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Estimating the extinction date of the thylacine accounting for unconfirmed sightings

Colin J. Carlson, Alexander L. Bond, Kevin R. Burgio
doi: https://doi.org/10.1101/123331
Colin J. Carlson
Department of Environmental Science, Policy, and Management, University of California, Berkeley; 130 Mulford Hall, Berkeley, CA 94720, U.S.A.
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Alexander L. Bond
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Kevin R. Burgio
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ABSTRACT

The thylacine (Thylacinus cynocephalus), one of Australia’s most characteristic megafauna, was the largest marsupial carnivore until hunting, and potentially disease, drove them to extinction in 1936. Current knowledge suggests that thylacines became extinct on mainland Australia two millennia prior to their extirpation on Tasmania, but recent “plausible” sightings on the Cape York Peninsula have emerged, leading some to speculate the species may persist, undetected. Here we show that the continued survival of the thylacine is entirely implausible based on most current mathematical theories of extinction. We present a dataset including physical evidence, expert-validated sightings, and unconfirmed sightings leading up to the present day, and use a Bayesian framework that takes all three types of data into account by modelling them as independent processes, to evaluate the likelihood of the thylacine’s persistence. Although the last captive thylacine died in 1936, our model suggests the most likely extinction date would be 1940, or at the latest the 1950s. We validated this result by using other extinction estimator methods, all of which confirmed that the thylacine’s extinction likely fell between 1936 and 1943; even the most optimistic scenario suggests the species did not persist beyond 1956. The search for the thylacine, much like similar efforts to “rediscover” other recently extinct charismatic species, is likely to be fruitless, especially given that persistence on Tasmania would have been no guarantee the species could reappear in regions that had been unoccupied for millennia. The search for the thylacine may become a rallying point for conservation and wildlife biology, and could indirectly help fund and support critical research in understudied areas like Cape York. However, our results suggest that attempts to rediscover the thylacine will likely be unsuccessful.

Footnotes

  • cjcarlson{at}berkeley.edu, ardenna.research{at}gmail.com, kevin.burgio{at}uconn.edu

  • Article Impact Statement: We show the current search for the thylacine in Australia will likely be unsuccessful, and costs associated with the search will only drain conservation’s limited resources.

Copyright 
The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-ND 4.0 International license.
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Posted September 12, 2017.
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Estimating the extinction date of the thylacine accounting for unconfirmed sightings
Colin J. Carlson, Alexander L. Bond, Kevin R. Burgio
bioRxiv 123331; doi: https://doi.org/10.1101/123331
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Estimating the extinction date of the thylacine accounting for unconfirmed sightings
Colin J. Carlson, Alexander L. Bond, Kevin R. Burgio
bioRxiv 123331; doi: https://doi.org/10.1101/123331

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