Reptiles
Galápagos Tortoise
Chelonoidis niger · also called Galápagos giant tortoise
The Galápagos tortoise is the largest tortoise on Earth and a symbol of both the islands it is named for and the theory of evolution. A single ancestral tortoise that arrived from South America diversified into a set of distinct island forms, and that pattern was part of the puzzle Charles Darwin later assembled.
Overview
Giant tortoises live across the Galápagos archipelago, with most of the 15 recognised species restricted to a single island or, on large Isabela, a single volcano. On humid, well-vegetated islands they graze the highlands and migrate seasonally down to the lowlands along ancient trails. On arid islands they persist in the dry scrub, feeding heavily on cactus.
Two body plans
The most famous feature of the group is the split between two shell shapes:
- Domed tortoises — big, rounded, short-necked — live where food grows near the ground on lush islands.
- Saddleback tortoises have a shell raised into a high arch over the neck, along with longer necks and limbs, on dry islands where the staple food, prickly-pear cactus, grows tall. The cactus, in turn, has evolved taller, more tree-like trunks in response.
The Spanish word galápago, meaning saddle, gave the islands their name.
Life at low speed
Everything about a Galápagos tortoise is slow. It grows for 40 years before reaching full size, rests up to 16 hours a day, walks at a stroll, and can go months — even a year — without eating or drinking by metabolising body fat and the water stored in its tissues. When rain does fall, tortoises drink enormous quantities and wallow in muddy pools. This endurance is exactly what made them so vulnerable to sailors, who could keep them alive in a ship’s hold as a meat supply.
Reproduction
Males compete in the breeding season by facing off, stretching their necks up, and gaping — the taller reach wins, without contact. Females travel to dry lowland nesting areas, dig a hole with the hind legs, lay 2 to 16 hard-shelled eggs, and seal it with mud. Incubation takes four to eight months, and, as in many reptiles, nest temperature determines the hatchlings’ sex — warmer nests produce females.
Threats and recovery
Centuries of hunting and introduced animals cut the total population from perhaps a quarter of a million to around 15,000 by the 1970s, and at least two species were lost — the Pinta Island tortoise ending with the death of “Lonesome George” in 2012.
Since then the trend has reversed. Captive breeding and head-starting programmes have released thousands of young tortoises, goats have been eradicated from several islands, and one species thought extinct, the Fernandina tortoise, was rediscovered in 2019. The species is still Vulnerable, but for the first time in centuries its numbers are climbing.
Galápagos Tortoise: common questions
How long do Galápagos tortoises live?
They are among the longest-lived land animals. Wild tortoises commonly pass 100 years, and captive individuals have lived much longer — Harriet, held in Australia, was estimated at 175 when she died in 2006, and "Lonesome George," the last Pinta Island tortoise, was around 100. Their slow metabolism, large size, and lack of natural predators all contribute.
What is the difference between a domed and a saddleback tortoise?
The two shell shapes match two habitats. On large, wet, highland islands with ground-level plants, tortoises have high, rounded "domed" shells and short necks. On small, dry, low islands where the main food is tall cactus, tortoises evolved "saddleback" shells that flare up at the front like a saddle, plus longer necks and legs, letting them reach browse well above the ground.
How did Galápagos tortoises influence Darwin?
During the Beagle's 1835 visit, the vice-governor of the islands told Charles Darwin that he could tell which island any tortoise came from by its shell. Darwin did not grasp the significance at the time, but the idea that a single ancestral tortoise had diversified into distinct island forms — like the islands' finches and mockingbirds — became part of the evidence for evolution by natural selection in "On the Origin of Species."
Why did tortoise numbers collapse?
From the 1600s to the 1800s, whalers, sealers, and buccaneers took an estimated 100,000–200,000 tortoises as fresh meat, stacking live animals in ships' holds where they survived for months without food. Settlers then hunted them and cleared land for farming, and introduced goats stripped their food while rats, pigs, dogs, and cats ate eggs and hatchlings. Several species were wiped out entirely.