Aldabra giant tortoise
Large tortoises are among the longest-lived animals. Some individual Aldabra giant tortoises are thought to be over 200 years of age, but this is difficult to verify because they tend to outlive their human observers. Adwaita was reputedly one of four brought by British seamen from the Seychelles Islands as gifts to Robert Clive of the British East India Company in the 18th century, and came to Calcutta Zoo in 1875. At his death in March 2006 at the Kolkata (formerly Calcutta) Zoo in India, Adwaita is reputed to have reached the longest ever measured lifespan of 255 years (birth year 1750). Today, Jonathan, a Seychelles giant tortoise ("A. g. hololissa"), is thought to be the oldest living giant tortoise at the age of years and Esmeralda is second at the age of years, since the death of Harriet at 176, a Galapagos giant tortoise. Esmeralda is an Aldabra giant tortoise.
Galápagos tortoise
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 species 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. 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 "retortoise" Floreana in the future, since captive individuals have been found to be descended from the extinct original stock.The Galapagos Tortoise Movement Ecology Programme is a collaborative project coordinated by Dr Stephen Blake of the Max Planck Institute for Ornithology. Its goal is to assist the Galapagos National Park to effectively conserve giant tortoises by conducting cutting-edge applied science, and developing an inspirational tortoise-based outreach and education programme. Since 2009, the project team have been analysing the movements of giant tortoises by tracking them via satellite tags. As of November 2014, the team have tagged 83 tortoises from four species on three islands. They have established that giant tortoises conduct migrations up and down volcanoes, primarily in response to seasonal changes in the availability and quality of vegetation. In 2015 they will start to track the movements of hatchling and juvenile tortoises, supported by the UK's Galapagos Conservation Trust.