Saturday, September 9, 2017

Thylacine: Specimen Or It Didn't Happen

This week a group of Tasmanians (press conference hereclaimed to have seen and to have footage of a living thylacine, a species which has not been confirmed to exist since the last known specimen died in captivity on September 7, 1936.    No zoologist has yet accepted this extremely blurry footage as being of a thylacine, and many wildlife observers consider it is very likely to be a spotted-tailed quoll.

You can see a longer video here.  It contains unconvincing (compare actual accounts) "barking", the video above, something unidentifable nosing the camera, and a bunch of Where's Wally pics in which you can just make out what might be the eyes of something if you try very hard.  When I slow down the main video frame by frame I can see blurry paler patches on the animal consistent with the spotting on a spotted-tailed quoll.  The most interesting thing about the videos is actually the large number of lyrebirds (introduced to Tasmania) that they show.

I thought it might be of some interest to someone out there to outline my position regarding this poor animal the thylacine, and the intermittent circus of alleged "sightings", "photos" and "videos" surrounding it.  As usual, I am expressing my own view and not necessarily the view of any organisation I belong to or any employer I from time to time work for.

My position regarding the thylacine derives from a chat with a now-deceased scientific colleague in the 1990s.  He worked in a museum and now and then was presented with media enquiries surrounding this beast.  He said that he was not interested in sightings, photos or footprints of claimed thylacines as it was too easy to fake them.  The claim that the thylacine was still out there in the Tasmanian bush several decades since its alleged extinction was so extraordinary that the only adequate evidence for it, in his view, was an actual thylacine specimen.

In the time since, animation, robotics and related aspects of film technology have hardly stood still and my late colleague's standard for proof has only become more valid.  The Booth Richardson Tiger Team video is a genuine video of an animal that there is no convincing reason to believe to be a thylacine, but even if someone produced a video apparently showing a real thylacine, the least unlikely explanation would be a hoax.

It has been surprising to see some expert comments assigning a real probability (around a third or a fifth) of the depicted beast being a thylacine.  It's possible these quotes do not present what was said in its full context.  It might be that such probability assessments would be fair enough if one assumed that thylacines still existed in reasonable numbers.  But given the lack of any hard evidence that they still exist at all, I don't agree with these estimates.

Indeed, that a poor-quality video does not say anything about the chance that the animal still exists is not just something that should be obvious, but is also a view with strong mathematical support. Anyone can plug this into Bayes' Theorem for themselves, using:

* their prior estimate of the chance of thylacines still existing
* their estimate of the probability of a poor quality video (of something that looks like it might be a thylacine but could be various other things) emerging if one assumes that thylacines do still exist
* their estimate of the probability of such a poor quality video emerging if one assumes that thylacines do not exist.

Both of the latter probabilities are very close to 1 (ie 100%) over a sufficient time frame, which means that a video like this shouldn't shift one's evidence of the chance of thylacines existing much at all. Even if one believes they do, a given animal of this appearance in a video is still not likely to be one given that the alternatives are all much more common.

This is so because there is a high level of video filming of animals going on (especially through camera traps that are increasingly affordable and common, and also because of the increasing prevalence of mobile phones and cheap cameras with video capacity).  Clearly the "team" in this case did a large amount of work of this sort.  Not all animals will be clearly recognisable in video footage and there are plenty of things out there that, in blurry form from a distance, are not reliably distinct from thylacines.  Since these sorts of videos are highly likely to occur from time to time whether thylacines occur or not, they don't tell us anything about whether or not they do.

It is easy to look at the vast expanses of the south-western Tasmanian wilderness and imagine that thylacines could still roam there without being noticed by anyone.  However the historical evidence is that this was not generally an animal of the deep south-western rainforests but rather preferred the woodlands and grasslands that in the 19th and early 20th centuries were the most cleared, farmed, degraded, inhabited and hunted parts of the state.   Given that the animal was never very common at the time of European "settlement" and then was deliberately persecuted and moreover affected by a disease at a time when its numbers were already low, the chance it is still out there is not good.  My estimate of the chance this animal still exists in Tasmania: a generous 2%.  If I'm wrong and it is proven to be out there, I'll give myself an Ehrlich Award.

But Species Are Rediscovered All The Time ...

Yeah, tell me about it.  Please do, I want to hear more.  Oh, can I have bad-quality video with that?  While there is indeed a major problem with scientists routinely writing off species as extinct when there is not nearly enough evidence for their extinction, the thylacine is in general at the wrong end of the spectrum.  Rediscoveries most often happen when the missing species is small, very cryptic, poorly searched-for, little-known, widespread and assumed to have become extinct only because of habitat loss or for no known reason at all.  The thylacine has been one of the most searched-for suspected extinctions of all time.

Thylacines And Foxes

The question of proof beyond doubt is delicate in Tasmania because of the state's recent controversy regarding the alleged presence of foxes.  There is an argument that goes: hey, we haven't been able to catch a live fox in Tasmania though we know they are here, maybe the same is true of thylacines.  But really in the case of foxes, we never knew it in the first place.  Following video footage of a fox running off a boat in Burnie, foxes were claimed to be present in the state on the basis of physical evidence including various carcasses, DNA-tested blood and numerous DNA-confirmed scats, as well as large numbers of "sightings".  But it could never be proved that the carcasses were not imported, or that the scats were not either imported or else contaminated or misdiagnosed during the testing process, while sightings (especially poor ones) were correlated with media coverage.  So the matter remained inconclusive.

Maybe one day we will get a claim of continued thylacine existence that is based on DNA evidence taken from a claimed scat or claimed hairs, for example.  Even in that case, the fox example suggests we should be cautious.

Thylacine Believer Infighting!

The overconfidence of the latest band of thylacine believers in their video of what appeared to be a quoll was amusing enough, but the whole thing descended into farce when a rival group  attacked the evidence and dished out some of its own.  "Hey I see your large quoll passed off as a thylacine and raise you an obvious feral cat!" The group also had the rump of an animal with a few stripes on its back (no indicator of scale, plenty of other striped animals out there) and a few other images that could be anything (foxes and wallabies the most obvious suspects).

A Boon For Conservation?

There is a certain romantic appeal in the notion of an already rare animal, having been persecuted to the brink of extinction, somehow surviving undetected only to be found again by some everyday Joe or Flo decades later after all the scientists had failed.  But those who would see such a thing, if it happened, as a great day for conservation are in sore need of a reality check.  It would actually be a disaster.  For starters, it would make one of the biggest problems in Tasmanian conservation (the comparative overspending on a very small number of flagship species that sometimes aren't all that threatened) even worse, but worse still it would be a big problem for the credibility of warnings about extinction.  Any claim that even the most shameless and permanent habitat destruction posed the slightest threat of wiping out a species would be met with sniggers about scientists who said things were going extinct: "You said the thylacine was gone and now you expect us to believe we're going to wipe out some worm you can barely even find anyway?  As if!"  The over-hyping of extinction threat claims is a serious problem for conservation anyway - having thylacines running around would be more of a reality check than it could handle.

Extraordinary claims demand extraordinary evidence.  No more of this sad parade of sightings, unconvincing videos and other tall stories re thylacines.  For all claimants the standard should be the same: produce an actual thylacine, or else go home.

(Legal warning: A permit is required to capture or possess a thylacine, living or dead.)

1 comment:

  1. I found it interesting that they had all this close-up footage of all sorts of animals going about their business, oblivious to the cameras filming them, but the thylacines apparently conduct all their business hiding behind the bushes where they can't be seen. Especially interesting was the fact that this carnivore appeared not to be interested in eating any of the prey animals they share a habitat with ...