For three years a team of researchers combed newspapers, old books and Parks and Wildlife records in a bid to collect every sighting ever of the Tasmanian tiger. It was a painstaking process but the reward was a chance to track the extinction of the iconic species.
Small collections of sightings had been collated previously but never before had a group of researchers brought together every recorded sighting of the thylacine. Now thanks to scientists from the University of Tasmania a database exists where anybody can view the details behind every sighting since the 1930s.
UTAS professor and Australian Lauriat Fellow Barry Brook said for the first time they were able to scientifically analyse the sightings to examine when the thylacine went extinct.
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There have been no confirmed sightings of Tasmanian tigers since the last captive animal died at Hobart Zoo in 1936 despite there being more than 1200 reported sightings - the most recent of which was made last year.
Professor Brook said it was easier to believe the species went extinct when the last captive animal died because there was no concrete evidence to show the animal still roamed Tasmania's wilderness.
But, through analysis of the more than 1200 sightings, now collated in their database, Professor Brook and his team found the likely extinction date for the thylacine to be in the late 1990s.
The group analysed each sighting and provided extra weight to "expert" sightings - those made by experienced bushmen, wildlife experts or people who had previously come into contact with thylacines.
"Obviously there are different levels of credibility that you can attach to those types of sightings and so part of our analysis was attaching probabilities to these different sightings and accepting or rejecting them probabilistically," Professor Brook said.
"So there was a chance that even a tourist who saw something was right but it is a small chance and there was a large chance that they were wrong. So their sighting was down-weighted in the analysis as a consequence."
After assigning each sighting a probability of being accurate the group ran computer models on the data in a bid to determine the date of extinction. The models they used were widely accepted in the science of extinction biology and have been used to track the extinction of other rare species globally.
"When we did that we were able to determine that the most likely extinction dates are between the late 1990s or early 2000s which is much later than a lot of people might imagine," Professor Brook said.
"But the extinction interval is wide because of the uncertainties and the probabilities. So it could have occurred anywhere from the 1960s through to the small probability that the thylacines still exist in more remote areas of Tasmania even today."
Professor Brook said there was probably less than a one in 10 chance that the thylacine still existed in the remote areas of Tasmania.
"But it is not extraordinarily improbable as some previous work has suggested," he said.
"And that really only came about by taking a truly comprehensive look at all the records. [This work] also points out to people that it is worth making sightings and making reports to authorities, or to researchers, because they can be taken seriously.
"They are never believed or disbelieved they are taken into account."
This work forms part of Professor Brook larger look at the impact of humans on the natural environment. Along with tracking the extinction path of the thylacine the group also developed a new method of mapping the hotspots of sightings The new method could help scientists determine the likelihood of threatened species inhabiting a certain area.
"There are actually many species where we just don't know whether they are extant or extinct. They haven't been seen for either years or decades and they are hard to document," Professor Brook.
"It is very difficult to prove that something is extinct because that is evidence of an absence and all you can really have is the absence of evidence. This is the general problem for threatened species - how do we know that a threatened species is in a particular place?
"It can be important because decision on conservation might rest on whether a certain area has certain protected or threatened species in there. If they are unlikely to because they are already extinct then that will have management implications and vice versa if there is high uncertainty or there is reasonable probability that threatened species exist in an area and it is under consideration for protection or management then this is important information to contribute."
The database of thylacine sightings is publicly available. New sightings can be reported to Professor Brook via email - Barry.Brook@utas.edu.au. All new sightings can added to the database.
"The idea here is that moving forward anyone can pick up this and do whatever they want with it, and add to it, and that will allow more clarity going forward into the future," Professor Brook said.
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