Odds-on it’s gone Torsten Blackwood/AFP/Getty

What are the odds that Tasmanian tigers still exist? About 1 in 1.6 trillion.

Mathematical models provide yet another good reason to think the fabled Australian species is long gone, despite occasional claims of sightings.

The Tasmanian tiger or thylacine (Thylacinus cynocephalus) once occupied most of Australia, but competition with dingoes drove it to extinction on the mainland about 2000 years ago. An isolated population persisted on the island state of Tasmania until it was colonised by the British in the 19th century. Hunters were paid bounties for killing thylacines to protect sheep. The last known individual died in captivity in 1936.


But the idea that a few thylacines might be clinging on in remote wilderness continues to make headlines around the world. The most recent batch of stories came after Bill Laurance at James Cook University in Townsville, Queensland, and his colleagues announced plans to investigate the remote Cape York peninsula at the northern tip of mainland Australia, where there were two claimed sightings in the 1980s.

Both sightings occurred at night – one was reported by a park ranger and the other by a camper. The park ranger spotted a creature resembling a thylacine during a patrol, while the camper stumbled across a pack of four as he walked around his campsite with a torch.

Both descriptions of body size, shape and striped markings are consistent with Tasmanian tigers and do not match any other animals in the area, like dingoes or wild pigs. Since the researchers publicised their upcoming search mission, other people have come forward with tales of recent sightings.

Mistaken identity?

However, mathematical modelling by Colin Carlson at the University of California, Berkeley, and his colleagues suggests the probability of Tasmanian tigers being alive in 2017 is virtually zero.

His team collected data on confirmed and unconfirmed sightings from 1900 onwards to model the likelihood of thylacines being extinct at different points in time. Their least optimistic scenario considered only the confirmed sightings, whereas the most optimistic factored in the unconfirmed sightings, too. The team’s most optimistic estimate predicts that thylacines could have clung on in the wild only until the late 1950s. The probability that they are still alive in 2017 is 1 in 1.6 trillion, the modelling suggests.

One problem with this model is that it is based purely on recorded sightings, and may be less applicable to far-flung wildernesses like Cape York, says Brendan Wintle at the University of Melbourne in Victoria, Australia. His research team has developed an alternative model that includes data about previous searches in remote regions, as well as aspects of the animal’s biology and behaviour such as its nocturnal nature, which makes sighting less likely, and its size. However, even this model concludes that the latest possible extinction date for Tasmanian tigers is 1983. “Unfortunately, we have also drawn the curtain,” says Wintle.

Laurance says he welcomes these modelling studies for “injecting a note of sobriety into the discussion”. “We agree that it’s exceedingly unlikely – we’ve been saying that from the outset,” he says.

But even if the search fails to uncover a scrap of evidence of Tasmanian tigers, it will still be worthwhile, Laurance says. The team is planning to lay camera traps in areas so remote they are only accessible by helicopter, allowing them to gather unprecedented insights into the local wildlife.

Although he is sceptical, Wintle says he hopes that the surveying mission will prove him wrong about the existence of Tasmanian tigers. “Like everybody else, I would be overjoyed.”

Journal references: bioRxiv, DOI: 10.1101/123331; Global Change Biology, DOI: 10.1111/gcb.13421