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When only 15 of his species remained, Diego ensured their survival by fathering more than 800 offspring. Way to go, buddy!

Photo by Peter Swaine

Of the 15 subspecies of Giant Tortoises native to the Galapagos Islands, only 11 remain. Two centuries of exploitation resulted in the loss of nearly 200,000 tortoises. 3 species have been extinct for some time, and a fourth species lost its last member, Lonesome George, in June of 2012. Photo by Aaron Logan.

A species literally on the brink of extinction in the 1960s, the Galapagos Giant Tortoise has made quite a stunning come-back thanks, in part, to one rather productive male who is responsible for fathering more than 800 offspring, and is credited with restoring an estimated 40% of the species’ population. Diego, a member of the endangered Chelonoidis hoodensis subspecies of tortoise native to Española Island of the Galapagos Island chain, has become the face of the Islands’ conservation efforts and at more than 130 years old has played a pivotal role in the Galapagos National Park captive breeding program over the past several decades.

Diego was brought into captivity by Dr. Harry Wegeforth, founder of the San Diego Zoo, during one of two expeditions made to the Galapagos in 1928 and 1933. Diego remained at the zoo for more than 30 years before being recruited to participate in the breeding program, which was enacted following a declaration that the Galapagos tortoises of Española Island had become critically endangered. At the time, only 2 other males and 12 females remained in the wild. Diego joined these 14 companions at the Charles Darwin Research Station on Española Island in 1977, and has been working to help save his species ever since, fathering more than 800 offspring in that time. 

6 baby Galapagos Giant Tortoises gather on the sandy ground.
Baby Galapagos Giant Tortoises at the Charles Darwin Research Station. Photo by Aaron Logan

Of the 3 males originally brought into the breeding program, only 2 have been successful in producing offspring. Diego, prolific as he may be, has been outperformed from a reproduction standpoint by the tortoise dubbed E5. So why all the hype around Diego if he hasn’t been as successful? 

“Another more reserved, less charismatic male – ‘E5’ – has generated about 60% [of the offspring produced]”, said James P. Gibbs, a professor of environmental and forest biology at the State University of New York in Syracuse. “The third male – ‘E3’ – virtually none. So Diego has been critical.” According to professor Gibbs, Diego’s fame has come down to one rather important trait: his “big personality.” 

“[Diego is] quite aggressive, active and vocal in his mating habits and so I think he has gotten most of the attention,” said professor Gibbs. Furthermore, females are quite particular about who they select as mates. “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.”

Giant tortoises can live up to a year without food or water. Once their longevity was discovered, however, it was exploited by pirates, whalers, and fisherman who would keep the animals on board ships to use for their meat and oils during long voyages. Photo by Sara Yeomans.

The decimation of the Giant Tortoise populations throughout the Galapagos is credited to ease of access to the islands by pirates, whalers, and fisherman who would remove the tortoises for food. The introduction of black rats and goats to the environment also played a significant role, as the rodents would hunt tortoise babies shortly after hatching, wreaking havoc on their population, and the goats destroyed their habitat. 

“Based on the results of the last census conducted at the end of 2019 and all the data available since 1960 — both of the island and its tortoise population — we developed mathematical models with different possible scenarios for the next hundred 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,” said Washington Tapia, director of the GTRI.

“In addition to the recovery of the giant tortoise population, which went from 15 to 2,000 thanks to this program, the management actions implemented for the ecological restoration of the island — including the eradication of introduced species and the regeneration of cacti through Galápagos Verde 2050 project — have helped to ensure that the island’s ecosystems currently have adequate conditions to support the growing population of tortoises,” added the Director of the Galapagos National Park, Jorge Carrión.

Declared a success, the breeding program is now closing and Diego is set to retire and return home after more than 80 years in captivity. In a statement released by Galapagos Conservancy, the closure of the program will return all of the original 15 unique breeding adults that have made this jump back from the brink of extinction a possibility. These individuals will undergo a quarantine process over the next several months to prevent the risk of seed dispersal, which could introduce plants that are not native to the island. Release back to Española Island is planned for March 2020.