Distribution: Galapagos Islands
Description: High convex shell and tough scales over legs. Feet are not webbed unlike turtles.
Size: Length - 1.5m (5ft) Weight: 140-180kg (300-400lbs)
Life Span: At least 100 years.
Diet: Grass, leaves and cacti.
One day in February 1535, a Spanish ship sailed from Panama bound for Peru. During the voyage a great storm arose and for the next eight or nine days the crew battled against towering seas and terrifying winds to keep their ship afloat. Eventually the storm abated and both the ship and its crew survived, but they had been blown far from their course and they were short of food and water.
Then, on March 10th an island was sighted which later proved to be just one of a group of thirteen major islands and many smaller islets, all of volcanic origin. The Spaniards were surprised to find many strange animals on the island, including great numbers of giant tortoises.
So impressed were they by these tortoises that they gave the island group the name Galapagos - a Spanish word for tortoise. To this day we know the islands as the 'Galapagos Islands'.
Because the islands of the Galapagos are of volcanic origin they were never part of a main continent. They simply rose from the sea-bed as a result of massive volcanic activity millions of years ago. The islands are situated about 600 miles to the west of Ecuador in South America, so there is no mainland mass anywhere near the islands.
Despite this fact, animals of many kinds have colonized the islands including many species of birds, giant lizards, seals and of course, the huge tortoise. Nobody is absolutely certain just how the tortoise arrived or how it spread to most of the islands in the group. Perhaps we will never know.
However, it does seem quite likely that the tortoise arrived by sea, floating on a natural raft of driftwood. We know that the tortoise can survive for long periods without food or water, so the theory is a reasonable one. This would not necessarily explain the fact that each of the islands in the Galapagos group has (or had) its own particular form of tortoise, each with a differently marked shell.
The giant tortoise sleeps for about sixteen hours each day and keeps cool either by taking mudbaths or by partly submerging itself in water. They can survive for long periods without drinking and obtain most of their moisture from the dew found on vegetation. Fresh young grass is the favourite food of the tortoise but in the drier regions of the Galapagos Islands this is often scarce so instead they feed on the Opuntia cactus.
Between the Galapagos tortoise and the finch there has evolved a special relationship. The finches like to eat the ticks and parasites from the tortoise's skin and the tortoise seems only too happy to let them do this. The finch hops in front of the tortoise to show that it is ready and the tortoise then raises itself up high on its legs and stretches out its neck so that the bird can reach the parasites.
Sexual maturity is reached at 20 to 25 years old. The male tortoise bellows loudly and bobs his head to attract a female. 10-20 spherical eggs, no bigger than a chicken's egg, are incubated for 2 months by being buried in sand or soil in range of the sun's rays. The baby tortoises when they hatch are 6cm long with soft shells and because of this predators such as crabs and birds find them easy prey. The tortoises grow slowly and even at 2 years old they are not much bigger than a man's fist. They will keep growing for about 40 years until they reach their full size.
Threats to the Galapagos Tortoise
From the moment humans discovered them, the future of the giant tortoises of the Galapagos was in question. First the Spanish sailors caught them and ate them. Then successive waves of pirates used them as a source of food. A prison colony was set up on the islands and further stocks of tortoises were taken. Sailors made a point of capturing a number of tortoises to use as fresh meat when their initial supplies went bad. The tortoises could live for a long time without water, so they were kept alive on the ships and given water only a short time before they were due to be eaten. Whalers were the next in line, and they too killed large numbers. The tortoises were killed and used a source of oil.
As all these different human invaders came and went, they left behind them a whole new set of animals that had been deliberately or accidentally introduced; dogs, cats, rats, pigs and goats etc. Many of the new inhabitants of the island affect the tortoise either by eating their eggs or destroying the vegetation eaten by the giant reptiles.
There were originally fifteen different subspecies of Galapagos giant tortoise each evolved to suit the conditions on the different islands. Five of the subspecies are now extinct. IUCN currently classifies the Galapagos Tortoise as Vulnerable.
The Galapagos giant tortoise is now strictly protected. Young tortoises are being raised in a programme by the Charles Darwin Research Station in order to help keep the remaining races from becoming extinct. Eggs are collected from places on the islands where they are threatened and when the young tortoises hatch they are kept in captivity until they are large enough to fend for themselves.
These captive breeding plans have been successful. There is still a problem, however, with the animals that have been introduced such as pigs, dogs and rats which dig up and eat the tortoise eggs and young hatchlings. Hopefully though with more research and careful protection the animal that gave its name to the islands will survive into the future.
Image: Tortoise (Galapagos) by Daniel Ramirez
Information sourced from:
The IUCN Red List of Threatened Species (2015), Chelonoidis nigra [online],
Available from: http://www.iucnredlist.org/details/9011/0 [accessed 18/08/2015].