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An Invasive Plant Is Killing Wombats in Australia

The views expressed are those of the author and are not necessarily those of Scientific American.

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When an otherwise nocturnal wombat shows up in the daylight, acting lethargic and having trouble walking, you know that animal is in trouble.

When thousands of wombats turn up sick, emaciated, balding and dying, you know you have a crisis.

That’s what’s happening in Murraylands, South Australia, where up to 85 percent of the region’s southern hairy-nosed wombats (Lasiorhinus latifrons) are sick or dying, apparently the victims of invasive plants that have taken over the local ecosystem.

Brigitte Stevens, founding director of Wombat Awareness Organization, was one of the first to observe the sick wombats three years ago. At first glance the animals appeared to be suffering from a balding disease such as sarcoptic mange, which has previously been observed in wombats. But the problem got worse each year and by this May Stevens had documented more than 2,800 dead or dying wombats. “Some of them just lying down on their sides, just eating dirt, [and] can’t even lift their heads,” she told the Australian Broadcasting Corp. She thinks many more wombats may be sick or dead in their underground burrows where they can’t be counted.

Necropsies performed on several of the wombats by wildlife veterinarian Wayne Boardman and veterinary pathologist Lucy Woolford, both lecturers at the University of Adelaide, ruled out mange. Instead, the animals were found to be suffering from a liver disease, most likely caused by an innocuous-sounding plant called potato weed (aka common heliotrope or caterpillar weed, Heliotropium europaeum). Potato weed, which was introduced to southern Australia in the 19th century and has since spread across most of the continent, contains pyrrolizidine alkaloids (PAs), chemicals that protect them from insects but which can be fatal or dangerous to many animals, including livestock such as pigs, cattle and horses.

At least three other invasive plants were found in abundance in the region, none of which are palatable to wildlife, but potato weed is the only one containing the dangerous PAs. The native Mitchell grass (several species of the genus Astrebla) and spear grass (Heteropogon contortus) that historically formed the bulk of the wombat’s diet appear to have been squeezed out of the region.

The preponderance of invasive plants and lack of edible vegetation has a twofold effect on the wombats, Boardman says. Some of the animals are malnourished, which is partially responsible for their fur loss (alopecia). “Some die and some will undoubtedly get better—given more nourishing food,” he says.

But those who ingest the potato weed are much worse off. “Potato weed leads to hepatic necrosis [liver death],” Boardman says. This in turns leads to the production of chemicals that make the skin more sensitive to ultraviolet light. The animals then suffer severe sunburns, which lead to vasculitis as well as necrosis of the skin.

Research into the effect of potato weed and other invasive flora on the wombats is ongoing. Writing for the Australian site The Conversation, Boardman and Woolford suggest that it could be possible to “remediate” the wombats’ habitat by killing off the invasive weeds and replanting native vegetation, but further study is also necessary to find out why the plants took over that region in the first place.

Southern hairy-nosed wombats are not currently an endangered species, but with up to 85 percent of the Murraylands’s wombats affected by this liver disease, that’s an assessment that may not last much longer.

Photo 1: A healthy southern hairy-nosed wombat by James Reed via Flickr, used under Creative Commons license. Photo 2: A dying wombat, courtesy of Wombat Awareness Organization. Photo 3: Potato weed in Spain by Ferran Turmo Gort via Flickr, used under Creative Commons license

John R. Platt About the Author: Twice a week, John Platt shines a light on endangered species from all over the globe, exploring not just why they are dying out but also what's being done to rescue them from oblivion. Follow on Twitter @johnrplatt.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Carlyle 6:25 pm 07/13/2012

    More information on this weed.
    Research funding for real problems like this are sadly lacking while millions are being wasted on things like windmills. It could turn out that the problem is not caused by this weed. It is not new to the area but with only a couple of researchers dedicated to investigating the problem, they face a daunting task.

    Link to this
  2. 2. yalla 10:44 am 07/16/2012

    Well this is a surprise, to see my home turf featured at this site.
    I live in the Murraylands and have been heavily involved in environmental stuff here for a couple of decades. That includes hand rearing a SHN wombat [mother was road kill]and revegetating the property on which we live.
    And I have mixed reactions to the article above.
    I don’t want to knock it because the motivation of the people involved is good but there is a little more to the situation than reflected in the article.
    Its complex.
    I’m doubtful about the impact of the weed as the major cause of the problem – and there is a problem with wombat numbers – because its been going on for several years not just the last few and a few other considerations I won’t go into.
    We, a group of wombat carers and local landowners, became very concerned about the scarcity of wombats several years ago. At least 5 years ago I think from memory. Various reasons for the dramatic decline, 80% was the estimated mortality with particular impact on mature females, were mooted, mange being the major suggestion. I was not convinced, nor were several of my associates. For starters researchers [including vets] who looked at, and captured and released, wombats on my property found no mange and in fact the wombats at my place were in excellent health and condition whilst death was everywhere around them.
    We tried to get a political response.
    I was active in local and state politics at the time and had contact with several relevant govt and academic depts. But to no avail, the response was complete indifference. One article in a local newspaper and nothing else. Bloody depressing.
    I don’t think potato weed is the villain. I’m not sure of course. I’m not a scientist but I’ve had scientists at this place constantly for yonks, been knee deep in them.
    Valuable people.
    I suspect mange is part of the problem, or at least was some years back.
    But the real reason, in my opinion, is pretty darn simple and alluded to in the article.
    Habitat destruction.
    Wombats are tough critters but the land around here is severely degraded. Most of it. Extremely degraded.
    The land was cleared almost entirely of its native vegetation decades ago and then cereal cropping attempted. When that failed because the soils are poor and rainfall erratic and marginal for cropping [the regional average, pre climate change, was around 300 mm pa but variable] pastoralism took over and when that failed the agricultural viability of the land away from river irrigation became close to nil. The ecosystem here has been stripped. There are some 30-40 weed species that infest the region. Even after nearly 20 years of revegetation our property still has [some] weeds and is still nowhere near what it was 200 years ago. But its better than what is around it and so our wombats [and other critters and plants] are thriving by comparison.
    What is needed is massive re-generation of the land around here.
    Unless that happens we are pissing into the wind.
    Despite lots of lovely words from some politicans, local and state, nobody is really interested. Well nobody with sufficient political clout.
    As I have been typing this I have become progressively more frustrated and depressed. You know that old joke [?] about the fella walking along the beach throwing back into the water critters stranded by a storm and his mate says “Why? You can’t possibly save them all!” And he responds, as he picks one up and puts it back into the safety of the water “No, but I can save this one”.
    Well thats how I/we [there are more here than just me] feel. We tried, got nowhere on the large scale so we just keep making our place[s], like I said there’s a few involved in the region, better by getting rid of weeds by physically removing them and outgrowing them with local natives.
    Anyway I suppose its a positive that the spotlight has turned onto the plight of the wombats to some extent now so thats good.
    But I’m still pretty much in despair.
    Oh, last thing. Its not just wombats who are having problems. The whole biodiversity thing is affected.

    Link to this
  3. 3. John R. Platt in reply to John R. Platt 1:47 pm 07/16/2012

    Thanks so much for your comment, Yalla. I understand your frustration and despair. It seems like so much of conservation is a constant, uphill battle. Sisyphus always comes to mind, painfully.

    Keep fighting the good fight and doing good for the creatures and ecology around you.

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  4. 4. jonathanseer 4:42 pm 07/16/2012

    Just another example of why Australia is the absolute worst nation when it comes to wild life preservation. I really don’t care what the reason is. The proof is ample that Australia as a nation is guilty of wholesale destruction of their fauna and flora the likes of which the world has never been seen before.

    With 1.3 Billion people China still finds room for Pandas.

    With 1.2 Billion people India still is home to the tigers and only 1/2 the land area of the island continent.

    Australia which barely has 20 million people and much less than that for most of its history exterminated it’s marsupial Tiger in the 1930s and has NOT learned anything from that.

    Instead they adopt the same pokey, slow motion response that allows members of their unique fauna to simply go extinct while they figure out the problem.

    The problem is Australia knows what the problem is, but they as a nation simply do not care.

    Too bad as a nation they cannot have the national conscious that the Chinese and Indians do about wildlife.

    The sad irony is Indians and Chinese get slammed for being responsible for modern pressures on wildlife, but it is Australia, and Australia alone that accounts for the overwhelming majority of animals on the RED LIST.

    It’s time to call them on their grotesque negligence, and stop giving them credit for doing everything possible, when the results show they are doing just enough to make the rest of the world think they care.

    They care alright about the millions of sheep that have so degraded the land native wild life can barely sustain themselves.

    What is so utterly pathetic about that is there are so many much more profitable and less intensive ways to use the land than raising high impact sheep, but old ways die hard, and Australians seem to think the world can’t live without their average quality wool.

    It’s time they move on from some of the most destructive animal husbandry practices the world has ever seen, and even get creative and develop new ones that utilize the native fauna.

    Link to this
  5. 5. yalla 6:30 pm 07/16/2012

    My post above was the result of late night blog reading. Its now morning, I’ve returned from walking the dogs and a cold frosty walk it was at that.
    That’s what this problem of declining wombat numbers is all about.
    Here, try this for a relevant footnote. Its an excerpt from the foreword to “A Field Guide to the Mammals of Australia” Pub. 2001 and it , the foreword, is written by Mike Archer Director of the Australian Museum, Prof of Biological Sciences Uni of NSW.
    ” With 65% of the continent now under the thumb of unsustainable agriculture focused on introduced species and land degradation costing an estimated $5 billion annually accumulating every year the future for most Australian mammals is in doubt……
    We [Australians] live in the shadow of a growing mountain of scientific literature documenting so many long and short term declines that the brightest view in sight is a distinctly backwards one. But what worries me even more than the decline or losses of particular species is the failure to focus on conserving the capacity of evolution to replace these extinctions….
    What are required to turn current trends around are trials of new….conservation strategies. In addition to such valuable traditional strategies as protected areas and conservation we must be prepared, like many other countries around the world, also to trial sustainable harvesting of wildlife, programmes of species reintroduction ….even native animals as pets…..strategies based on above all valuing our precious wildlife and rediscovering sustainable ways to put people and natural environments back together for the benefit of both.
    Without values driven conservation strategies I fear the struggle for the survival of both will be lost before the end of this century.”

    Unfortunately the prof is an optimist, most Australians, or perhaps more accurately particularly those in positions of power, do not value our environment. Quite the opposite, it is still seen essentially and mainly as a source of profit.

    Anyway thanks for the forum,to the other contributors and thanks for the series you are writing.
    Important stuff.

    Link to this

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