Authorities are considering introducing Tasmanian devils onto Wilson's Prom to decrease the feral cat population. But biologist Allen Greer says there's little evidence the devils will make any difference.
The Victorian government is considering releasing Tasmanian devils onto Wilson’s Promontory to reduce the number of cats and foxes and their impact on native species. Planning is well advanced, and a decision is due soon. The project may lead to other introductions of devils onto the mainland.
None of the media accounts of this plan, however, has mentioned a current study that might give some understanding as to the impact of introduced devils on a long-established cat population. This study takes advantage of the recent introduction of devils onto Maria Island, off the east coast of Tasmania, where cats have been established for over 100 years. The study will monitor any effects the devils may have on the cats and, provided the pre-release studies were robust, should provide insight into the likely impact of introduced devils on an established cat population.
Tasmanian wildlife authorities are also clearing two Tasmanian peninsulas of devils in order to restock the fenced peninsulas with healthy devils, creating two sanctuaries of devils free from devil facial tumour disease. Presumably, the authorities have foreseen the potential of these two “natural experiments” for assessing the devil’s impact on cats and are monitoring the resident cat populations as the devils are removed and will monitor them again as devils are returned.
But although these studies should be informative, existing information suggests devils might have little effect on cats.
Devils are generally heavier and have more powerful jaws than cats. In a physical encounter between similar-sized animals, the devil would probably prevail. Cats, however, are more agile and quicker than devils, and they climb better. Hence, a healthy cat could easily avoid direct contact with a devil. As one devil expert put it, a devil would be able to kill a cat only under “very advantageous conditions”.
There is direct evidence that cats avoid devils. In this video an adult cat feeding on a carcass suddenly looks over its shoulder and then bounds off, just before a slightly larger devil moves into the frame.
Spotlighting surveys show that in some areas where the number of devils observed has decreased due to devil facial tumour disease, the number of cats observed has increased. However, the data is variable, and the number of cats observed was already climbing before the devil population began to decrease.
It is also unclear, however, whether the increased number of cat sightings is due to an increase in the actual number of cats or to a loss of fear in cats. Some anecdotal evidence suggests it may be the latter. If so, the benefit to native wildlife remains undetermined.
It is also thought devils might compete seriously with cats for food and rearing dens, and eat their kittens.
As to competition for food, devils and cats are both active about the same time of night, and both live by a combination of hunting and scavenging. Devils, however, probably get more of their food through scavenging while cats get more through hunting. Devil stomachs and scats usually contain the remains of animals too large to have been caught and killed, whereas cats’ usually contain the remains of smaller animals.
It seems unlikely, therefore, that devils would compete significantly with cats for food.
As to competition for rearing dens, female devils and female cats both use a den in which to give birth and rear their young until weaning, but devils, being heavier and bulkier than cats, are unlikely to be able to fit into most cat dens.
As to predation, adult devils would probably have to dig their way into a cat den to eat the kittens, and there is no evidence of this to date.
Overall, it seems unlikely that devils will have much impact on cats. Rather than rush to introduce devils to Wilson’s Prom and other mainland sites, it would be best to wait for the outcome of the current study of devils and cats on Maria Island and the two experiments involving the depopulation and repopulation of peninsulas on mainland Tasmania.
Allen Greer is a biologist who writes about science and nature. His on-going summary of the Tasmanian Devil, its biology, facial tumour disease and conservation can be found here.
Dec 18, 2013
Data appears to show populations of Tasmanian devils have stabilised. Biologist Allen Greer asks why you're not hearing that from the state government or advocates of "saving" the devil.
If you’ve heard about the Tasmanian devil, you probably know that a transmissible tumour, devil facial tumour disease (DFTD), threatens the species with extinction. But you probably don’t know that for the last five years the devil population in the wild has stabilised, albeit at levels about 80 to 85% lower than pre-disease times.
The reason you wouldn’t know this is the data is in a graph in a Tasmanian government report, and the result has not been mentioned in any of the government’s public information sites. It is most notably absent from the Save the Tasmanian Devil Program’s website, which describes itself as “your primary source of authoritative, up to date information on Devil Facial Tumour Disease. We will keep you informed of what is being done to save the Tasmanian Devil and how you can help.”
The graph is a plot of the number of devils sighted in the state government’s annual state-wide spotlighting surveys along 172-odd 10-kilometre road sections between 1985 and 2012. Spotlight Summary Report 2012-13 reveals a decline in devils beginning with the appearance of DFTD in 1996 and then a levelling off beginning in 2008 and continuing to the present …
Raw counts of additional mammal species observed during the Annual Statewide Spotlight Surveys, mainland Tasmania (2002-2012)
This survey and the data it gathers represent the longest and geographically broadest continual monitoring of the devil population available. The data is robust and used routinely in other research articles on the devil.
That something is up is also suggested by a single passing comment in the media. A 2013 New Year’s Day newspaper report said in some areas the devil population had “unexpectedly stabilised”. This information could have only come from within the STDP. The apparent stabilisation also now explains why, since early 2010, official statements of the decline in overall devil numbers have remained unchanged at 80-85%.
The STDP maintains at least three “long-term monitoring sites” that might or might not be informative as to the status of the devil populations. The names and locations of the sites are not in the public domain, so it is not clear if they are new sites, in which case they would be relatively uninformative, or old sites for which population estimates were available up until 2007 or 2008, depending on the site, but then stopped. Toward the end, surveys at these old sites were providing the first indications the populations might be stabilising. In fact, the populations at some of the old sites, such as those on Forestier/Tasman and Freycinet peninsulas, are slated for removal and replacement, thus eliminating their value in providing insight into the long-term progression of DFTD.
Despite the recently published spotlight survey results indicating a stabilising of the population as a whole, the STDP wrote on its website as recently as September 2013: “There is no evidence to date of the decline in devils stopping …”
Why have the Tasmanian government, the STDP and devil researchers all been silent on this potentially important development in the progress of the disease? One can only speculate. But the fact that the entire STDP is based on a story of an inexorable decline in the devil population, any news the decline may have stopped could jeopardise the STDP’s funding base. This is especially the case with funding from private donations, solicited nationally through the Save the Tasmanian Devil Appeal and the STDP website, and internationally through the recent initiative of sending “ambassador” devils to overseas zoos.
If the devil can save itself, what need is there for the Save the Devil industry?
*Dr Greer has a PhD in biology, and was formerly a principal research scientist at the Australian Museum. He is unaffiliated with any institution.
Dec 19, 2012
The campaign is well underway to protect the Tarkine's natural and cultural heritage after approval was given this week for the Shree Minerals iron ore mine in western Tasmania. The ANU's Andrew Macintosh writes on the politics and policy.
Federal Environment Minister Tony Burke yesterday gave the go-ahead to the Shree Minerals iron ore mine in the north-west of the Tarkine in Tasmania. It’s one of eight major projects scheduled for the region, and signals the start of what is sure to be a lively period in the campaign to protect the Tarkine’s natural and cultural heritage.
Not surprisingly, conservationists have expressed outrage at Burke’s decision. This reaction is partially related to the threat that the mine poses to the iconic and endangered Tasmanian devil. The north-west of the Tarkine is home to one of the few remaining populations of disease-free devils. The Shree Mine is located in the heart of this area and the road along which the ore will be transported has been identified as a devil hot spot.
Several conditions have been imposed on the mine in an attempt to minimise the threat posed by ore-loaded B-doubles and other mine vehicles. These include running regular instruction sessions for workers on the importance of the species and how to minimise the risk of road kill; erecting posters and distributing glovebox guides on the same; preparing a plan on how to protect the species from the impacts of the mine and road traffic; running a free bus service to shuttle workers and others to and from the site; “taking all reasonable measures” to ensure vehicles do not exceed 50km/h when travelling to and from the site; and removing carcasses from the road every day.
Shree Minerals is also required to donate $350,000 to the Save the Tasmanian Devil Program Appeal over seven years. Further, in the event that more than two devils are killed in any 12-month period at the mine site or by authorised vehicles travelling to or from the mine, Shree Minerals is required to pay an additional $48,000 to the appeal. How the Department of Environment came up with the $48,000 figure is a topic worthy of investigation. Based on current population estimates, it suggests the species is worth roughly $1.7 billion.
There are similar conditions for the other two threatened species that are likely to be affected by the mine and its vehicles: the spot-tailed quoll (a small carnivorous mammal) and the Tasmanian wedge-tailed eagle.
While the attempt to reduce animal mortality is laudable, the scepticism expressed by conservationists towards the conditions is understandable. For starters, Shree Minerals has no legal authority over vehicles owned by other parties travelling to and from the mine site. And does anybody really think that handing out glovebox guides and running information sessions is going to significantly reduce mine-related animal mortality?
Whatever management measures are put in place, the establishment of the mine will increase the risk to the population, both from roadkill and through the potential introduction of the disease to the area. Given the perilous state of all three species, particularly the devil, it is difficult to reconcile Burke’s decision with the statutory requirement that “the conservation of biological diversity and ecological integrity … be a fundamental condition in decision-making”.
Beyond the threat posed by the mine to the threatened species, Burke’s decision has clarified how the Gillard government intends to deal with the Tarkine heritage nomination and the remaining projects. Some conservationists believed that, if it was going to intervene on any project in the region, it would be the Shree Minerals mine because of its diminutive size and the threat it poses to the devil and quoll.
The approval has made it clear that Burke intends to approve all of the major proposed projects and draw the boundaries of the Tarkine National Heritage Area around the project sites.
The Tarkine National Heritage area will end up covering only those parts of the region that are already included in reserves or for which there are no known significant commercial uses.
The entire Tarkine saga, from its origins in the 1960s through to now, has been a drawn-out case study in the difficulties associated with heritage conservation and the interplay between the Australian and state governments. It demonstrates the urgent need for an overhaul of the federal environmental and heritage laws and the re-establishment of an independent national heritage body that can ensure areas of world and national heritage significance receive appropriate protection.
*Andrew Macintosh is an associate professor at the ANU College of Law and associate director of the ANU Centre for Climate Law & Policy
Gavin R. Putland, of Prosper Australia, writes: Tony Abbott is quite right: the carbon price “amounts to a reverse tariff” in that it taxes the carbon intensity of Australian products but not imported products.
I’ve been complaining about reverse tariffs for more than four years. Welcome aboard, Mr Abbott! What Abbott didn’t say is that the carbon tax, which will raise about $8 billion a year, will be only the fourth-biggest reverse tariff in Australia’s tax system.
The third-biggest, which raised about $18 billion in 2010-11, is payroll tax, which taxes the labour content of Australian products but not imported products. This discriminatory quality strengthens the claim that payroll tax, in so far as it applies to labour embodied in goods, is an unconstitutional duty of excise.
The second-biggest, which raised something like $54 billion in 2010-11, is the payroll tax masquerading as the superannuation guarantee. A federally mandated, employer-funded 9% super contribution is equivalent to a federally funded 9% contribution paid for by a 9% federal payroll tax. Doubling the GST, though I don’t recommend it, would be a far more sensible way to pay for super, because the GST is “border-adjusted” (taxing imports while sparing exports) but otherwise affects prices in much the same way as a payroll tax.
State payroll taxes and the federal super guarantee are patently worse than the carbon tax, not only because they raise more revenue, but also because they tax something desirable (jobs) rather than something undesirable (pollution).
But the biggest, baddest reverse tariff, which raised about $200 billion in 2010-11, is income tax in all its forms. Australia’s income tax penalises income earned in production of Australian products but spares income earned in production of imported products.
In other words, it amounts to a value-added tax without border-adjustment. If it were called a “VAT” or “GST” without border-adjustment, it would not pass the laugh test in any developed country. But separate the value added by labour (wages) from the value added by capital (profit), tax them separately, shoot them full of loopholes, rebrand the whole sordid mess as “income tax”, and you get the mainstay of the tax system in almost every developed country. It’s one of the great con jobs of the past 100 years.
Hence, I am pleased that the carbon price will at least raise the personal income-tax threshold, allowing employers to offer useful amounts of part-time work without having to withhold personal income tax (or any part of the low-income tax offset).
I confess that I will be more pleased if the carbon price is converted to a simple tax before it creates any private property rights. We discourage smoking and drinking by taxing tobacco and liquor, and I fail to see why pollution should be treated any differently. We didn’t create tradable rights to smoke or drink, and I fail to see why we should create tradable rights to pollute.
But those who are concerned about reverse tariffs should have bigger fish to fry.
Kevin Bonham writes: Re. “Minister’s Tarkine decision a threat to Tassie devil” (yesterday, item 14). In their article on mining proposals in the Tarkine as a supposed threat to Tasmanian devils, Deb Wilkinson and Andrew Macintosh refer to “the fact that the Tarkine is the last remaining stronghold of disease-free devils.” Actually, no matter how many times that mantra is repeated, it isn’t fact.
First, large areas of western Tasmania outside the Tarkine — and not just wilderness areas that are seldom visited — are currently free of any known records of Devil facial tumour-diseased devils. While this does not prove there are no diseased devils in such areas, it is even more doubtful whether devils in the Tarkine are in fact all disease-free. For instance, in February a CODE Green video purportedly showing a diseased devil “near a proposed mine site in the Tarkine” was released by Senator Milne.
Surely if a movement has been using the area’s disease-free status as an argument for its protection, and evidence appears that that argument is possibly false, then it is time for that movement to admit that the case for protecting the area based on the devil is weakened.
Not so for Senator Milne, who was happy to switch from arguing that the absence of disease justified protecting the area to arguing that the presence of disease justified protecting the area. And indeed, such instrumental uses of the Tasmanian devil as a trump card to attempt to achieve political goals, completely irrespective of the facts, have been rife ever since it was listed as threatened.