A population of endangered giant tortoises, which once dwindled to just over a dozen, has recovered on the Galapagos island of Española.
The finding is described as “a true story of success and hope in conservation” by the lead author of a study published in the journal PLOS ONE.
About 40 years after the first captive-bred tortoises were reintroduced to the island, the Española giant tortoises are reproducing and restoring some of the ecological damage caused by feral goats brought to the island in the late 19th century.
The global population was down to just 15 tortoises by the 1960s.
Now there are 1,000 tortoises breeding on their own.
“The population is secure,” says James P. Gibbs, a professor of vertebrate conservation biology at the SUNY College of Environmental Science and Forestry.
“It’s a rare example of how biologists and managers can collaborate to recover a species from the brink of extinction.”
Gibbs and his collaborators used 40 years of data from tortoises marked and recaptured repeatedly for measurement and monitoring by members of the Galapagos National Park Service, Charles Darwin Foundation and visiting scientists.
But there is another side to the success story.
While the tortoise population is stable, it is not likely to increase until more of the landscape recovers from the damage inflicted by the now-eradicated goats.
“Population restoration is one thing but ecological restoration is going to take a lot longer,” he says.
After the goats devoured all the grassy vegetation and were subsequently removed from the island, more shrubs and small trees have grown on Española.
This hinders both the growth of cactus, which is a vital piece of a tortoise’s diet, and the tortoises’ movement.
Chemical analysis of the soil shows there has been a pronounced shift from grasses to woody plants on the island in the last 100 years.
The shrubs and trees also inhibit the movements of the endangered waved albatross whch breeds on the island.
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