Giant turtle — one of the animal species most commonly associated with the Galapagos Islands. Thought to be descended from tortoises from a continent that washed ashore in the Galapagos thousands of years ago, there are now several subspecies endemic to the various islands. They can live for over a hundred years and are inextricably linked to the human history of the islands.
Origin of the species and description
Two things in particular stand out about giant tortoises: their size and their longevity. A male giant tortoise can grow to over 200 kg and can carry an adult human on his back quite easily. The exact lifespan of a wild Galápagos tortoise is unclear, but is likely between 100 and 150 years. An adult Madagascar tortoise given to the Queen of Tonga in the 1770s died in 1966. They reach sexual maturity only at the age of 20 to 30 years.
Video: Giant tortoise
Another rather interesting aspect of — it is the difference in the races inhabiting the different islands. Initially, there were 14 races, each of which lived on a separate island. Two races, the Floreana and the Santa Fe, died out by the middle of the eighteenth century. The Fernandina race became extinct in the twentieth century. Only one individual, a male named «Lonely George», survived in the Pinta race. The Hispanola race was very close to extinction, it is recovering thanks to the breeding program of the Darwin Research Station.
Giant tortoises display “gigantism”, a condition apparently aided by long periods of isolation when predation is almost non-existent and food sources are plentiful. However, it is likely that this was to some extent a pre-adapted condition, as large individuals would have been more likely to survive the journey despite osmotic water loss and the ability to tolerate arid climates. Fossil giant tortoises from mainland South America support this view.
Appearance and Features
There are many subspecies of giant tortoises that are found on different islands and have different species. Those that live on larger islands where there is more rain have “dome” shaped shells, while those that live in drier conditions are smaller turtles and have a “saddle” shell.
Turtle shells come in two main varieties, dome shaped and saddle shaped. Domed turtles are larger and live on islands where vegetation is more abundant. Smaller turtles with a saddle-shaped shell inhabit islands with less vegetation, such as Pinzon and Espanola. Saddle shape — this is an adaptation that allows the turtle to extend its neck, allowing it to walk higher than their dome-shaped shell brethren.
Turtles with domed shells lack an angle to the front of the shell (shell), which limits the extent to which they can raise their heads. They tend to live on large, wet islands where there is a lot of vegetation. Saddleback turtles have a curve from the top to the front of their shell, which allows them to stretch out to reach higher growing plants. They tend to live on dry islands in the Galapagos where food is less plentiful.
Fun fact: Giant tortoises live up to the name “giant”, reaching a weight of up to 400 kg and having a length 1.8 m. In captivity, they can become much larger than in the wild.
Where does the giant tortoise live?
Galapagos giant tortoise — one of the most famous animals on the islands, and the archipelago itself is named after them (Galapago — old Spanish word for turtle). The giant tortoise arrived in the Galapagos Islands from mainland South America 2-3 million years ago, where they were divided into 15 species, differing in their morphology and distribution. Since the death of Lonesome George in 2012, the last tortoise on Pinta Island, there are probably ten living species left in the Galápagos. Their arabulation is currently estimated at 20,000 people.
Fun fact: A related subspecies of the Galápagos tortoises is also the Seychelles giant tortoise (Aldabrachelys hololissa), which is thought to have gone extinct in the mid-1800s.
Turtles, from which the name Galapagos is derived, have become symbols of the islands, their unique fauna and threats to them. The only other species of giant tortoises located halfway around the world lives in the Indian Ocean in Madagascar and the Seychelles.
The highlands of Santa Cruz and Alcedo Volcano on Isabela are home to the largest number of giant tortoises. Populations can also be found in Santiago, San Cristobal, Pinzon and Espanola. Galapagos giant tortoises are present all year round. They are most active at noon during the cool season and early in the morning or late afternoon during the hot season.
Now you know where the giant tortoise is found. Let’s see what this reptile eats.
What does the giant tortoise eat?
Giant tortoises are vegetarians and are known to feed on more than 50 plant species in the Galápagos, including grasses, leaves, lichens, and berries. They eat between 32 and 36 kg per day, most of which is indigestible. They move slowly and apparently aimlessly, eating what they find.
Galapagos tortoises can walk for long periods without drinking water, up to 18 months. This is a great asset in nature, but it also made giant tortoises even more attractive prey for sailors. Compared to dry biscuits and salted pork, fresh turtle meat was a great treat. The sight of upside-down tortoises tied to decks and squirming for months apparently did not affect their appetites.
Fun fact: Many giant tortoises are migratory: they move within their habitat at different times year, following the rains to the greenest places where food is most abundant.
When they are thirsty, they can drink large amounts of water and store it in their bladder and pericardium (which also makes them useful sources of water on ships). In drier areas, prickly pear cacti are an important source of food and water. They have also been shown to lick dew off boulders on drier islands, even resulting in depressions in the rock.
The giant tortoise spends an average of 16 hours a day resting. The rest of the time they spend eating grass, fruit and cactus pillows. They love to swim in the water, but can live up to a year without food or water. Small birds such as finches are often seen perched on the backs of giant tortoises. Birds and turtles have formed a symbiotic relationship in which birds peck at mites from the folds of turtle skin.
Being ectothermic (cold-blooded), they need to bask for an hour or two to absorb the heat of the morning sun before grazing up to 9 hours a day. On drier islands, turtles migrate to greener pastures, creating well-defined paths known as «turtle roads». On the lusher islands, domed turtles often congregate in social groups, while saddleback turtles on drier islands prefer a more solitary existence.
Fun fact: Mud and water pools are often filled with wallowing turtles. This can help protect them from parasites, mosquitoes and ticks. Dust baths in loose soil also help to resist parasites.
Giant tortoises are known to have a mutualistic relationship with the special Galapagos finches, which remove annoying ectoparasites. The finch jumps in front of the turtle’s face to start cleaning. The turtle rises and expands its neck, allowing finches to peck at its neck, legs, and skin between the plastron and shell.
Social Structure and Reproduction
Giant tortoises reach puberty between 20 and 25 years old, and when the right moment comes, the male will sit on the female and stretch his long tail under her tail, in which his penis is located.
The underside of the male shell is convex, so it fits snugly against the rounded dome of the female and does not slip off.
Interesting fact: The male Galapagos tortoise is very noisy, and its grumbling in the distance can be heard at a distance of about 100 meters. Hormone-filled males have been known to pick up rocks, mistaking them for willing females. No wonder there is no record of this behavior leading to offspring.
Mating can occur at any time, but usually between February and June. Females travel several kilometers to nest in dry, sandy coastal areas. Using her hind legs, she digs a deep cylindrical hole and lays her eggs. Dome-shaped females dig 2-3 nests per year, 20 eggs per nest. Saddleback females living in harsher environments dig 4 to 5 nests per year, averaging 6 eggs per clutch, to spread the risk. In each case, she retains sperm from 1 copulation and uses it to fertilize multiple batches of eggs.
Fun fact: Nest temperature determines the sex of the young, with warmer nests producing more females.
After 4-8 months, young individuals emerge from the eggs and dig them to the surface. They stay in warm, low-lying areas for the first 10-15 years. If they survive the first dangers of extreme heat, the crevice, hungry sailors and hawks of the Galapagos Islands, they are likely to live to old age.
Giant tortoises natural enemies
Giant tortoises are natural enemies :
- rats, pigs and ants that prey on turtle eggs;
- wild dogs that attack adult turtles;
- cattle and horses, that trample nests;
- goats that compete with turtles for food.
They are also affected by barriers to migration such as farmland and road fencing, and may have health problems from being in close proximity to farm animals.
The greatest predators that giant tortoises have seen are undoubtedly humans. That their population today is only 10% of their estimated peak says a lot about the sheer number of people killed for food and oil over the past few centuries. According to the 1974 census, their number reached 3060 individuals. Early human settlements accelerated population decline as they were hunted and their habitats cleared for agriculture. The introduction of alien species has been as devastating to giant tortoises as it has been to many other endemic species.
The populations of the giant tortoise in the Galapagos Islands have been greatly reduced due to exploitation by whalers, pirates and fur hunters. Turtles provided a source of fresh meat that could be stored on a ship for months without food or water. This resulted in the loss of 100,000 to 200,000 turtles. They were also exploited for their oil, which could be used for burning in lamps. Human introduction of several species has further devastated turtle populations.
Population and species status
Giant tortoises were highly prized by the pirates and whaling ships that frequented the islands from the 17th to the 19th century, as they could be kept on ships for months, thus providing fresh meat and supplementing what must have been a very boring diet. In the nineteenth century, as many as 200,000 turtles may have been taken. Several races have become extinct, and the number of other races has been greatly reduced. Now only about 15,000 individuals live in the Galapagos. Of these, about 3,000 live on the Alcedo volcano.
Galápagos giant tortoises are currently considered “Vulnerable” by the International Union for Conservation of Nature, and many initiatives are currently underway to save the various subspecies. The dangers are still present and it is estimated that over 200 animals have been killed by poachers in the last couple of decades. As the population and tourist numbers grow, the pressure continues.
If you visit the Darwin Center in Santa Cruz, you will see the ecological conservation efforts. The young are reared and returned back to the wild on the islands where their subspecies live. Slow growth, late puberty, and island-specific endemism mean that giant tortoises are particularly susceptible to extinction without the intervention of conservationists. As a result, this inspiring creature has become a staple for conservation efforts in the Galápagos.
The number of wild giant tortoises in the Galápagos has been greatly reduced. Their population is estimated to have been around 250,000 in the 1500s when they were first discovered. However, the turtles have been saved from extinction through captive breeding programs, and it is hoped that conservation programs will continue to help their populations thrive.
Giant Turtle Conservation
Although the number of giant tortoises in the Galápagos Islands is starting to increase, they remain under threat from human impacts, including invasive species, urbanization and land use change. Therefore, understanding the ecological needs of turtles and including them in landscape planning will be essential to their successful conservation.
Since the establishment of the Galápagos National Park, eggs have been collected from the wild and incubated at the Charles Darwin Research Station. Keeping newly hatched turtles in captivity allows them to grow large enough to avoid being attacked by rats and dogs once they are released.
Eradication campaigns are underway to remove introduced species that threaten the survival of giant tortoises. The Ecological Program of the Galapagos Turtle Movement, led by Dr. Steven Blake, aims to carry out several research tasks.
- Identification of the spatial needs of the Galapagos giant tortoises;
- understanding the ecological role of the Galapagos giant tortoises;
- assessing how turtle populations change over time, especially in response to threats and management interventions;
- understanding the impact of human activities on turtle health.
The tracking team uses both traditional survey methods (such as behavioral observations) and high-tech methods, such as attaching tags to turtles to track their migration. So far, they have tagged individuals from four different species of turtles — including two species on Santa Cruz and one species on Isabella and Espanola.
Galapagos giant tortoises are one of the many species affected by the increase in the population of the Galapagos Islands, so the team is actively involved in advocacy and education initiatives. For example, they are working closely with key stakeholders to understand how turtles interact with the human population in order to reduce conflict between turtle and human. They also involve younger generations in their research initiatives as well as helping to spread their work to the local population.
Giant tortoises are the largest living tortoise species on Earth, which can weigh up to 300 kg in the wild (more in captivity) and are thought to live for approximately 100 years. There are at least 10 different species of giant tortoises in the Galapagos Islands, varying in size, shell shape, and geographic distribution.