 On the southern island of Española , only 14 adult tortoises were found , two males and 12 females . The tortoises apparently were not encountering one another , so no reproduction was occurring . Between 1963 and 1974 , all 14 adult tortoises discovered on the island were brought to the tortoise center on Santa Cruz and a tortoise breeding program was initiated . In 1977 , a third Española male tortoise was returned to Galapagos from the San Diego Zoo and joined the breeding group . After 40 years ' work reintroducing captive animals , a detailed study of the island 's ecosystem has confirmed it has a stable , breeding population . Where once 15 were known , now more than 1 @,@ 000 giant tortoises inhabit the island of Española . One research team has found that more than half the tortoises released since the first reintroductions are still alive , and they are breeding well enough for the population to progress onward , unaided . 
