With his long leathery neck, dull-yellow face and beady eyes, there’s just something about Diego.
A tortoise more than 100 years old, Diego has had little trouble mating.
A member of Chelonoidis hoodensis, or the giant tortoise species from Española Island in the Galápagos in Ecuador, he was one of 15 tortoises in a captive breeding program at the Fausto Llerena Tortoise Center on the island of Santa Cruz.
Among the males, Diego displayed an exceptional sex drive, so much so, he’s credited with helping save his species from extinction.
Now, with the future secured, he gets to retire.
In a statement on Friday, the Galápagos National Park announced the end of the breeding program, saying an evaluation showed it had met its conservation goals.
The program began in 1965, with efforts first dedicated to saving the tortoise population on Pinzón Island, another island in the Galápagos. In 1970, researchers began saving the Española Island tortoises.
At the time, there were 14 tortoises left: 12 females and two males, according to the Galápagos Conservancy. In 1976, a third male was introduced to the tortoise restoration breeding program, Diego, who had lived at the San Diego Zoo in the United States for 30 years.
The breeding program helped increase the tortoise population to 2,000 from 15, Jorge Carrión, the director of the Galápagos National Park, said in a statement.
Paternity tests indicate that Diego is responsible for about 40 percent of the offspring produced, James P. Gibbs, a professor of environmental and forest biology at the State University of New York in Syracuse, said.
“Another more reserved, less charismatic male — ‘E5’ — has generated about 60 percent,” he said. “The third male — ‘E3’ — virtually none. So Diego has been critical.”
What was it about Diego? Why did he attract so many mates and garner such international attention, especially if another male was more productive?
Professor Gibbs says Diego has “a big personality — quite aggressive, active and vocal in his mating habits and so I think he has gotten most of the attention.”
“But it clearly is the other quieter male that has had much more success,” he added. “Maybe he prefers to mate more at night.”
Professor Gibbs said it was all about who the females select.
“It might come as a surprise to many but tortoises do form what we would call ‘relationships,’” he said. “The social hierarchies and relationships of giant tortoises are very poorly known.”
Mr. Carrión, the director of the national park, had a simpler explanation: “Without a doubt, Diego had some characteristics that made him special.”
Professor Gibbs said the giant tortoises became endangered because easy access to the island allowed whalers, pirates, fishermen and others to remove them for food primarily in the 1800s.
“Feral goats overran the island for many years and not only competed with tortoises for food, but also destroyed much of their habitat,” he added.
In an interview on Saturday night, Mr. Carrión said he believed Diego was taken from his home island of Española sometime in the 1930s.
Conservationists also worked on the ecological restoration of Española Island, including promoting the growth of cactuses, which are a source of food for the tortoises. That, in turn, helped bring the species from the brink of extinction, Mr. Carrión said.
The tortoises’ uniquely shaped shells allow them stretch to reach food. Diego, fully stretched out, extends about five feet. He weighs about 176 pounds.
The breeding program is a part of the Giant Tortoise Restoration Initiative, a collaborative effort led by the Galápagos Conservancy and the Galápagos National Park Directorate.
The tortoise center on Santa Cruz was established by the Charles Darwin Research Station in 1965, the Galápagos Conservancy said on its website. There are now three tortoise centers, which are all managed by the Park Directorate.
Relying on available data since 1960 about the island and its tortoise population, including a 2019 census, researchers developed mathematical models with projections for the next 100 years.
“The conclusion was that the island has sufficient conditions to maintain the tortoise population, which will continue to grow normally — even without any new repatriation of juveniles,” Washington Tapia, the Galápagos-based director of the Giant Tortoise Restoration Initiative, said in a statement.
Almost 80 years after he was taken, Diego is expected to return to Española Island in March.
The island is very dry, arid even, Mr. Carrión said, but to Diego, it’s home.
Johnny Diaz contributed reporting.