Australasian Science: Australia's authority on science since 1938

Bounty Was Sole Cause of Thylacine Extinction

By Stephen Luntz

Human factors alone were enough to wipe out the Tasmanian tiger, modelling suggests.

Around 2000 thylacines were killed for the government bounty placed on them, but questions have been asked as to whether this was enough to explain their extinction. The dramatic drop in the number of bounties paid after 1905 and the discovery that thylacines lacked genetic diversity (AS, July/August 2012, p.9) has been taken as evidence that disease may have been a major contributor.

However, Dr Thomas Prowse of Adelaide University’s School of Earth and Environmental Sciences says: “We tested this claim by developing a ‘metamodel’ – a network of linked species models – that evaluated whether the combined impacts of Europeans could have exterminated the thylacine, without any disease”.

Once the loss of tiger habitat and the replacement of wallabies with sheep were factored in, Prowse found there was no need to invoke disease. “We showed that the negative impacts of European settlement were powerful enough that, even without any disease epidemic, the species couldn’t escape extinction,” Prowse says.

Evidence for disease is sketchy, with one report of diseased animals from a single area, and while Prowse says “it was from the right time, it wasn’t written down until 50 years later”.

The justification for the bounty lay in reports of thylacines attacking sheep, but Prowse says the evidence is that this was rare and largely “a beat-up”. In fact, “there were few accounts of tigers even being in the area when sheep were taken”.

Prowse adds that attacks by feral dogs may also have contributed to the thylacine’s extinction, but this is not required by the modelling. “The thylacine would probably still be around today if not for the bounty scheme,” Prowse says, “but habitat loss may have been responsible for the loss of 50% of their numbers”.