Galapagos Giant Tortoise Poster

This giant tortoise gave us a questioning look as we passed him on a road in the highlands of Santa Cruz Island in the Galapagos Islands. The Galapagos tortoise or Galapagos giant tortoise (Chelonoidis nigra) is the largest living species of tortoise and the 14th-heaviest living reptile. Modern giant tortoises can weigh up to 250 kg; even larger versions, now extinct, roamed every continent except Antarctica and Australia. Today, they exist only the Galapagos Islands, and Aldabra in the Indian Ocean. The tortoise is native to seven of the Galapagos Islands, a volcanic archipelago about 620 miles (more than 1,000 kilometers) west of the Ecuadorian mainland. With life spans in the wild of over 100 years, it is one of the longest-lived vertebrates. Shell size and shape vary between populations. On islands with humid highlands, the tortoises are larger, with domed shells and short necks – on islands with dry lowlands, the tortoises are smaller, with “saddleback” shells and long necks. Charles Darwin’s observations of these differences on the second voyage of the Beagle in 1835, contributed to the development of his theory of evolution. 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 exploitation 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. Conservation efforts, beginning in the 20th century, have resulted in thousands of captive-bred juveniles being released onto their ancestral home islands, and it is estimated that the total number of the species 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 (IUCN).