The Galapagos Giant Tortoise
The Galapagos Giant Tortoise, or tortuga terrestre gigante, is a symbol of biodiversity, history, and conservation on the Enchanted Islands.
A wild Giant Tortoise at the Chato Ranch on Santa Cruz Island.
Biodiversity
These reptiles can grow to be over 500 pounds and live for well over 100 years. Males have concave bottom shells to assist in mating and tend to be larger than females. These giant reptiles are herbivores, eating leaves, grasses, and cacti. The shape of their shell actually correlates to their diet. Some species have saddle shaped shells to help their necks reach for cacti off the ground - other species have domed shaped shells to allow them to more easily eat flat grasses.
There were once 15 species of the tortoise, with only 11 remaining today. The last species to go extinct was the Pinta Island tortoise, which ceased to exist after the death of the famous Lonesome George in 2012. His body is now on display at the Charles Darwin Research Station on Santa Cruz Island.
The 15 individual species of tortoises are proof of allopatric speciation, or the process in which animals evolve over time in isolated environments. Geographic separation from other gene pools causes the original species to evolve into something new. The Galapagos Tortoise is a perfect example of this, and was observed by Charles Darwin on his famous 1835 expedition. He noticed that the tortoises on the various islands were different from the ones on the mainland of South America - and wondered if they all shared a common genetic ancestry. This example helped to formulate Darwin's Theory Of Evolution. Over time, other scientists began to theorize that the Galapagos Tortoise reached the Galapagos Islands 2-3 million years ago by drifting from the mainland of South America.
A saddleback Giant Tortoise at the Charles Darwin Research Station on Santa Cruz Island.
You can see that the saddle-shaped shell enables this tortoise to extend its neck upwards, allowing it to eat taller cacti in desert environments where grasses would not be present.
History
Galapagos Giant Tortoises were once so prevalent that they actually inspired the name of the Galapagos Islands. When Spanish sailors found the islands in the 1500s, they called them “Galapago” meaning saddle, a reference to the shape of the tortoise’s shell.
The tortoises can live up to a year without food or water, which you would think would aid in their survival. Unfortunately, once the explorers and pirates who came to Galapagos discovered this, they would bring the giant tortoises on board their ships for long journeys to use as fresh meat since they required no care. Because of this, the tortoises were heavily exploited by pirates and explorers, and their numbers began to dwindle.
When these same sailors would encounter problems aboard their ships, the tortoises would be the first to be thrown overboard for being too heavy. Scientists theorize that the dumping of the tortoises into the ocean actually caused many of them to drift to different islands, eventually reproducing and creating varying subspecies.
Human settlement on the isolated islands proved disastrous for the tortoises. The introduction of domesticated animals such as goats, dogs, cats, rats, and hogs was detrimental to tortoise populations. The invasive animals would trample eggs in nests, snack on hatchlings, and create new competition in the tortoise's vegetative habitats. To this day, these pests remain a problem. However, the only natural predator of the giant tortoise is the Galapagos Hawk, which preys upon the eggs in their nests.
A baby giant tortoise feeds on leaves at the Charles Darwin Research Station.
Conservation
Today, there are heavy conservation efforts to protect and evade extinction for the Galapagos Tortoise. During my trip to the islands, I was able to visit the Arnaldo Tupiza Breeding Center on Isabela Island as well as the Charles Darwin Research Station on Santa Cruz Island. At these centers you can see the tortoises in all stages of development - from teeny tiny babies (above) to giant adults. Typically, the tortoises stay at the breeding center until they are large enough to survive in the wild. In addition, places like the Charles Darwin Research Station collaborate with the authorities of the Galapagos National Park to make better conservation decisions.
We were also lucky to see plenty of Galapagos Tortoises in the wild! During a bike tour on Isabela Island we saw one (slowly) crossing the bike path; on Santa Cruz Island we visited the Chato Ranch where we saw dozens among the pastures. Much like most wildlife on the Islands, they rarely notice you - and if they do, they simply retreat slowly into their massive shells. Still, it’s never okay to touch or approach them. A minimum distance of 6 feet is required at all times for all wildlife on the islands.
A wild dome-shelled giant tortoise crossing a bike trail on Isabela Island.
Wild Galapagos Tortoises at the Chato Ranch on Santa Cruz Island.
You can see that the shell of the tortoise above is more dome-shaped, since this type of tortoise feeds on grasses low to the ground and does not need to extend its neck upward to eat cacti.
Seeing them in the wild was fascinating. Though they are large reptiles, they are docile and timid. As someone who has studied environmental science and ecology for so long, it felt like I was seeing stories from my evolution textbooks come to life.
Despite the damage done to these animals by humans of the past, the Galapagos Tortoise has remained a symbol of the unique wildlife that can be found on Galapagos. And because of robust conservation efforts, these tortoises will remain that symbol for many years to come.
Don’t worry - we weren’t actually touching it!
