A breeding program for the Galápagos’ Española tortoises has ended after more than 40 years. Española Island is now home to a stable population of 2,000 Española tortoises, recovered from only 12 females and three males in 1976.
The program started with only two male tortoises until a third, named Diego, was found in the San Diego Zoo. He had lived in the zoo for about 30 years before joining the breeding program on the Galápagos’ Santa Cruz island. Diego, now over 100 years old, had a big impact on the program; he has a strong personality and isn’t shy about sex, which earned him a reputation online. Now, he and the 14 other tortoises in the breeding program are preparing to return home.
Genetic testing of the young tortoises living on Española island, which has been done regularly since the 1990’s, revealed that Diego fathered about 40 percent of them. Another tortoise, called E5, is responsible for the other 60 percent. The third male, E3, has produced very few offspring.
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,” says conservation biologist James P. Gibbs to the New York Times’ Aimee Ortiz. But he says the “more reserved, less charismatic male… has had much more success. Maybe he prefers to mate more at night.”
The recovery of the Española tortoises has been a decades-long battle. The giant tortoises were depleted from the island, hunted by sailors, whalers, and pirates for food, and goats were introduced. So before young tortoises could be restored on the island, conservationists had to contend with goats between the 1970’s and 1990’s. But cohorts of young turtles were released once or twice each year, with a survival rate of over 50 percent. By 2010, tortoises were once again a common sight on the island, Rory Carroll reported at the time for the Guardian.
"During the expedition we found nests, recently hatched tortoises, and adults born on Española, which indicates that the tortoise population is doing well,” Washington Tapia, director of the Galápagos Tortoise Restoration Initiative, told Carroll in 2010.
The breeding program had been running for years before the ancestry of juvenile tortoises was ironed out, Kacey Deamer reported for Live Science in 2016 when Diego’s libido last went viral. On Santa Cruz, the 15 breeding tortoises were kept in two corrals—Diego and E3 in one space with half of the females, E5 and the other females housed in another. Scientists gathered the eggs, and after incubating and rearing the tortoises for five years, they released the juveniles back to Española island.
The decision to end the breeding program comes after the 2019 census of Española island. The census and models of the next 100 years of tortoise population on the island found that “the island has sufficient conditions to maintain the tortoise population, which will continue to grow normally — even without any new repatriation of juveniles,” Tapia, said per a translation of the original statement.
It will take a few months for the breeding program to fully wind down. The 15 breeding tortoises will be quarantined to ensure that they don’t carry non-native seeds with them to Española Island. But in March, after at least 80 years away, Diego can retire on his home turf.