Galápagos Giant Tortoise (Chelonoidis niger): Facts and Lifespan

What does a Galápagos tortoise look like?

A Galápagos tortoise has a huge bony shell, dull brown, gray or nearly black, and often patched with lichens on older animals. The upper shell, or carapace, is fused to the ribs and backbone, so it is a living part of the skeleton rather than a separate case. The tortoise can pull its head, neck and front legs inside for protection.

The legs are thick, pillar-like and covered with hard, dry scales, giving the animal an elephant-like walk. The front feet carry five claws and the hind feet four. The neck can stretch surprisingly far, and the head ends in a toothless, horny beak used to crop plants.

The most famous difference between populations is the shape of the shell. On large, humid islands such as Santa Cruz, tortoises have a rounded domed shell, short necks and very large bodies. On small, dry islands such as Española and Pinzón, they have a saddleback shell, with the front edge raised high above the neck, together with longer necks and legs. Several islands have intermediate forms. The page Why do Galápagos tortoises have saddlebacks? explains how the two shapes evolved.

Males are larger than females and have longer, thicker tails. The lower shell, or plastron, of a male is curved inward, which helps him balance on top of a female during mating.

How big do Galápagos tortoises get?

The Galápagos tortoise is the heaviest living tortoise and the largest cold-blooded land animal alive today. Size varies a great deal between islands, so averages for the whole species can be misleading.

The heaviest reliably weighed individuals have passed 400 kg (880 lb), and Guinness World Records lists a captive male in Florida at 417 kg (919 lb). Tortoises keep growing slowly for several decades. For records, growth and the differences between islands, see How big do Galápagos tortoises get?

Island forms and taxonomy

The tortoises of the Galápagos are a classic example of a species complex: a group of closely related populations that have evolved in isolation. Scientists recognize about 14 to 15 named island forms. Twelve survive today. The forms from Floreana, Santa Fe and Pinta are extinct, although tortoises with Floreana and Pinta ancestry have been found among hybrids on Isabela Island.

Five of the surviving forms live on separate volcanoes of Isabela, the largest island, because lava fields and dry terrain keep them apart. Others live on Santa Cruz (which has two distinct lineages), Santiago, San Cristóbal, Pinzón, Española and Fernandina. The Fernandina tortoise was known from a single male collected in 1906 until a living female was found there in 2019.

Whether these forms are species or subspecies is still debated. From the 2000s many authorities, including the IUCN, treated each as a separate species, such as Chelonoidis porteri for the Santa Cruz tortoise. In 2021 the Turtle Taxonomy Working Group returned them to subspecies of a single species, Chelonoidis niger. Either way, each island population is genetically distinct and is managed separately.

DNA shows that all Galápagos tortoises descend from ancestors that drifted from mainland South America, probably carried by the Humboldt Current. Their closest living relative is the small Chaco tortoise of Argentina and Paraguay. The oldest islands, Española and San Cristóbal, appear to have been colonized first, with tortoises then spreading island to island.

Habitat and range

Galápagos tortoises are native to seven islands of the Galápagos archipelago, about 1,000 km (600 mi) west of mainland Ecuador. They live from dry, rocky lowlands dominated by cactus and thorny scrub to cool, misty highlands with forest, grassy meadows and rain-fed pools.

On the larger, wetter islands many adult tortoises migrate with the seasons. During the cool, dry season they climb into the green highlands, and when the rainy season turns the lowlands lush they walk back down. Some travel several kilometers each way, and the same routes have been used for so long that they form worn trails sometimes called tortoise highways.

Tortoises are cold-blooded, so they bask for an hour or two after dawn before feeding. In the heat of the day and on cool nights they rest in mud wallows, pools or shallow depressions. Wallowing may help them control body temperature and keep off mosquitoes and ticks.

What do Galápagos tortoises eat?

Galápagos tortoises are herbivores. They eat grasses, leaves, herbs, ferns, lichens, berries and fallen fruit, including the fruit of the poison apple tree and introduced guavas. On dry islands the pads and fruit of prickly pear cactus (Opuntia) are a staple food and an important source of water.

Tortoises get most of their moisture from plants and dew, and they can survive many months without drinking. When water is available they drink huge amounts at once and store it in the bladder. Their metabolism is very slow, which allows them to go without food for long periods.

Because they swallow fruit whole and wander long distances, tortoises are important seed dispersers. They also trample paths and graze open areas, so ecologists call them ecosystem engineers: their presence shapes the vegetation of whole islands.

Behavior and daily life

Galápagos tortoises spend most of the day grazing, resting and basking. They walk at about 0.3 km/h (0.2 mph) but can cover long distances over days. Domed tortoises on wet islands often gather in loose herds around pools, while saddleback tortoises on dry islands tend to be more solitary and territorial.

Tortoises rely mainly on sight and smell. When startled, a tortoise pulls in its head with a loud hiss, which is air forced out of the lungs, not a threat call. Males fight for dominance by rising up on their legs and stretching their necks as high as possible with mouths open; the shorter tortoise usually backs down.

Small birds such as Darwin’s finches and Galápagos mockingbirds pick ticks and other parasites from the skin. A tortoise signals that it is ready by standing tall and stretching out its neck and legs, giving the birds access to folds of skin it cannot reach.

Reproduction and life cycle

Galápagos tortoises can mate at any time of year, with a peak in the rainy season. Females then walk to dry, sandy nesting areas, sometimes several kilometers away, and dig a hole about 30 cm (12 in) deep using only their hind legs. A clutch contains up to about 16 hard-shelled eggs, each roughly the size of a billiard ball, and domed forms tend to lay larger clutches than saddlebacks. A female may lay one to four clutches in a season.

The sun incubates the eggs. As in many turtles, nest temperature affects the sex of the young: cooler nests produce more males and warmer nests more females. Hatchlings appear after four to eight months and may spend weeks digging up to the surface. Young tortoises of all island forms have domed shells; the saddleback shape develops with age.

Growth is slow. Captive tortoises reach maturity at about 20 to 25 years, and wild ones probably take longer, perhaps 40 years in some cases.

How long do Galápagos tortoises live?

Galápagos tortoises are among the longest-lived animals on Earth. Wild individuals are thought to live well over 100 years, and captive tortoises have reached an estimated 170 years. Harriet, who died at Australia Zoo in 2006, is often said to have been about 175, though a careful study of her history suggests about 170. For comparison with other turtles, see How long do turtles live? and the list of longest-living animals.

Adult tortoises have no natural predators, and in the past most probably died from accidents such as falls. Eggs and hatchlings face much greater risks, especially from introduced animals.

Predators and threats

Before people arrived, only the Galápagos hawk preyed on young tortoises. Humans changed that. From the 1600s pirates, and from the late 1700s whalers and fur sealers, took live tortoises as food for long voyages because the animals could survive in a ship’s hold for a year or more. More than 100,000 tortoises are thought to have been removed in the 1800s alone, and many were also killed for oil.

Settlers then cleared land for farming and brought goats, pigs, dogs, cats, donkeys, cattle and black rats. Pigs, dogs and rats eat eggs and hatchlings, while goats strip the vegetation tortoises need. From an estimated 200,000 or more tortoises before human contact, numbers fell to only a few thousand by the 1970s.

Conservation status and recovery

On the IUCN Red List the Galápagos tortoise as a whole is listed as Vulnerable, while many individual island forms are assessed separately as Endangered or Critically Endangered. It is protected by Ecuadorian law and listed on CITES Appendix I, which bans international commercial trade.

Recovery began in 1965, when the Charles Darwin Research Station and the Galápagos National Park started collecting eggs from threatened islands and raising the young in captivity until they were large enough to survive. The best-known success is on Española, where only 14 adults survived. They were brought together with a male called Diego, returned from the San Diego Zoo, and more than 2,000 young tortoises bred in the program were released back onto the island.

Eradicating goats from several islands and rats from Pinzón has allowed vegetation and tortoise nests to recover, and wild numbers were estimated at around 19,000 to 20,000 by the early 21st century. The loss of the Pinta Island form, whose last member was Lonesome George, remains the most famous reminder of what was lost.

Galápagos tortoises and Charles Darwin

Charles Darwin spent five weeks in the Galápagos in 1835 aboard HMS Beagle. Local officials told him they could tell which island a tortoise came from by its shape, but at first he paid little attention. Later, together with his observations of mockingbirds and finches, the island-to-island differences became part of the evidence that led him to his theory of evolution by natural selection.

Today the tortoises are the symbol of the islands, a major draw for visitors and a flagship species for conservation. They are closely related in lifestyle, though not in ancestry, to the Aldabra giant tortoise of the Indian Ocean, the only other surviving group of island giant tortoises.