At first glance, you might not peg Diego as a ladies' man. He lumbers along slowly, extending his long, wrinkly neck and staring intently with his small, beady eyes.
But at 130-or-so years old, Diego has never had problems finding a mate. The Galapagos giant tortoise has such a high sex drive, in fact, that he has been credited with helping to save his species from extinction.
Diego was one of 15 tortoises in the captive breeding program on the island of Santa Cruz in Ecuador. Because Diego did such an impressive job, he and his fellow tortoises get to retire.
During the 40 years of the breeding program, the population went from 15 to 2,000 tortoises, according to a statement from the Galapagos Conservancy.
As many as 40% of the tortoises produced are thought to be descendants of Diego. He reportedly fathered more than 800 offspring as part of the breeding program.
Diego was one of many tortoises brought to the San Diego Zoo from an expedition to the Galapagos island of Española some time between 1928 and 1933. He was part of the zoo's breeding program for 30 years before he returned to Ecuador in 1977 to the Charles Darwin Research Station.
Why Diego has the spotlight
Although Diego is the tortoise making headlines, another male — known simply as E5 — actually has fathered about 60% of offspring, according to The New York Times. Yet, he hasn't received the same fanfare. (There's a third male, but he really hasn't done much of anything.)
What is it about Diego that causes such a stir?
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," James P. Gibbs, a professor of environmental and forest biology at the State University of New York in Syracuse, tells the Times.
Now that Diego's courting days are over, the plan is for Diego and his fellow tortoises to be released back into their natural habitat on Española in March 2020.
In addition to the breeding program, conservation efforts on the island are also being credited for the tortoise comeback. Projects have included eradicating introduced species and helping promote the growth of cactuses, which are an important food source for tortoises, according to a statement by Jorge Carrión, director of the Galapagos National Park.