The Namesake of the Islands

Since their discovery in 1535, the Galapagos Islands have been famed for their namesake --the giant tortoise (Geochelone elephantopus). The word "galapago" in Spanish means "saddle" and refers to the carapace, or shell, of these huge reptiles.

From island to island, giant tortoises vary in size and the shape of their shells. The smaller saddle-backs, with their long necks and limbs and a carapace raised in front, are well adapted to the environment on lower, drier islands. Although they prefer to eat fallen cactus pads and low growing vegetation, when these are unavailable, they must reach up for the leaves of taller shrubs. Larger, dome-shaped tortoises are typical of higher, lusher islands, where they feed on grasses, other low-growing plans and fallen fruit.

The 14 subspecies of Galapagos tortoises all evolved from a common ancestor. Nine of these evolved separately, on individual islands. The remaining five are from the large island of Isabela -- each geographically confined to one of the islands five major volcanoes. Today three of the subspecies are extinct. Sadly, a fourth subspecies, from Pinta Island, is represented by only one surviving male - "lonesome George."

Life Cycle of over 150 Years

Giant tortoises reach maturity at 20 to 30 years. They mate during the rainy season, usually between January and June. Then, between June and December, the females migrate to the arid zones to nest. While digging the hole with her hind legs, a task that can take several hours, the female urinates frequently to soften and bind the soil. Between two and twenty eggs are laid, each about the size of a tennis ball. After covering the nest, the female returns to the highlands, leaving the eggs to incubate for the next four to eight months. Nest temperature determines the sex of the hatchlings, with lower temperatures producing more males.

The young tortoises hatch between November and April, taking a month to dig their way out of the nest. These hatchlings weigh less than 1/1000th of what they will weigh as an adult. Hawks are probably the only native predator of young tortoises. If they survive the difficult first few years of life, when food scarcity is the major obstacle, they can live for over 150 years.

Past Populations Were Much Greater

Whalers and colonists killed over 100,000 giant tortoises for meat and oil during the 19th and 20th centuries. Visiting ships prized them as a source of fresh meat on long voyages -- stored in the hold, they survived up to a year without food or water. However, man is not the only concern. He came with domestic animals such as pigs, donkeys, goats and dogs as well as black rats. Over time, these introduced animals formed wild populations throughout the islands with devastating results.

Pigs root up tortoise nests to eat the eggs. On Pinzon Island, rats eat every hatchling. Dogs kill tortoises up to four years old. Goats compete for food, and donkeys trample nests. From the several hundred thousand tortoises that roamed the islands before man's arrival, fewer than 15,000 survive today.

Conservation Measures Help Protect Tortoise Populations

With the declaration of Galapagos as a National Park in 1959, the Islands' native wildlife became legally protected. Shortly thereafter, the Charles Darwin Research Station and the Galapagos National Park Service began intensive efforts to further protect endangered tortoise population with the establishment of a captive rearing center on Santa Cruz.

The Espanola subspecies is a special case. Reduced to only two males and twelve females, little or no natural breeding was taking place -- they were so dispersed on the island, they never met! Between 1963 and 1974, the Espanola tortoises were brought to the center. There, all eggs laid were carefully placed in incubators until hatching.  The young tortoises remained at the rearing center for about three years, until large enough for a safe return to the wild. By 1995, nearly 700 Espanola tortoises had been returned to their island.

Similar programs protect other tortoise populations from the threat of introduced animals. Eggs are collected from natural nests and brought to the center for incubation, rearing and eventual release. Today, nearly 2,000 tortoises have returned to their island of origin as a result of these efforts, and a second rearing center was opened in the early 1990's.

This is only half the battle -- the elimination of introduced animals is also critical. Since 1961, eradication programs have concentrated on wild pigs, goats, dogs and rats. These efforts are successful on some islands, but many serious problems still exist.