The Galapagos tortoise, also known as the Galapagos giant tortoise is the 13th heaviest reptile alive today and the largest existing of the species. ‘Galapagos’ comes from the Spanish ‘galapago’, which means ‘tortoise’. The Galapagos tortoise has a very high brown and light green shell. It blends in very well with its surroundings. It can quickly withdraw its head, legs and tail into its shell when it is too hot or feels that it is in danger. Its shell is very big and very bony. Galápagos tortoises come in two types: the largest, called ‘domes’, have big, round shells, and live on the larger, wetter islands, and the smaller ‘saddlebacks’, which have a shell that curls up in front the way a saddle does, live on smaller islands that have dry vegetation. The distinctive saddleback shell may enable this tortoise to reach higher vegetation, and this tortoise also has a longer neck and limbs.
The Galapagos giant tortoise inhabits just six Galapagos Islands, of an island chain 1,000 km from the Ecuadorian coast, namely, Isabela, Pinzon, Espanola, San Cristobal, Santa Cruz, and Santiago. The tortoises live in muddy puddles and wallows, preferably in sunny areas. Some may be found at rest under large overhanging rocks. When it is the hot and dry season, these animals tend to go to the cooler highlands, and in the rainy season they return to the lowlands.
Galapagos tortoises generally lead a lazy, peaceful life that centers around eating, wallowing in puddles or relaxing in the sun. Being cold-blooded, as other reptiles are, they like to warm up by soaking in the sun. At night, they might rest partially submerged in water, mud, or brush to stay warm during cool evenings. Wallowing in mud also serves to keep them cool during the day. These tortoises are very regular with their sleeping, eating, and nesting habits. An individual may shift occasionally inside its range, but never moves to a different place. For traveling to feed in the volcanic highlands, this is such a regular habit that paths carved by the passage of thousands of tortoises are built into the landscape. Behavior like this is also a sort of social system, because the tortoises travel to the lakes together to swim lazily, always returning in groups. Another very regular habit is nesting. Females return to the exact same place each year to lay eggs.
Little information is known about the mating system in Galapagos tortoises. However, like other tortoise species, they might exhibit polygynous (one male to many females), polyandrous (one female to many males) or polygynandrous (promiscuous) (both sexes have multiple mates) mating systems. Mating is at any time during the year, peaking from January to August. Males generally become territorial in the mating season, at which time rivals stand tall and stretch their necks out to size each other up, with the taller tortoise typically being dominant. 2 - 16 eggs are laid in a nest that has been dug into sandy ground and then covered over with leaves and soil. The gestation period is 100 - 200 days. The young dig their way out once they have hatched. They are left on their own, and many of them die during the first few years. Their gender can be determined at 15 years of age. They reach maturity at 20 - 25 years old and their full adult size when they are 40 years old.
When mariners first arrived in the 1600s in the Galapagos Islands they captured these tortoises and kept them alive on ships to eat. Throughout the 19th century a great number of tortoises were taken by whaling ships for food, others being killed for their oil. Today what threatens them the most are the introduced species: feral cats, dogs and rats eat juvenile tortoises before their shell has fully developed, and goats and cattle are in competition for vegetation.
According to the San Diego Zoo Global resource, the total population size of the Galapagos tortoise is around 10,000 - 15,000 individuals. According to the Our Endangered World (OEW) resource, the total population size of this species is around 19,000 individuals, possibly more. The remaining subspecies of tortoise range in IUCN classification from extinct in the wild to vulnerable.