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
Tortoise numbers declined from over 250,000 in the 16th century to a low of around 3,000 in the 1970s. This decline was caused by overexploitation of the species for meat and oil, habitat clearance for agriculture, and introduction of non-native animals to the islands, such as rats, goats, and pigs. The extinction of most giant tortoise lineages is thought to have also been caused by predation by humans or human ancestors, as the tortoises themselves have no natural predators. Tortoise populations on at least three islands have become extinct in historical times due to human activities. Specimens of these extinct taxa exist in several museums and also are being subjected to DNA analysis. Ten species of the original 15 survive in the wild; an 11th species ("Chelonoidis abingdonii") had only a single known living individual, kept in captivity and nicknamed Lonesome George until his death in June 2012. Conservation efforts, beginning in the 20th century, have resulted in thousands of captive-bred juveniles being released onto their ancestral home islands, and the total number of the species is estimated to have exceeded 19,000 at the start of the 21st century. Despite this rebound, the species as a whole is classified as "vulnerable" by the International Union for Conservation of Nature.