Reptiles

The predominance of reptiles is one of the most striking things about the wildlife of the Galapagos Islands. Mammals, after all, tend to be the dominant large terrestrial life form in almost every other part of the world. The hot and dry conditions found throughout the islands for much of the year provide ideal habitat for reptiles to thrive. In fact, Charles Darwin described the Galapagos as a “paradise” for these slow moving, cold-blooded species. Because of their sluggish metabolisms, reptiles don’t require a lot of food, which means they are well suited to survive the seasonal and climactic fluctuations common to the islands. And the scarcity of mammals, which had a much harder time getting here from the mainland, means that Galapagos reptiles face far less predation and competition than reptiles in other parts of the world. There are twenty-five native reptile species in the Galapagos (nineteen endemic), and some, such as the marine iguana, are found in truly prolific numbers.

MEET THE REPTILES OF THE GALAPAGOS

Giant Tortoises
The giant tortoise is perhaps the most emblematic species of the Galapagos. In fact, the name Galapagos itself comes from the Old Spanish word for ‘saddle,’ in reference to the shape of some giant tortoise species’ shells. Today, the giant tortoise (and one individual dubbed ‘Lonesome George’ in particular) has come to symbolize both the uniqueness and fragility of life in the Galapagos.

Giant tortoises roamed throughout much of the world prior to the arrival of homo sapiens. Today, they are only found in a few isolated island groups in the tropics, including the Galapagos archipelago, the Seychelles and the Mascarenes. In the Galapagos they can weigh up to 550 pounds and are often cited as a text book example of island gigantism, a biological phenomenon in which the size of animals isolated on an island increases dramatically in comparison to their mainland relatives.

Scientists believe that the ancestors of today’s Galapagos tortoises drifted to the islands two to three million years ago from mainland South America. Eventually, fourteen separate populations were established on ten of the largest islands. Today, taxonomists consider each island population a separate species, though recent genetic studies suggest that there may be considerable differences between populations found on the same island.

Tortoises are now extinct on four of the islands where they were once found. Tortoises on Fernandina became extinct due to volcanic activity. Tortoises on Floreana, Santa Fe and Pinta disappeared because of human impact. The last known Pinta tortoise, affectionately dubbed “Lonesome George,” died in captivity in 2012.

One of the tortoises’ most amazing adaptations, the ability to survive without food or water for up to year, helped to speed their demise. Pirates and whalers in the eighteenth century discovered that tortoises were an excellent source of fresh meat as they could be stored alive in the hull of their ships for long periods of time.

Invasive species have also plagued the giant tortoise. Rats, pigs and ants devour eggs and hatchlings, while goats destroy tortoise habitat and compete with them for food.

It is believed that 100,000 to 200,000 tortoises were killed for food and their oil over the course of two centuries. Today, scientists estimate that there are around 20,000 to 25,000 wild tortoises left in the Galapagos. Successful captive breeding and reintroduction programs, along with massive efforts to eliminate goats and other invasive species, have helped bring ten of the eleven endangered giant tortoise species back from the brink of extinction. One particularly important initiative has repatriated over 1,000 young tortoises to the island of Española – the products of a successful breeding program involving the last thirteen remaining individuals of the species!

Giant tortoises generally reach sexual maturity at about twenty to twenty-five years of age. The mating season typically takes place in March and April. Pregnant females dig nests in sand and deposit their eggs from June to December. If all goes well, they will hatch in four to five months. Most of the hatchlings won’t make it past the age of 10. But if an individual does survive into adulthood, it may live to be 150 years old.

The Charles Darwin Research Station on Santa Cruz Island and the Tortoise Reserve in the Santa Cruz Highlands are the best places to see giant tortoises. Wild tortoises are most likely to be seen on San Cristóbal, Santa Cruz, and around Alcedo Volcano on Isabella.

Watch this video of two Galapagos tortoises showing a typical display of dominance, narrated by WWF:

Marine Iguanas
The marine iguana is another iconic Galapagos species. This endemic reptile is the world’s only seagoing lizard and can be found on rocky shores throughout most of the archipelago. A truly remarkable creature, the marine iguana has adapted to venture into the sea for food, a unique habit that gives it access to an abundant source of food year round. Its diet consists of algae growing on rocks, seaweed and even small crustaceans. Large males have been observed diving to depths of forty feet and staying under water for up to an hour. In such instances, the iguana’s body temperature may drop by as much as twenty degrees Fahrenheit.

Among the many adaptations that allow the marine iguana to occupy this unique ecological niche is a short, blunt nose (perfect for harvesting algae off of rocks), a long (half their body length), flattened tail that propels them effortlessly through the water, and a special gland that allows them to rid their bodies of the excess salt that they consume as part of their diets. Perhaps its most remarkable adaptation, unique among all vertebrates in the animal kingdom, is the ability to actually shorten its body length during lean times, such as famines caused by El Nino events. When food becomes plentiful again, the marine iguana will return back to its normal size. Researchers believe that in order to accomplish this miraculous feat of survival marine iguanas literally absorb a portion of their bones.

It is believed that there are seven subspecies of marine iguanas, which vary in size and color from island to island. Generally, they have blackish skin, which enables them to blend in with the ubiquitous lava rock that rings much of the islands.   During mating season, males turn red or reddish green. A spiny crest runs from their heads to the their tails, giving them a dragon-like appearance, especially when they “sneeze” excess salt into air.

It is estimated that the total population of marine iguanas is between 200,000 and 300,000, with concentrations of up to 4,500 individuals per square mile in some areas. While their numbers are healthy, the introduction of cats to the islands has had an impact on certain populations. El Niño events can also have a devastating impact on marine iguana populations. It is believed that 70% of some populations died off during the cataclysmic El Niño that occurred in 1982 and 1983. If young iguanas can survive the onslaught of avian predators, such as Galapagos hawks and herons, they may live to be 25 to 30 years old.

You are likely to see a lot of marine iguanas on your Galapagos trip, especially on Española, Fernandina, Genovesa, Isabela, San Cristóbal, Santa Cruz, Santa Fé, Santiago, Seymour, and South Plaza Islands.

Land Iguanas
There are three species of land iguana in the Galapagos Islands. Conolophus subcristatus is native to six islands, while Conolophus pallidus is found only on Santa Fe. Both are yellowish in color, though the Santa Fe iguanas are more whitish and often have dark brown patches.   The third species, Conolophus marthae is a pinkish color (thus often referred to as the “pink” or “Rosado iguana”) and is found only on Wolf Volcano on Isabela Island.

It is estimated that between five thousand and ten thousand land iguanas live in the Galapagos today. Conolophus subcristatus once existed on most of the islands in the archipelago, but now is only found on Fernandina, Isabela, Santa Cruz, Seymour, and South Plaza. Human hunting, predation by dogs and competition with introduced animals such as goats and pigs, have caused its numbers to decline. In 1975, two populations on different islands (Cerro Cartago on Isabela and Conway Bay on Santa Cruz) were decimated in less than six months by feral dog packs. Captive breeding programs and elimination of feral dogs have helped restore their numbers.

Land iguanas can grow more than three feet long and weigh more than 30 pounds. They live in some of the drier parts of the islands and feed primarily on low-growing plants and shrubs, native fruits and cacti. Because there is little fresh water in these areas, land iguanas get all of their moisture from the food they eat during long dry periods. One of their favorite foods is the prickly pear cactus. Their leathery mouths enable them to eat the cactus pads whole, spines and all.

Land iguanas live in small colonies and dig shallow tunnels for shelter at night. They reach sexual maturity between six to ten years of age. They mate at the end of the year and lay eggs from January to March. Females lay between seven and twenty-three eggs and will defend the nests for three or four months until the eggs hatch.

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