Invasive predators are eating the world’s animals to extinction

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 https://flic.kr/p/4M2E7y; Richard Adams flickr CC BY 2.0 https://flic.kr/p/7U19v9; Mark Kilner flickr CC BY-NC-SA 2.0 https://flic.kr/p/4D6LPe; CSIRO CC BY 3.0 http://www.scienceimage.csiro.au/image/1515; T. Doherty; Toby Hudson CC BY-SA 3.0 https://commons.wikimedia.org/wiki/File:BrushtailPossum.jpg; CSIRO CC BY 3.0 http://www.scienceimage.csiro.au/image/10564; J.M.Garg CC BY-SA 3.0 https://commons.wikimedia.org/wiki/File:Herpestes_edwardsii_at_Hyderaba.jpg; Harley Kingston CC BY 2.0 https://flic.kr/p/ceWFr7 (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.

The Conversation

Tim Doherty, Research Fellow, Deakin University; Chris Dickman, Professor in Terrestrial Ecology, University of Sydney; Dale Nimmo, Lecturer in Ecology, Charles Sturt University, and Euan Ritchie, Senior Lecturer in Ecology, Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University

This article was originally published on The Conversation. Read the original article.

Killer cats: The devastating impact of feral cats on Australian biodiversity

I recently published a Hot Topic on feral cats for the Ecological Society of Australia.

Hot Topics are evidence-based syntheses of topical environmental issues and they include a database of studies relating to the topic. You can find the summary text below and access the full synthesis here.

JD_cat_v2
Photo by J Dunlop

 

The domestic cat (Felis catus) was introduced to Australia by Europeans and now inhabits all of mainland Australia, Tasmania and a number of offshore islands. Feral cats are opportunistic, generalist carnivores and their potential impacts include: predation, competition and disease transmission.

The recent Action Plan named feral cats as the number one threat to endangered mammals and Federal Environment Minister, Greg Hunt, has called for the ‘eradicat[ion] of all significant populations of feral cats’ within a decade.

Cats prey on at least 400 native and introduced vertebrates in Australia, including 123 birds, 157 reptiles, 58 marsupials, 27 rodents and 21 frogs. Cats have played a key role in the extinction of at least 20 mammals, and are a current threat to several threatened mammal and bird species. Most evidence for the population-level impacts of feral cats has been gleaned from historical patterns of decline and extinction, or from the failure of reintroduction attempts for threatened mammal species. The small amount of experimental work that has been done confirms that cats can suppress and exterminate small mammal populations.

The impacts of competition and disease transmission are less clear. Overlap in resource use between cats and native predators suggests competition may exist, although this has not been confirmed experimentally. Cats carry the parasite Toxoplasma gondii, which can cause death for many marsupials. High prevalence of Toxoplasma antibodies has been recorded in some marsupial populations, although it is not known how infection might alter their behaviour or susceptibility to predation.

Further research into the non-lethal impacts of cats is necessary, as well as a better understanding of the relationship between cats, other predators and their prey.

Feral cats – introduced killing machines eating their way through Australia’s wildlife

Recently, I was lucky enough to talk about my PhD research on feral cats on Radio National’s Science Show, which is presented by Robyn Williams on Saturdays between 12 and 1pm. I discuss a quantitative review of feral cat diet in Australia that I conducted with a group of colleagues. We found that cats consume 400 vertebrate species in Australia, including 16 globally threatened taxa. You can listen to the radio audio here and read more about the study here.

Australia is home to more than 300 species of land dwelling mammals. 85% are found nowhere else in the world. Since Europeans arrived in Australia, just over 200 years ago, 30 mammals have become extinct. This is the highest rate of mammal extinction anywhere in the world. The main culprit for the decline is predation by the introduced red fox and feral cat. Feral cats have recently been named the biggest threat to Australian native mammals. They are eating their way through our wildlife. Tim Doherty is studying the ecology of feral cats in Charles Darwin Reserve, 450km NE Perth. Dissection of cat faeces and stomach contents reveals they predate on almost anything. Tim hopes to collect information which will be useful to land managers as they attempt to control feral cats and protect native fauna from these introduced killing machines. 

Media round up on feral cats

Over the past week or two there’s been a lot of media and opinion pieces about the impacts and management of feral cats in Australia. A couple of papers have been published too.

I thought I would compile all the various articles here because it’s hard to keep up with everything!

Background Briefing Feral cats rewrite the Australian story

Background Briefing The ethics of the dead cat shot

Andrew Cox for ABC Environment Feral cats: how we can solve this problem

Jim Radford for ABC Environment Feral cats will never be eradicated

John Woinarski for ABC Environment Cats are leading a new wave of extinction

Euan Ritchie for ABC Environment Top dogs: Australian predators can provide 24-7 feral cat control

Gregory Andrews for ABC Environment Calling for community support to beat feral cats

ABC Environment Greg Hunt a ‘hero’ for addressing feral cats: Walmsley

ABC Online Feral cats tear through last wild bilby population in Queensland’s Astrebla Downs National Park

ABC Online Scientists call for Tasmanian devils to be reintroduced as mainland predators to combat feral cats

Me for The Conversation To eradicate feral cats, we need to know how many are out there

ABC Online Sniffer dogs track feral cats in the Kimberley as part of wildlife project

The Guardian Environment Endangered species Australia pledges to halt loss of native mammal species by 2020

Chris Dickman and Tom Newsome in Applied Animal Behaviour Science Individual hunting behaviour and prey specialisation in the house cat Felis catus: Implications for conservation and management

Penny Fisher et al. in Applied Animal Behaviour Science How does cat behaviour influence the development and implementation of monitoring techniques and lethal control methods for feral cats?

Hugh McGregor et al. in PLoS One Landscape Management of Fire and Grazing Regimes Alters the Fine-Scale Habitat Utilisation by Feral Cats

“Elusive parrot not a flight risk”

Copyright: Abby Berryman/DPaW
Copyright: Abby Berryman/DPaW

We asked researchers from ECU’s School of Natural Sciences about some of their favourite Australian wildlife. In this piece PhD student Tim Doherty talks about his choice, the Kyloring or the western ground parrot (Pezoporus flaviventris).

Why would a bird perfectly capable of flying decide to spend most of its life on the ground?

It’s a question you could ask a western ground parrot, however locating one of these critically endangered birds could prove a challenge – it’s estimated there are less than 110 left in the wild.

Read more at ECU news

 

“No parenting award for malleefowl”

Malleefowl in northern Wheatbelt, Western Australia. T Doherty
Malleefowl in northern Wheatbelt, Western Australia. T Doherty

We asked researchers from ECU’s School of Natural Sciences about some of their favourite Australian wildlife. In this piece PhD student Tim Doherty talks about his choice, the Malleefowl (Leipoa ocellata).

If awards were given out for the best parents in the animal kingdom, it’s unlikely the malleefowl (Leipoa ocellata) would make the cut.

Read more at ECU News

Why is one of Australia’s most threatened species not on the Red List?

Copyright: Abby Berryman/DEC https://www.facebook.com/photo.php?fbid=549120408453313&set=pb.283796521652371.-2207520000.1376998014.&type=3&theater
Photo credit: Abby Berryman/DEC https://www.facebook.com/photo.php?fbid=549120408453313&set=pb.283796521652371.-2207520000.1376998014.&type=3&theater

The IUCN Red List is the principal resource for the conservation status of threatened species, yet one of Australia’s most threatened species isn’t on the List, and here’s why: Continue reading