here).

My first selfie
Professor Rebecca Bird from Penn State taking a Western Desert selfie with a Martu woman engaging in traditional fire management. Photo from  

This time it is to initiate a study on the capacity for traditional Indigenous fire management to restore mammal communities. The project is in collaboration with Rebecca and Doug Bird from the Human Environmental Dynamics Lab at Penn State, USA, and Euan Ritchie from Deakin University. We will work in remote parts of the Western Desert of Western Australia, where Rebecca and Doug have done ground-breaking work (see here, here, here) on the fire regimes maintained by Indigenous communities and their impacts on native species. We will compare areas under active Indigenous fire management with areas where such management has long ceased to reveal the ecological consequences of an active, traditional fire regime. We are extremely grateful to the Hermon Slade Foundation for supporting this work, and I can’t wait for this collaboration to begin later in the year.

New paper: Does the Configuration of Roadside Vegetation Affect Woodland Bird Communities in Rural Landscapes?

A new paper from PhD student Mark Hall. This is actually Mark’s honours work, so it’s great to see it published (far too few honours theses make it to publication). Well done Mark!


In agricultural regions worldwide, linear networks of vegetation such as hedges, fencerows and live fences provide habitat for plant and animal species in heavily modified landscapes. In Australia, networks of remnant native vegetation along roadsides are a distinctive feature of many rural landscapes. Here, we investigated the richness and composition of woodland-dependent bird communities in networks of eucalypt woodland vegetation along roadsides, in an agricultural region in which >80% of native woodland and forest vegetation has been cleared. We stratified sites in a) cross sections and b) linear strips of roadside vegetation, to test the influence on woodland birds of site location and configuration in the linear network (the ‘intersection effect’). We also examined the influence of tree size at the site, the amount of wooded vegetation surrounding the site, and the abundance of an aggressive native species, the noisy miner Manorina melanocephala. Birds were surveyed at 26 pairs of sites (cross section or linear strip) on four occasions. A total of 66 species was recorded, including 35 woodland species. The richness of woodland bird species was influenced by site configuration, with more species present at cross sections, particularly those with larger trees (>30 cm diameter). However, the strongest influence on species richness was the relative abundance of the noisy miner. The richness of woodland birds at sites where noisy miners were abundant was ~20% of that where miners were absent. These results recognise the value of networks of roadside vegetation as habitat for woodland birds in depleted agricultural landscapes; but highlight that this value is not realised for much of this vast vegetation network because of the dominance of the noisy miner. Nevertheless, roadside vegetation is particularly important where the configuration of networks create nodes that facilitate movement. Globally, the protection, conservation and restoration of such linear networks has an important influence on the persistence of biota within human-dominated landscapes.

Revival of landscape-scale research?

Ideas for Sustainability

By Joern Fischer

It’s easy to by cynical about the state of the world, and the state of academia. A recent commentary in Nature suggested that “current trajectories threaten science with drowning in the noise of its own productivity”. Leading journals are full of technocratic formulas for how to fix the world; while the deeper questions underpinning our sustainability crisis remain unaddressed. But every now and then, there’s a glimmer of hope.

I’ve recently been hopeful about a possible revival of landscape-scale research. To me, conservation science went a bit like this: general principles were being established in the 1960; reserves were advocated in the 1970s; reserve planning was perfected in the 80s and 90s; the “matrix” outside protected areas attracted attention in the 1990s, along with a rise in landscape ecology; ecosystem services arose as a new field of enquiry in the 2000s; and protected areas…

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Great Barrier Reef bleaching is just one symptom of ecosystem collapse across Australia

Originally published  on The Conversation

Media reports around the world have brought the mass coral bleaching of Australia’s Great Barrier Reef into people’s offices and homes.

With 93% of individual reefs showing bleaching, the devastation among researchers, celebrities and the public is palpable.

Unfortunately, mass coral bleaching is just one example of a far broader problem. Although it represents a rapid and extensive example of ecosystem degradation, coral bleaching is not surprising: it is consistent with many changes that are occurring now across Australia’s natural environments.

Coral bleaching has been seen on 93% of the reefs that make up the Great Barrier Reef. (C) XL Caitlin Seaview Survey

The degradation and death of forests

Forest dieback is increasingly common across Australia from the high country and the floodplains to the savannahs.

Our iconic trees – including the world’s tallest flowering plant, the Mountain Ash, and the most widely distributed eucalypt, the River Red Gum – are among the hardest hit.

A stark example is the floodplain forests of the Murray-Darling Basin. Reduced rainfall and water extraction for human needs have deprived River Red Gums of the flooding integral to their existence. The consequence is that 79% of forests on the Murray River have dieback. Tree graveyards are a common sight.

Recent extreme weather combined with recurring wildfire and intensified logging has increased mortality rates of large, old Mountain Ash trees by an order of magnitude. This has created a crisis for the animals that depend on them, including the critically endangered Leadbeater’s Possum.

The collapse of Mountain Ash forests threatens Leadbeater’s Possum with extinction. Greens MPs/Flickr, CC BY-NC-ND

The plight of these forests foreshadows the fate of others (such as Western Australia’s Jarrah forests) under a drying climate.

The decline of south-eastern Australia’s frogs

Australia’s record-breaking Millennium Drought hit frog communities very hard. They have not recovered since.

It was hoped that the heavy rainfalls from late 2010 to early 2012 (the “Big Wet”) would help the frogs “bounce back”, given their capacity to lay large numbers of eggs under suitable conditions.

Modest improvements at the time of the Big Wet were undone with a return to dry conditions. These pushed the frogs back to the dire levels seen during the peak of the drought.

Species whose calls will be familiar to many Australians — the “crick-crick” of the common froglet, the “plonk-bonk” of the pobblebonk — saw very little post-drought recovery.

Frogs such as this ‘pobblebonk’ (or eastern banjo frog) haven’t recovered after the drought. Doug Beckers/Flickr, CC BY-SA

Long dry periods are expected in the region under climate-change models, so the prospects for southeastern Australia’s amphibians seem bleak.

The unravelling of Australia’s mammals

Australia has a remarkably distinctive mammal fauna. However, 30 mammal species have become extinct in the past 200 years. That’s an extinction rate worse than any other country.

Particularly disconcerting is that losses are continuing at an unabated rate, with two Australian mammals lost forever in the past decade.

In much of Australia, particularly in northern Australia, many native mammals that were abundant 20 years ago have become vanishingly rare.

The collapse of bird communities

The Millennium Drought also pushed bird communities of southern Australia over the edge.

On the back of historic declines (primarily due to land clearing), two-thirds of species declined substantially as the drought took hold. The assumption, or perhaps hope, was that these declines were part of a natural cycle, and that the drought’s end would bring a return to normal. This did not happen.

At last count, half of the species — including iconic species like galahs, rosellas and fairy wrens — were still far less common than they were before the drought.

There aren’t as many galahs as there were before the Millennium Drought. Galah image from

The result is that our bird communities have dramatically changed in as little as two decades. As we enter another period of drying, there is grave concern about the future of southern Australia’s birds.

What do Australians value?

These are just a few examples of massive ecosystem degradation. Sadly, there are many more. The battle for Australia’s biodiversity can still be won, but this requires decisive action on climate change and serious investment over many election cycles.

In 2013, Australia ranked among the 40 most underfunded countries for biodiversity conservation, a list otherwise dominated by developing countries.

The budget allocation for the federal Department of the Environment is shrinking and is now less than 0.5% of the government’s spending. It is hard not to draw comparisons with the recent announcement that Australia will spend A$50 billion on submarines.

By contrast, avoiding extinctions of Australian birds would cost around A$10 million per year — a cost we are, at the moment, unwilling to meet.

US Vice President Joe Biden famously said:

“Don’t tell me what you value; show me your budget, and I’ll tell you what you value.”

On May 3, Australia’s government will present its 2016 budget and, with an election looming, we will also soon learn about the opposition’s spending commitments. The coming months will expose how major parties value Australia’s environment, and the election to follow will measure the degree to which Australians accept it.

Bird communities in a land of droughts and flooding rains: riparian tree cover as climate refugia

This post, co-authored with Angie Haslem and Andrew Bennett, originally appeared on The Applied Ecologist’s blog

Something alarming happened in the woodlands of southern Australia last decade. The birds stopped calling. Well, not entirely, but substantially. The chorus of kookaburras, honeyeaters and babblers that usually make the woodland air burst with song was reduced to a whisper.

And we think we know why. The region was gripped by a record-breaking drought, known now as the ‘Millennium Drought’, which spanned nearly a decade from 2001–2009. The drought crippled the region’s biodiversity: frog populations crashed, and over half of terrestrial bird species declined.

Kookaburra (left) and grey crowned babbler (right). Photos courtesy of Rohan Clarke (
Kookaburra (left) and grey crowned babbler (right). Photos courtesy of Rohan Clarke (

When the drought broke spectacularly in 2010 with flooding rains, there was a sense of cautious optimism that the region’s biodiversity might have been offered a reprieve. However, two years after the drought had broken, that optimism turned again to alarm. Monitoring data revealed that although around one quarter of bird species increased following the floods, most species had not recovered. Further still, 14–29% of species (depending on the dataset) continued to decline, despite the drought ending. Promisingly, in our recent paper in Journal of Applied Ecology, we think we have found a hint of a silver lining.

If you read the climate change literature, you may be familiar with the idea of ‘climate refugia’. This concept suggests that some areas are buffered from the impacts of climate change or climatic extremes such as drought. For instance, areas that have relatively high moisture or stable microclimates may offer refuge for species during drought. It follows that these areas should be targeted for protection for conservation, to enhance the capacity of biodiversity to persist during climate change.

The concept provides a sense of agency among conservationists in the face of a looming global disturbance over which we have little control. However, although there is evidence of refugia operating over evolutionary time scales and at continental spatial scales, the evidence that we can create refugia at the scale of conservation management is much scarcer.

Our paper provides that evidence. We found that landscapes with more tree cover on productive soils – such as on riverbanks, stream sides, drainage lines and floodplains, collectively termed ‘riparian vegetation’ – retained a higher proportion of their bird species during the drought.

A typical riparian strip in the study region.
A typical riparian strip in the study region.

This means that past land clearing, for agriculture and other human land uses, is likely to have diminished the capacity of bird communities to resist the impacts of drought. This might explain why the drought had such huge effects on the region’s bird fauna. On the other hand, by protecting riparian vegetation, and by revegetating cleared riversides, floodplains and drainage lines, we could enhance the capacity of bird communities to persist during the next big drought. That is, we could build climate refuges.

Although this sounds promising, our results come with an important caveat. When the drought broke, landscapes with less riparian tree cover tended to ‘bounce back’ to a greater extent. That is they were more ‘resilient’. This is largely because these same landscapes had a greater need for recovery, having lost a greater proportion of their species pool during the drought. By contrast, landscapes with more riparian tree cover lost fewer species and so had less of a need for recovery post-drought. Over the duration of the entire drought–flood cycle, these two opposing trends cancelled each other out such that two years after the drought, a similar fraction of the bird community was lost across all landscapes.

What does this mean? In simple terms, riparian vegetation enhances the ability of landscapes to retain bird species during the drought, but does not arrest longer-term declines that may cause ongoing species loss over successive drought events.

This does not diminish the important role of riparian vegetation for bird conservation during drought. Retaining a larger portion of the species pool throughout the landscape means that ecological functions continue, functions critical to ecological and economic systems, such as pollination and insect control.

Cleared (left) and vegetated (right) riparian strips in the study region.
Cleared (left) and vegetated (right) riparian strips in the study region.

We also know from previous work in these same landscapes that increasing tree cover of any kind increases the richness of woodland birds. Indeed, the total amount of tree cover in the landscape is the most important influence on the number of woodland bird species that can occur. Adding riparian tree cover to heavily modified landscapes gives huge ‘bang for your buck’ in terms of bird conservation, as productive areas support more species and provide specialised habitat for species that favour riparian vegetation. Finally, other work has revealed that landscapes with more tree cover had more stable bird communities, measured in terms of species turnover, over the duration of the drought.

Combined, these results suggest that maintaining and revegetating riparian areas will provide many benefits to bird conservation. It also has many other benefits, including protecting water quality, enhancing aquatic environments, and creating a visually attractive environment. It’s a ‘win-win’ for sustainable land management and nature conservation.