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Thylacine; the Improbable Tiger

By Guest Author Nick Mooney inZoology |
Score: 11.4 / 65.2

The dog-headed pouched one

The thylacine Thylacinus cynocephalus was a large, heavily built, carnivorous marsupial with short, dense, tan coloured fur and incomplete, dark brown bands across the back, rump and base of the tail. The scientific name translates as the "dog-headed pouched one" and like canids (dogs), the thylacine was a digitigrade quadruped . Superficially the teeth, head, neck and forequarters appeared very canine-like making one old, parochial name, the "pouched wolf" perhaps more appropriate than the usual "Tasmanian tiger", although the latter is a clear winner in both imagery and marketing. There were however, obvious differences with the placental canids, aside from the marsupial pouch.

The thylacine tibia  was relatively long and the tarsus  short with pads extended up the tarsus to the ankle, unlike the haired tarsi of canids. Also with padded tarsi, the thylacine's relatives, the Tasmanian devil Sarcophilus harrisii and quolls Dasyurus spp., use the structures for extra grip while climbing, much as does a human or bear but there is no evidence thylacines did likewise. Toes of thylacines were relatively small with large plantar pads, the feet having plantar:single digit pad area ratios of about 9:1, compared with 4:1 with most canids. Claws were not retractile. When walking the thylacine had a languid motion with a distinctive gait (pattern of footprints) but when running at moderate speed was said to have a somewhat disjointed, stiff motion, indeed once reported as a "shambling canter". Although not especially fast, the species was reportedly dogged in pursuit of prey, mainly using scent. Ears were rather bear like, of moderate size as were the eyes, with no particular adaptations for nocturnal habits. Thylacines could jump such as might a heavy dog and swim but could not climb.

The thylacine brain case was relatively small compared with canids, perhaps because it did not have their sophisticated social organisation. Thylacine had more teeth than canids and in common with the large dasyurids (Tasmanians devils and quolls) the carnassials  were barely distinguishable from other molars whereas those of canids, felids (cats) and mustelids (weasels) are typically massive and prominent. The canine teeth of thylacine were somewhat rounded in cross section compared to those of canids which have a sharp trailing edge, better adapted for ripping. The thylacine skull was long and narrow, more so than that of a wolf Canis lupus, suggesting no specialisation for massive prey (a low aspect ratio giving more power) and indeed prey of the thylacine was mostly other marsupials smaller than itself (e.g. wallabies). The changing shape of thylacinid skulls over the eons shows clear evidence of evolutionary convergence towards large canids specialising in pursuit; evidence perhaps of the thylacine’s evolutionary trajectory. Despite not being relatively powerful the thylacine’s long narrow jaw was still very large, absolutely strong and could reportedly deliver a precise bite (the thylacine searcher David Fleay showed the author the famous scar on his derrière from such a bite received in the Hobart zoo). Thylacines did occasionally kill large hunting dogs in self-defence. Thylacines were entirely carnivorous and wild individuals were reportedly reluctant to scavenge, although there is a report of one feeding on the carcass of a stranded whale and they occasionally got caught in traps baited with meat.

Thylacines were substantial predators with the largest males reaching 36 kg (78 lb), about 20% more than adult females. Head and body length was up to 130 cm and the long drooping tail with its very long vertebrae up to 65 cm; some thylacines were nearly 2 m long. The wedge-tailed eagle Aquila audax and the thylacine were Tasmania’s top predators (both species competing with Tasmania’s Aboriginal people to some degree), much larger than the meso-predator (and efficient scavenger) the Tasmanian devil (7-12 kg). In body proportions (a good indicator of preferred habitats) the thylacine was very similar to the puma Felis concolor of the New World, a species famous for its use of a wide range of habitats although both species prefer diverse, dry, open forests containing various refuges.​

An adult ​thylacine photographed at the Hobart Zoo in 1933 (Image credit: Public Domain; National Archives of Australia).

Few thylacine vocalisations were reported and unfortunately none recorded, the most commonly heard being a nasal, terrier-like doubly yip, reportedly used within hunting pairs.

The species was usually found as individuals or pairs, at the most in family groups. This essentially solitary nature is probably why Tasmanian Aboriginal people apparently made no domestic use of the species, as distinct from dogs which were quickly utilised as pets and hunting companions as soon as brought to Tasmania by Europeans.

Breeding was, at most, annual and a maximum of 4 young could be reared per litter (there being only 4 nipples in the rearward facing pouch). Gestation has been estimated at about 35 days with pouch life of about 140 days. A period of denning (usually in caves) would then apply for perhaps about 5 months, and the young were apparently dependent on the parents until near full-grown, a common phenomenon in sophisticated predators. Thylacines never bred in captivity, hence the dearth of precise knowledge of breeding cycles, nor was its ecology and behaviour formally studied, more the pity. It was rare for thylacines to live longer than 9 years in captivity (12 was the rare maximum). In those days of (generally) crude husbandry, captive devils rarely lived for more than 5 years whereas wild devils free of Devil Facial Tumour Disease can get to 7 years old with a generation time of 3 years. Thus it is reasonable to suggest wild thylacines might live to 13 years, probably with a generation time of 5-6 years.

The species was originally widespread across New Guinea and mainland Australia, those in Tasmania becoming isolated when Bass Strait last formed 8,000-10,000 years ago, saving them from dingos (the Australian wild dog) which by then had not spread that far south. Extinction on mainland Australia occurred 1,000-2,000 years ago; it is thought mainly from predation by and competition with Aboriginal people and dingos.

The tragedy unfolds

Once the English introduced sheep into Tasmania’s prime thylacine habitat conflict was immediate, unleashing European "predator hysteria". Thylacines did kill sheep, but losses were often wildly exaggerated. Private bounties were offered and eventually (and notoriously) in 1887 the Colonial Government introduced a bounty intended to exterminate the thylacine. Based on the usual relationship between trophic level, mass and home range size, we can predict the thylacine’s usual home range size at 20-50 km2. Thus, Tasmania likely held a maximum of about 2,000 adult thylacines when Europeans arrived, an estimate supported by the collapse of the population through the bounty period between 1888 and 1912. No bounties were claimed for the last 3 years of the scheme but the 2,184 thylacines recorded represent on average 104 killed animals/yr, well above sustained yield, which from body mass, fecundity and life span we can estimate at about 10% per year of the total population. Indeed, that calculation suggests that by the beginning of the bounty there may have only been 1,000 thylacines left. Once the bounty ceased few were caught and then mostly for museums and zoos. The last authenticated thylacine was trapped in 1933 and died miserably in captivity in 1936 on 7th September, a date that now has become Tasmania’s Threatened Species Day. Ironically, the species was protected just two months before, on 10th July.

Shooting thylacines was not the main problem. Thylacines were shy animals and were mostly snared, in particular during the bounty period (Image credit: Public Domain; original photograph is at the Tasmanian Museum and Art Gallery).

There are anecdotal claims that disease played a part in the downfall of this species. Perhaps a combination of relentless hunting, habitat loss, disease and competition with and predation by feral dogs was the cause of functional if not biological extinction. At least inbreeding did not seem to be a severe problem – thylacines appeared to breed normally right to the end. There may have also been "own goals", too. Perhaps, like its distant relative, the Spotted-tailed Quoll D. maculatus, thylacines may have had female philopatry, a system in which young males disperse to find non-related females while young females stay near home making (re)colonising areas very hard. Moreover, with some species there seem to be social thresholds of minimum numbers below which the population quickly collapses (e.g. passenger pigeon Ectopistes migratorius). Perhaps this too applied to the thylacine.

Even after thylacines ceased to be hunted, a baggage train of anthropogenic influences continued. In the Great Depression of the 1930s people competed with them for wallabies, routinely poisoning carnivores that might ruin pelts of snared wallabies. Later when, at best, thylacines were exceedingly rare, rabbits built to plague numbers and vast amounts of strychnine was laid in response, much of it in potential thylacine habitat. The next accidental assault came via the change from strychnine to 1080  for herbivores control. Although unlikely to kill thylacines since there is an evolutionary exposure and considerable consequent tolerance by Australian marsupial carnivores to the toxin, 1080 provided devils with abundant carcasses and their numbers steadily increased. What was originally likely only occasional predation on thylacine pups by a devil population held in check by thylacines could then in my opinion become overwhelming. All in all a sadly familiar drum-roll of serial local extinction.

To me, two issues are outstanding; firstly, whether the species is indeed biologically extinct and secondly, why are some people so fascinated with that question?

Considering the vast amounts of land where hunting did not occur, the assumption that humans caught the last thylacine in 1933 is outrageous hubris. Based on likely densities in those relatively untouched areas I think there were perhaps 100 left. The key, though, is how many were in contact during that part of their life when they can breed and I have suggested elsewhere that perhaps 50 were in that category. But what has happened with these animals in the 15 or so thylacine generations since (a period representing about three human generations) - by any measure a very long time to have an absence without extinction or authentication. Refreshingly however, the classic dilemma now manifests itself in that, in general, anecdotal evidence almost invariably precedes (re)discovery by more formal means (remember the coelacanth!) and also follows the inability of those formal means to any longer authenticate a species. This makes a lack of authentication simply that and does not necessarily represent extinction, although for practical reasons we have adopted an arbitrary period of 50 years absence from authentication as representing extinction .

The era of sightings begins

Since 1936 there have been many hundreds of claims of thylacines seen, footprints found and vocalisations heard. Dead ones have even been reported (trapped, shot, road-killed and found), sometimes glibly (such as poachers reporting illegally trapping and releasing one in 1972), but almost invariably so long after the fact that confirmation has not been possible. There have also been a variety of hoaxes including photographs but nothing has yet passed muster as irrefutable evidence. The issue has increasingly become clouded with myth, the invention by some enthusiasts of the concept of "sub-proof", politicisation (e.g. attempts to use the species to prevent logging) and last but not least, conspiracy theories, for which Tasmanians are justly famous. Indeed, when employed as a government wildlife biologist I was accused of hiding the existence of the thylacine to protect the forestry industry (in reality the thylacine’s continued existence would probably be used by government to vindicate development!).

Intriguingly, "good" reports of thylacine come from all across mainland Tasmania (clearly not reflecting reality) and, dubiously, from parts of mainland Australia and even New Guinea. This gives the obvious problem in that if one accepts a report as "good" then one must equally accept other comparable reports wherever they are. Law courts have long recognised that on their own, sighting reports are fundamentally problematic as evidence. The report may be correct (i.e. it was a thylacine), a mistake (e.g. mistaken identity), an illusion or a lie, options that can be hard to whittle down. Where detail (distance, lighting, time, physical description) is such that a mistake is highly unlikely then almost invariably the issue comes down to the credibility of the witness(s). Familiarity with local animals can actually be a problem through anticipation and secondary elaboration so any accurate observer can be credible. But to me there are basically two practical categories. The first from witnesses I know well and trust and not inclined to exaggerate and the second from witnesses with no apparent vested interest, even to the point it would seem against their interest to make the report (forestry or mine workers might be placed in that category) and apparently not inclined to exaggerate, as determined by interview and event reconstruction.

No definitive photos have been managed, perhaps not surprisingly because by my reconstructions people routinely exaggerate times by up to 400%. This makes the usual reported sighting time of less than 10 seconds more like 2-3 seconds, simply not long enough to get a photo. On many occasions people have left their cars to look unsuccessfully for signs of the animal. I have often done the same with common animals crossing the road to test the method, almost without exception finding no evidence.

There are many more reports than published because most are given in confidence and the most "famous" are not necessarily the most credible. The best with which I am familiar include one in 1973 near Ben Nevis (north eastern Tasmania) by perhaps the State’s best naturalist and his companion while driving a truck slowly down a bush track. Two thylacines reportedly ran in the headlights for 50 m just in front of the vehicle. Another outstanding report was in 1988 with 7 people in 2 cars, the first car reportedly passing a large thylacine on the side of the road in daylight then stopping some 30 m past, the animal then crossing the road behind in full view of the car’s occupants and those of the following car 40 m away and approaching. At the moment I am in possession of a copy of a plaster footprint (see attached photo) reportedly cast in situ in 2010 by a highly respected bushman and naturalist. It is certainly of a thylacine but in reality I do not know if it is authentic or a skilful hoax.

On the right-hand side a plaster cast of what I think is the hind foot of a medium-sized thylacine compared to a very large devil (about 11 kg) casts (left-hand side; hind at the top, partial fore at the bottom). The cast was reportedly made in 2010 in Tasmania but that cannot be proven (Image credit: Nick Mooney).


The famous sighting in 1982

I have been involved as a participant or advisor in many searches, most notably one following the famous 1982 report of a sighting at close quarters south of Togari by the wildlife officer (and my colleague) Hans Naarding, something made public after we finished the search. The event can be paraphrased as

"It was March 1982 and I was surveying Japanese Snipe amongst wetlands in far northwest Tasmania. In the late evening I had gone to sleep in the back of my vehicle parked at a road junction in remote forest 30 km south of Togari. At 2 am I awoke and out of habit scanned the vicinity with a spotlight. As I swept the beam around to my amazement it came to rest on a large thylacine standing in full view on gravel almost side on just 6-7 m away. With stretched arm, contorted around the door pillar, I held the light on it, counting stripes and otherwise absorbing the scene. It was raining but the visibility was very clear; I even noted how dry it looked and that it was a male. After about 2 minutes of careful observation I thought to get my camera bag but to do so I had to take the light off it and by the time I retrieved the bag and relocated the animal it was disappearing into adjacent dense scrub. Camera in hand I got out of the vehicle, more or less ‘the full Monty’, but the animal had gone. I noticed a strong smell, very reminiscent of a brown hyena (I had been a game guide in East Africa). I then searched the gravelled vicinity, doing so again first thing in the morning before going to find a phone to report the event to my boss but could find no sign of the animal."

Well, it was hard to dismiss the unambiguous report of one of Tasmania’s most experienced and respected wildlife officers and senior management (indeed all staff) thought it "worth a go". An immediate response was mounted by the famous thylacine researcher Eric Guiler (University of Tasmania) and David Rounsvell (Parks and Wildlife Service). Carcase drags and predator calls were used together with spotlighting, night watches and automatic cameras developed for a recent thylacine project run by Stephen Smith and funded by the then World Wildlife Fund. After several weeks the intense (and potentially disturbing) activity was ceased, but the cameras were left in situ. I was then asked to undertake monitoring of the area to try and confirm the presence of thylacine.

I had to decide how I could maximise chances of detection. Automatic cameras were then clumsy, unreliable and had high serviceability. Nobody knew what a thylacine scat looked like (and devil scats are both large and incredibly variable), so an option was searching the many hundreds of carnivore scats in the area to see if any contained thylacine hairs swallowed during grooming. DNA testing of possible scats was then impractical, although we did unsuccessfully try to develop a bile salt test. I did some careful research of thylacine specimens to make sure I had the best reference material for footprints etc., even turning up a windfall of photos of wet preserved feet, distinct from shrivelled feet of mounted specimens. But the dense vegetation and plethora of old logging roads gave an advantage. It is well known that carnivores will often follow habitat edges, and this extends to the use of modest vehicular tracks, the trend being stronger with dense forest. Tasmanian devils certainly demonstrate this – in dense forest their footprints invariably go along, not across, tracks. I think tracks give efficiency of movement and may concentrate prey to a certain extent. Tracks and roads break the canopy, providing light for regrowth and grasses – basic food for herbivores. As the forest opens up this relationship between predator presence and tracks breaks down, probably because diffuse light scatters the food opportunities and movement is easier. Upon frame-by-frame development of the famous silent, b/w movie of a captive thylacine I could describe the unique walking gait. By my calculation, thylacines walking would leave about 4.5 prints per metre. Using comparable dogs on beaches, I estimated that a running thylacine would leave about 1.2 prints per metre. Assuming they covered a bit more distance than devils – say, 12 km per day – and assuming half was walked and half run, they should leave 4.5 x 6 x 1,000 + 1.2 x 6 x 1,000 = 27,000 + 7,200 = 34,200 footfalls per night; a huge potential resource.

Well, that proved to be wishful thinking. The true resource is of course how many of these footfalls turn out to leave footprints that might be recognised and it quickly became clear that the chances of getting a clear, very rare thylacine footprint even in ideal substrate (damp mud/sand) were miniscule considering chance and the hyper-activity of local devils unless I could separate them. So, I came up with systems of obstacles intended to filter devils. I used logs that devils would most likely go around, as they are very poor jumpers, which the larger thylacine should easily cross, in doing so getting recorded by camera, hair brush or sand pad. Another filter was two sand pads within 10-20 metres of each other. The first one a devil encountered would get much attention – sniffing, snorting, defecation, urination and sometimes a uro-genital drag. That in turn would focus the next devil and the next. The result was that one of the pair of print traps would usually get trashed while the other was simply transited, leaving fewer, clearer prints. A further devil filter was a wallaby or wombat carcase 5-10 m off the track to try and tie up local devils at least for one night.

Importantly I had to decide on how big an area to search and I asked Bob Harden, familiar with how dingos used such habitats, for advice. Any thylacine Hans saw might be anywhere in its home range. Following accepted relationships of principles of predator size and area they need and tapping into Eric Guiler’s intimate knowledge of diaries kept by shepherds while hunting particular thylacines, I estimated an adult thylacine’s home range to be about 8 km in diameter. To cover all possibilities of where in its home range "Hans’ animal" may have been, I therefore needed to search a minimum area about 16 km in diameter, about 200 km2. In the end I included what I thought to be ideal adjacent areas ending up monitoring about 250 km2, checking 89 existing and 256 artificial sand/mud pits every 3-4 days, in the end spending the better part of 15 months in the area. Despite a few heart stopping moments with partial footprints and fleeting glimpses of animals in dim light, I did not confirm Hans’ report. My boldest conclusion was that there were probably no resident thylacines there while I searched. I could have been wrong – who knows what they do without neighbours – maybe their home ranges would be vastly greater and places visited more rarely.

Doing it again I would use many digital trail cameras and DNA analysis of scats but retain the best of sand pads and mud patches to cover the fallibilities of high-tech gear. I would also pick a place without many observers (meaning thylacines may have been missed) but clearly suitable, partly judging that on the relative abundance of wedge-tailed eagles, a competitor preferring similar habitats.

Time will tell

Private searches continue unabated, from traditional reactions to reports through very sophisticated use of "Buckeye" technology linking multiple trail cameras with wi-fi, sending real time photos to a base. Importantly there are also now many "accidental searches" involving hundreds of trail cameras doing various wildlife surveys. I’m more than curious to see what this surge in use of new equipment of an effectiveness we used to only dream about, will bring. Let’s hope any evidence of thylacine is treated with thought, care and respect for what would be surely the mother of all survivors. Although we seem to have left the days of cavalier attempts to catch thylacine (thanks to modern cameras) there remain a hard core of enthusiasts that consider capture is still necessary. I dread to think of the shenanigans of the inevitable circus and ask them is that really just to feed their own egos.

I don’t agree with the hypothesis that thylacines can’t be found because they have become uber-cryptic. I think it’s more about our inability to grasp that once species are under particular detection thresholds they are simply very hard to find without great persistence, intelligent and responsible techniques, and a huge slice of luck.

The enthusiastic criticism (some better described as venom) directed at the recent precautionary response to reports and pieces of hard evidence of red foxes Vulpes vulpes in Tasmania does not bode well for any change to the presumed extinction of thylacines based on sighting reports, something many enthusiasts want. The insistence by sceptics that the fox response should have only been based on repeatable, systematically collected data I think has lifted the bar that high (through fear of criticism and ridicule) that with the next incursion this species, so predictably destructive in Tasmania, will probably become well established before a response is mounted; dangerous stuff.

However, the consequences for the thylacine of such a false negative may not be severe in that it is hard to imagine what we can do to help the species beyond what is actually happening. Tasmanian devils, a competitor and probable predator of thylacine pups has greatly diminished and eagles are still suppressed. No hunting of thylacines occurs and nearly 50% of Tasmania is in reserves. In developed areas, including wilderness fringes, wallabies and possums are in unprecedented numbers and there remain many refuges for secure breeding. With the demise of devils illegal poisoning of this species and also of eagles (to protect stock), using farm chemicals undoubtedly deadly to thylacines, has greatly decreased and feral dogs are very rare compared to what they were in the thylacine’s halcyon days. In addition urbanisation is rife – less people live in the bush. So, aside from greatly increased road traffic I regard the Tasmanian landscape as good for the thylacine.​

View from Cradle Mountain over suitable thylacine habitat (Image credit: Public Domain, Pixabay)

Despite the obviously long odds, I for one am still open minded about the possible existence of the species. Even allowing that "absence of evidence is not evidence of absence", the hard evidence is very poor. But just when the issue seems settled I get reminded of the claims of those few people I know well who tell their ordinary, credible stories of close encounters. Science is an endless matrix of greys defying the modern, impatient demand for black and white. The longer I indulge in natural history the more I am reminded of our ability to overlook things, even large things. Devil Facial Tumour Disease, a very obvious malady in a large, very common icon, was completely missed until it was over perhaps 1/3 of Tasmania. So, yes, despite the obvious odds, we maybe missed a few thylacines. I hope so.


Further reading on this topic:

  • Archer M. (Editor, 1982). Carnivorous Marsupials Vol 2, Royal Zoo. Soc. NSW.
  • Guiler E., R., (1986). Thylacine: The tragedy of the Tasmanian Tiger. Oxford Univ. Press.
  • Guiler E., R., (1993). The Tasmanian Tiger in Pictures. St David’s Park Pub.
  • Guiler E., R. and P. Godard (1998). Tasmanian Tiger; a lesson to be learned. Abrolhos Pub., Perth.
  • Lang R. (Editor, 2014). The Tasmanian Tiger; Extinct or Extant. Strange Nation Publishing
  • Moeller H. (1997). Der Beutelwolf. Westarp Wissenschaften, Magdeburg.
  • Owen D. (2003). Thylacine; the Tragic Tale of the Tasmanian Tiger. Allen and Unwin.
  • Owen D. and D. Pemberton (2005). Tasmanian Devil; a Unique and Threatened Animal. Allen and Unwin.
  • Paddle R. (2000). The Last Tasmanian Tiger; the History and Extinction of the Thylacine. Cambridge Univ. Press.
  • Smith S., J. (1981). The Tasmanian Tiger – 1980. Parks and Wildlife Service, Tech. Rep. 81/1, Hobart Tasmania.



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Responses

Michael O'Connor

Excellent article with some details that I have not seen before. There are just so many reports that i think they have to be out there.

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Helena

It's so thrilling to read about this mysterious animal - hopefully it's still out there! And hopefully it'll be rediscovered. This really would be an enrichment for all of us.

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