The Lost World? A Third of Planet’s ‘Extinct’ Mammals are Alive

Tasmanian-Tiger_2 Last week Conservation International reported that its scientists had rediscovered three species of amphibians, including a Mexican salamander not seen since 1941. Australian species returned from the supposed dead also include Gilbert's pottoroo and Leadbeater's possum, Victoria's state animal emblem that was found in 1961 after not being seen for half a century. The Tasmanian Tiger, left, was believed hunted to extinction by settlers on the Australian island state of Tasmania during the 19th century. The last known thylacine died at Hobart Zoo in 1936. Could they still exist?

Many animals feared extinct have actually been found alive and well, adapting to different habitats. "I think it might be useful to know that rediscoveries are not random," says Diana Fisher of the University of Queensland, who led the work. "If we know which types of species are most likely to be alive but hard to detect we might be able to better target searches for missing species."

Globally, the number of animals declared extinct continues to increases significantly. However, about one third of mammals that have been reported as possibly extinct at some stage have been rediscovered. 

Diana and colleague Simon Blomberg analysed the circumstances surrounding mammal rediscoveries around the world. They found that animals affected by loss of their habitat were much more likely to be mistakenly classed as extinct than those affected by hunting, disease or introduction of predators. 

"Many species feared extinct from habitat loss have in fact turned up in a different habitat, because they were more flexible than we realised," says Diana. "Some species can also persist in marginal habitat for some time." 

For example, the Malabar civet (Viverra civettina), from India, suffered an almost complete loss of its coastal riverine forest habitat. It was last seen in 1929 and thought to be extinct, before being rediscovered in 1987 in a cashew plantation. 

"This study will help conservation agencies to prioritise limited resources towards searching for species with some chance of being rediscovered, rather than vain searches for species certain to be extinct, like the thylacine," says Marcel Cardillo, a conservation biologist at James Cook University in Queensland. The montane monkey-faced bat in the Solomon Islands would be a good contender, says Diana.

The finding probably won't significantly boost rediscoveries in Australia, where more mammals have gone extinct than anywhere else, however. "No Australian mammals have been driven to extinction primarily by habitat loss," says John Woinarski, director of biodiversity for the Northern Territory. 

One of the most amazing rediscovery story is of the Guadalupe fur seal (Arctocephalus townsendi), says Diana. The seal was hunted to apparent extinction off Mexico in 1892, but in 1926 a tiny colony was found by two fishermen. One went to a biologist at San Diego Zoo, offering to sell him some. The fisherman went back and caught two males for the zoo, but then argued over the amount of money he should be paid. 

"He said he was going to go back to the spot and slaughter them all out of spite – and apparently he did," says Diana. He turned up in Panama with skins to sell, but was killed in a bar-room brawl before he could reveal the colony's location. 

Then in 1950, another zoologist at San Diego Zoo heard about the story and tracked down the second fisherman on his deathbed. "The fisherman must have felt guilty because the day before he died, he described where the seals had been," says Diana. "Researchers from the zoo went to San Nicholas Island, off southern California, and succeeded in finding a small colony alive in a cave."  Today the main population on Guadalupe Island numbers 12,000-15,000.

Casey Kazan via australiangeographic.com.au

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