 Efforts are now underway to repopulate islands formerly inhabited by tortoises to restore their ecosystems ( island restoration ) to their condition before humans arrived . The tortoises are a keystone species , acting as ecosystem engineers which help in plant seed dispersal and trampling down brush and thinning the understory of vegetation ( allowing light to penetrate and germination to occur ) . Birds such as flycatchers perch on and fly around tortoises to hunt the insects they displace from the brush . In May 2010 , 39 sterilised tortoises of hybrid origin were introduced to Pinta Island , the first tortoises there since the evacuation of Lonesome George 38 years before . Sterile tortoises were released so the problem of interbreeding between subspecies would be avoided if any fertile tortoises were to be released in the future . It is hoped that with the recent identification of a hybrid C. n. abingdonii tortoise , the approximate genetic constitution of the original inhabitants of Pinta may eventually be restored with the identification and relocation of appropriate specimens to this island . This approach may be used to " <unk> " Floreana in the future , since captive individuals have been found to be descended from the extinct original stock . 
