Courtesy of The Charles Darwin Foundation for the Galapagos and The Galapagos National Park Service
Giant tortoises can only be found on Galapagos and on the Aldabra Atoll in the Indian Ocean. They can weigh up to 270 kilograms, and they have very few natural enemies. However, these slow moving reptiles are threatened by humans and the animals humans have introduced on these remote islands.
Since the official discovery of Galapagos in 1535, the islands have been known for their namesake - the giant tortoise. The word "galapago" in Spanish means "saddle" and refers to the shell of these huge reptiles. From island to island, the tortoises vary in size and the shape of their shells. The smaller saddle-backs have long necks and limbs and a shell that is raised in the front. They are well adapted to the environment on lower, drier islands. Although they usually eat fallen cactus pads and low growing vegetation, they sometimes have to reach up high for taller shrubs, when the lower vegetation is unavailable. Larger, dome-shaped tortoises are typical for higher, lusher islands, where they feed on grasses, other low growing vegetation and fruits.
The 14 subspecies of Galapagos tortoises all evolved from a common ancestor. Nine of these subspecies evolved separately, on individual islands. The remaining 5 are from the large Island Isabela - each geographically confined to one of the island's 5 major volcanoes. Today 3 of the subspecies are extinct. Sadly, a 4th 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 - 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 2 and 20 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 4 to 8 months. Nest temperatures determine 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 1/1,000th 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, 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 4 years old. Goats compete for food, and donkeys trample nests. From 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 populations with the establishment of a captive rearing center on Santa Cruz.
The Espanola subspecies is a special case. Reduced to only 2 males and 12 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 3 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.
THEIR FUTURE IS IN YOUR HANDS
The Ecuadorian Government, Friends of Galapagos, World Wide Fund for Nature, United Nations Development Program, Frankfurt Zoological Society Help for Threatened Wildlife and other concerned institutions and individuals support the giant tortoises research and rearing program. Although much has been accomplished, much more remains to be done to ensure the survival of these seemingly timeless creatures.
It is possible that some of the giant tortoises we see today were there when Charles Darwin visited the Galapagos in 1835. With continued conservation efforts and supports, some of the tortoises that we marvel at today will be here for our grandchildren and their grandchildren to appreciate.