Galapagos Tortoise

Quick Take

• The Galapagos tortoise invites birds to clean its skin, and then it sometimes turns around and eats them. See the symbiotic behavior →
• Some of the plants this tortoise casually munches would literally burn your skin. Explore the tortoise's diet →
• The shell looks impossibly heavy, yet its real structure is something most people would never guess. Discover the shell anatomy →
• A population of just a dozen individuals was all that stood between one tortoise subspecies and total extinction. Here's what happened next. Trace the recovery effort →

Evolving over millions of years in its remote island habitat, this tortoise had almost no contact with the outside world until the discovery of the island by humans in 1535 led to rapid changes with which the tortoise could not cope. Only an immense conservation effort saved them from extinction.

5 Incredible Galapagos Tortoise Facts

• Galapagos actually means tortoise in Spanish, though the word galapago also carries a secondary meaning related to saddle.
• The shell of the tortoise may look solid, but it is actually composed of a honeycomb-like structure that weighs less than it appears.
• The tortoise first came to the Galapagos between six and twelve million years ago from South America. Although they aren’t great swimmers, the evidence suggests that tortoises have the ability to remain buoyant in the water and keep from drowning.
• Because of their poor hearing, the Galapagos tortoises rely on their vision and smell to sense their surroundings.
• One of the more interesting facts is that the Galapagos tortoise appears to have a beneficial relationship with some species of finches and mockingbirds. These birds feed on the parasites clinging to the tortoise’s skin and receive a free meal in turn. The tortoises anticipate this and even stretch out parts of their body for the birds to access. However, the tortoise has been known to betray the bird and eat it instead.

Evolution and History

It is believed that these tortoises arrived on the island chain between 6 and 12 million years ago, and they probably drifted on piles of vegetation functioning like rafts across the 600 miles of ocean, or they drifted on their own. Once there, they developed into two general carapace styles with either a domed shell or a saddle-backed shell (or a shell somewhere in between).

There is a strong connection between many of the living creatures of the Galápagos Island Chain and the concept of evolution itself. Charles Darwin’s visit to the island inspired his groundbreaking theory concerning natural selection. Because of their similarities and differences, the tortoises were an apt example of how species evolve from common ancestors.

Classification and Scientific Name

The scientific name of the Galapagos tortoise is Chelonoidis niger, which simply means black, although this species has more of a gray-green color. There is a collection of several distinct subspecies all existing under a single taxonomy. Each subspecies occupies a different part of an island or a different island altogether.

Charles Darwin, when he made his famous voyage aboard the Beagle in the 1830s, remarked on the amazing diversity of tortoise species on the various islands of the Galapagos by saying that these tortoises were like “inhabitants of some other planet.” There were about 15 distinct taxonomic groups of tortoise populations at Darwin’s time, but only about 11 exist today. There is also some debate about whether certain populations arose as a result of several colonization events to the island or whether all of them descended from a single colonizer.

The Galapagos tortoise belongs to the family of land-dwelling tortoises, Testudinidae. This taxonomic classification is based on its anatomy, genetics, and evolutionary history.

There are several subspecies spread throughout the island chain, including the following:

• Volcan Wolf Tortoise (Chelonoidis nigra becki): The Volcan Wolf tortoise has adapted two different body carapace types, the domed and the saddle-backed, that are both found throughout the islands in different subspecies. This is probably due to a lava barrier that separated populations and then a blending of them later on. Like all Galapagos Tortoises, there have been efforts to increase population numbers and conserve this great species. It is estimated that between 10,000 and 12,000 individuals remain in the wild.
• Chatham Island Tortoise (Chelonoidis nigra chathamensis): The Chatham Island tortoise had much of its territory damaged by dogs and donkeys brought to the island by humans. Efforts to bring back the numbers of this breed have worked well, and their numbers are close to 7,000 individuals. Their carapace is black, wide, and somewhere in between the domed shape and the saddle-backed shape of its cousins.
• Santiago Island Tortoise (Chelonoidis nigra darwini): The Santiago Island Tortoise had a population that was severely reduced, much like the other tortoises on the islands, due to hunting and the introduction of foreign animals, like goats. The numbers have grown due to conservation steps to nearly 1,200 individuals. Their dark gray shells are in between the domed and saddle-backed variations of their species, with flared sides that are somewhat serrated.
• Eastern Santa Cruz Island Tortoise (Chelonoidis nigra donfaustoi): The Eastern Santa Cruz Island tortoise makes up one of the two distinct subspecies on the island and, like their cousins on the western part of the island, has a domed, black, oval carapace. There are only 400 or so left on the island.
• Duncan Island Tortoise (Chelonoidis nigra duncanensis): The Duncan Island tortoise was one of the lucky subspecies that were not as badly hunted as others; however, their numbers were greatly reduced later in the 1900s due to expeditions on the island and the introduction of rats into their environment. Because of a breeding program, this subspecies was able to recover and reproduce in the wild. Over 1,700 tortoises have now been repatriated to the island. Their shells have a brownish, gray tint which is long and somewhat shallow.
• Sierra Negra Tortoise (Chelonoidis nigra guentheri): The Sierra Negra tortoise has been one of the more endangered subspecies on the island. They have recovered after overhunting to have numbers close to 700 today. In fact, a group was removed into a breeding, protected program due to the threat of a nearby volcano. They are known for their flat-topped shells that are domed in the middle and saddle-backed.
• Hood Island Tortoise (Chelonoidis nigra hoodensis): The Hood Island tortoise is one of the best turnaround stories for this giant reptile. Due to overhunting in the 1800s, the population of the Hood Island tortoise was reduced to just a few members. Amazingly, about a dozen remaining tortoises were collected to be held at the Charles Darwin Research Station and have been able to recover. Around 1,000 tortoises now inhabit Hood Island. These tortoises have a shell with a large cervical indentation, and they are saddle-backed and black in color.
• Volcan Darwin Tortoise (Chelonoidis nigra microphyes): The Volcan Darwin tortoise, like many of its relatives, was almost wiped out of existence in the 1800s by whalers looking to sell their oil. Since then, numbers have recovered to almost 1,000 in the wild. These members of the family have a more brown tint to their oval shells, which are somewhere between saddle-back and domed.
• Fernandina Island Tortoise (Chelonoidis nigra phantasticus): The Fernandina Island tortoises sadly only have one remaining member, Fernanda, of the subspecies that we know about. However, there may be more members of this group still remaining that no one has discovered yet. The lone member is in captivity with strict protection for testing and conservation.
• Western Santa Cruz Island Tortoise (Chelonoidis nigra porteri): The Western Santa Cruz Island tortoises are divided into three groups on the island, and they have a domed, black, oval carapace.
• Volcan Alcedo Tortoise (Chelonoidis nigra vandenburghi): The Volcan Alcedo tortoise has a black, domed shell and has been successful at reproducing in the wild despite the challenges all Galapagos Tortoises face. In fact, they hold the record for the biggest tortoise population of the whole group.
• Iguana Cove Tortoise (Chelonoidis nigra vicina): The Iguana Cove tortoise is a subspecies that has been reduced over the last couple of centuries but has managed to grow back to around 2,500 tortoises through preservation efforts. They have one of the thicker, sturdier shells, with a shape that lands somewhere between the domed and saddle-backed types.

Appearance

The Galapagos tortoise is one of the largest species of tortoise in the world. Males can weigh more than 500 pounds and reach 6 feet in length, while females weigh a comparatively smaller 250 pounds. The giant shell is obviously the most important characteristic of the tortoise’s anatomy. This massive structure is fused to the ribs and covered in segmented horny scutes. The bands on the shell cannot be used to determine the animal’s lifespan, since they wear off over time.

The tortoise’s shell has two types of adaptations. The domed shells, which are completely round, restrict the movement of the head. These tortoises live in humid areas with diverse vegetation within reach. The saddleback shells curl up near the neck, which allows them to stretch out their necks and feed on higher vegetation. When these tortoises live in arid regions where the vegetation is sparser, and the tortoises must work harder to reach it.

Behavior

Restricted in what it can do by a slow metabolism, the Galapagos tortoise leads a rather sluggish life. It sleeps up to 16 hours a day and then spends the rest of the time either feeding or resting. As a cold-blooded reptile, the tortoise lacks the adaptations to properly regulate its internal body temperature, so it must spend a lot of time wallowing in mud, soaking in water, or exposing its body to the rays of the sun.

One of the more interesting facts is that the Galapagos tortoise can migrate between different elevations of the island throughout the day in response to temperature. These tortoises maintain a very specific, regimented schedule from which they hardly deviate. By following the same routine every day, their heavy bodies carve out distinctive paths in the landscape which become semi-permanent features.

The Galapagos tortoise is slow and cumbersome, but the size of an adult obviously confers an enormous advantage against most predators. When it’s seriously threatened, the tortoise will pull back into its shell for protection, but contrary to some beliefs, it cannot leave the shell, since it is fused to the body.

The Galapagos tortoise does not appear to cooperate in any substantive way with other members of the same species, but it does tolerate their presence since they feed and rest in close proximity.

However, when mating season arrives, male tortoises engage in a competition by stretching out their heads. The tortoise with the higher head is considered to be the winner of this contest, and that is usually the end of it. But if the loser does not concede right away, then hostilities might break out into a bitter brawl, consisting of biting and nipping.

The Galapagos tortoise makes very few sounds except for hoarse grunts during copulation, harsh sounds during aggressive encounters, and a hissing noise made by the expulsion of air as the tortoise withdraws into its shell.

Habitat

The Galapagos is a hotspot of volcanic activity; it contains Volcan Wolf, Volcan Alcedo, and many others. The climate is generally hot and dry, but frequent spells of rainfall throughout the year do keep life flourishing. The El Niño weather event also buffets the island chain every three to seven years.

The Galapagos tortoise is endemic to the island chain of the Galapagos, about 563 miles west off the coast of Ecuador and an official part of that country.

Diet

The Galapagos tortoise is an herbivorous grazer that has many unique adaptations to cope with the difficult environment in which it lives. By storing excess resources in its body, the tortoise can go without food or water for an entire year.

What does the Galapagos tortoise eat?

The Galapagos tortoise eats many different types of fruits, flowers, leaves, and grass, some of which are so dangerous that they can burn human skin. The prickly pear cactus appears to be a particular favorite. Lacking teeth, the tortoise grinds up food with the tough outer parts of the mouth.

Predators and Threats

For millions of years, the Galapagos tortoise evolved in a habitat that was almost completely free of large mammals. Its sheer size and giant protective shell usually provided adequate protection against everything else. But after the discovery of the island, people indiscriminately hunted the tortoise for food and introduced non-native predators to the island. These new mammals either preyed on the tortoise directly or out-competed it for precious food.

What eats the Galapagos tortoise?

Before the arrival of people, the Galapagos hawk was the only creature to prey upon the juveniles and eggs. However, as people poured onto the island, they introduced pigs, cats, rats, and other species, which gorged on the eggs in enormous numbers, causing populations to plummet.

Reproduction, Babies, and Lifespan

During mating season, which usually lasts from January through August, the male will locate a female by her scent. He will then initiate courtship in a rather violent manner by ramming her with the front of his shell and then nipping at her legs. Once copulation is complete, the female may travel several miles to the drier lowlands and then deposit up to 10 eggs, each about the size of a tennis ball, into a 12-inch sandy hole in the ground. The temperature of the soil appears to play a role in determining the sex of the offspring, as hotter soil will lead to more females.

After an incubation period of about three to eight months, the young tortoises emerge from the eggs, measuring about 2.4 inches in size. Since they receive no other parental care, their first challenge is to dig their way to the surface, which takes about a month. The nutrient-rich yolk sac will sustain them for several more months, after which time they must learn to fend for themselves.

The Galapagos tortoise is an exceptionally slow-growing animal that takes about 20 to 25 years to fully mature, but they compensate for this with an incredible lifespan. The oldest recorded lifespan was more than 150 years. Unfortunately, most perish within the first 10 years of life.

Population

The Galapagos tortoise has been in a constant state of peril for centuries. Once common across the entire island chain before the 16th century, more than 100,000 were killed by pirates, hunters, and merchantmen who stopped at the island and stocked up on tortoises to sustain themselves on their journey.

Although hunting has largely ended, the tortoise still faces threats and competition from non-native animal species, causing populations to dwindle to a low of only 3,000 by the 20th century. The Pinta Island tortoise was officially declared extinct in 2012 upon the death of the last known male, Lonesome George, who became something of an international cause célèbre for conservation issues. All attempts to find a suitable female for him, including those of different species, were unsuccessful.

Since falling to this low point, it is estimated that populations have now climbed as high as 20,000 individuals, thanks in part to the fact that the Ecuadorian government has extended protection to the tortoise and carved out national park refuges. The Charles Darwin Research Station has also mounted an effort on the island to breed this species in captivity. But the long maturation times and lifespan also make it difficult to revive numbers quickly. No species has achieved better than Vulnerable status on the IUCN Red List, and a few are critically endangered.

In the Zoo

The San Diego Zoo is one of the top worldwide refuges for captive Galapagos tortoises. They received their first tortoises in 1928 to help establish a North American population and contribute to saving the species from extinction. Four decades later, this morphed into a partnership with the Charles Darwin Research Station to help rear tortoises in captivity. The tortoise is also found at the Saint Louis Zoo, the Cincinnati Zoo and Botanical Gardens, the Houston Zoo, the Honolulu Zoo, the Philadelphia Zoo, and many others.