Abstract
Like the Dodo and Passenger Pigeon before it, the predatory marsupial Thylacine (Thylacinus cynocephalus), or ‘Tasmanian tiger’, has become an iconic symbol of human-caused extinction. The last captive animal died in 1936, but even today reports of the Thylacine’s possible ongoing survival in remote regions of Tasmania are newsworthy and capture the public’s imagination. Extirpated from mainland Australia in the mid-Holocene, the large island of Tasmania became the species’ final stronghold. Following European settlement in the 1800s, the Thylacine was heavily persecuted and pushed to the margins of its range, although many sightings were reported thereafter—even well beyond the 1930s. To gain a new depth of insight into the extinction of the Thylacine, we assembled an exhaustive database of 1,237 observational records from Tasmania (from 1910 onwards), quantified their uncertainty, and charted the patterns these revealed. We also developed a new method to visualize the species’ 20th-century spatio-temporal dynamics, to map potential post-bounty refugia and pinpoint the most-likely location of the final persisting subpopulation. A direct reading of the high-quality records (confirmed kills and captures, in combination with sightings by past Thylacine hunters and trappers, wildlife professionals and experienced bushmen) implies a most-likely extinction date within four decades following the last capture (i.e., 1940s to 1970s). However, uncertainty modelling of the entire sighting record, where each observation is assigned a probability and the whole dataset is then subject to a sensitivity analysis, suggests that extinction might have been as recent as the late 1980s to early 2000s, with a small chance of persistence in the remote south-western wilderness areas. Beyond the intrinsically fascinating problem of reconstructing the final fate of the Thylacine, the new spatio-temporal mapping of extirpation developed herein would also be useful for conservation prioritization and search efforts for other rare taxa of uncertain status.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
B.W.B., S.R.S., C.R.C. and J.C.B. conceived the project and developed the database, B.W.B. analyzed the data and wrote the paper, B.W.B., I.J. and J.C.B. created the display items. All authors discussed the structure, results, and interpretation, and commented on the manuscript.
Authors declare no competing interests. The data supporting the results will be archived in an approved public repository with a data DOI. The code is hosted at github.com/bwbrook
The main results remain unaltered. However, the paper has been thoroughly revised, with many sections expanded and/or re-written in parts, with the whole paper restructured to suit a more traditional format. Furthermore, additional scenarios have been included to more widely explore the full range of possible interpretations of the data. A new Table 1, based on physical records only, has been included (the old Table 1 is now Table 2).