Can you imagine living 150 to 200 years as the giant Galapagos tortoise. These are the largest tortoises in the world and they weigh up to 660 pounds and four feet in length. Originally there were thirteen subspecies of this tortoise (Geochelone nigra) living on the Galapagos Islands.
Today the numbers of this huge reptile have been reduced to eleven subspecies. Five of the subspecies live on Isabela Island with the other six divided between the other islands. Lonesome George is the only known surviving male of the Pinta subspecies, therefore they are expected to become extinct shortly. There is great hope that there may be males other than George roaming about without scientific knowledge.
Appearance
Of course, the most noticeable part of the giant Galapagos tortoise is his huge shell which is made of bone. This shell or carapace is fused to the tortoises ribs and other bones forming his protective home. Any predator would have a tough time getting at this tortoise when he brings his legs and head into his shell.
The tortoise’s scute, external plates on the carapace (shell), is divided into three parts, the central, the coastal and the marginal. They keep the scute pattern for all of their life. Although, there are growth bands, these are difficult to discern the age of the tortoise as they wear out and are rubbed off.
The giant Galapagos tortoises appearance differ depending from which island they reside.
On the larger Islands of Santa Cruz and Isabela where the highlands are wetter and there is thick vegetation close to the ground, the tortoise carapace is more of a dome shape. They also have shorter necks and limbs, yet they are the largest of the island tortoises. However, the tortoises near the Sierra Negra volcano on the southern end of the Isabela Island has a “table top” shell that is flat on top.
In Espanola and Pinta, dryer islands, the carapace is higher over the neck and flared out over the back feet. Called saddleback tortoises, they have longer, thinner limbs most likely to reach the higher vegetation of this area. They are smaller with males averaging a weight of 119 pounds, and females 60 pounds.
In all species, the male has a concave undershell, making mating an easier process. And all of them keep the dull brown color shell and scales on their necks and legs without much variation.
Location
The Galapagos Islands are located west of Ecuador in South America. This is the natural habitat of the giant Galapagos tortoise. The island was named after these huge tortoises by Spanish explorers who thought the shells looked like the saddles they used called the galapago. According to the Charles Darwin Association, the original count of the giant Galapagos tortoise was 250,000. The population has dwindled to a mere 15,000 today.
During the 18th and 19th centuries many of them were killed off by whalers who used them as a food source. You see, these tortoises once turned on their backs could not right themselves, yet they would continue to live for months without food or water. This made for a fresh source of meat on the ships.
Another way these tortoises have been reduced is through the introduction of animals, such as goats, to the islands that would cause a loss of vegetation that the they needed to survive.
Diet
The giant Galapagos tortoise is herbivorous, plant eating, and eats primarily cactus, grasses, fruit and vines. They especially love fresh new grasses and the poison apple (Hippomane mincingly) which is extremely poisonous to humans. These tortoises can go for long periods without water as they acquire most of their liquid needs from moisture found in dew and vegetation sap. If they are unable to obtain any liquids, they can produce water by breaking down their body fat.
Those tortoises on the wetter islands migrate a bit by moving to the lower grassy plains after the rainy season and climb back to the mountains when the dry season hits.
Behavior
These cold blooded reptiles will bask in the sun for two hours in the early morning absorbing warmth and energy. After activity for eight to nine hours a day, they may sleep for up to sixteen hours in their preferred mud wallow or pool. Although, they can withstand long periods without water, they enjoy drinking and wading in it. When first coming upon a water area, the tortoise may dip his head in above his eyes and drink for some time.
The giant Galapagos tortoise appears very slow moving, yet for his size, he can move quite a span when he has a purpose, eight miles in two to three days.
He retains a symbiotic relationship with some of the other birds of the Galapagos Islands. The finch stands before the tortoise at which time the tortoise sticks out his neck and the finch pecks off ticks on his skin. Thus the tortoise is relieved of the pests and the finch gets dinner. Some birds, the hawk and flycatcher use the back of the tortoise as a lookout post to spy prey.
Reproduction
The mating season for the giant Galapagos tortoise is generally between the months of January and August. Although, the male tortoises are competitive for the “affections” of the females, they have a very democratic, nonviolent means of determining who will mate with the female. When two males appear, wanting to mate with the same female, they simply stand on their hind feet and determine who is the tallest. The tallest tortoise gets the girl and the other male tortoise leaves. Sexual maturity is not reached until the age of 20 to 25 years.
However, the males are not so smooth in the romance department. In order to get the female’s attention the male bobs his head and bellows at her. He then rams his shell into her and nips at her legs until she pulls them in, immobilizing her. Mounting the female from behind, mating can take several hours.
The female, after mating (during the latter half of the year), will move towards a dryer sandy area for nesting, usually near the coast. She may take several hours to dig her nest over a three or more day period. She will dig down approximately one foot, with her hind leg, and then lay between 2 to 16 hard shelled eggs. She covers the hole with a mixture of leaves, sand and urine constructing an incubator.
After an incubation period of 120 to 140 days, the tiny tortoises, each approximately 2.8 ounces, break through their shells and dig up to the surface which can take up to an entire month to accomplish. Once they are out in the open, their first hindrance is their predator the hawk. The prominence of the gender depends on the temperature within the nesting hole. If it is on the colder side, more males will be born, with a warmer nest, more females will be born.
