Mammals dominate life in many parts of the planet, but on the Galapagos, reptiles rein largely due to the hot, dry climate that suits their needs. The Galapagos supports 25 native species of reptile (19 endemic) and early on Charles Darwin labeled the islands a “paradise” for reptiles, cold-blooded creatures with slow metabolisms that don’t necessitate a large supply of food and skin that offers sun protection. Without many mammals on the islands, reptiles on the archipelago encounter negligible amounts of predation and competition, making them easier for those traveling to the Galapagos to see and enjoy at very close range.
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Pacific Green Sea Turtle | Marine Iguana | Land Iguana | Lava Lizard | Giant Tortoise
PACIFIC GREEN SEA TURTLE
The Pacific green sea turtle breeds and lays eggs in the Galapagos, but it is not endemic to the islands. They are called “green” because of the color of their flesh, and are one of the largest of the turtle species, ranging from 2.5 to 5 feet in length and weighing up to 450 pounds.
These turtles have paddle-like limbs, the shape of which aids them in becoming proficient swimmers. The carapace of the green sea turtle can be olive to brown, or sometimes even black, depending on the geographic location of the species. Males are larger than females and have longer tails, which extend well beyond their shell.
Green sea turtles cannot pull their heads and limbs inside of their shells, which makes them more vulnerable to predators. They are mostly herbivorous and they spend most of their time feeding on algae in the sea and on the grasses that grow in shallow waters. As juveniles, they eat plants and other organisms such as jellyfish, crabs, sponges, snails and worms. As adults, they are strictly vegetarians.
Green sea turtles are quite promiscuous during the breeding season, especially between November and January, when mating activity can often be observed in the water. Nesting occurs at night on many of the sandy beaches of the islands mainly from December to June, peaking in February. The female digs a hole in the sand above the high tide mark and deposits several dozen eggs, a process which takes about 3 hours. She then covers them with sand to protect them from the sun, heat and predators and returns to the ocean.
The newly laid eggs incubate in the sand for 50 to 60 days. The temperature of the nest determines the sex of the turtles, with cooler nests producing a clutch of males, and subsequently, warmer nests producing more females. On a clear, moonlit night, the hatchlings will dig themselves out of their nests and scramble towards the water. Once away from the protection of their shells, they are extremely vulnerable to predation. Only 2 inches long, the tiny, helpless turtles have a treacherous journey, struggling to avoid ghost crabs, sea birds and fish on their way to the open sea. Once they reach their destination, the turtles swim away for years. Almost nothing is known about this period of their lives, until they again return to nest at the same beach in which they were born.
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The marine iguana is the only sea-going lizard in the world and is found on the rocky shores of most of the islands. This iguana has a blackish skin, which in males can change to startling blues and reds during the breeding season. Breeding occurs at different times on different islands; the males on Española are colorful year-round. Marine iguanas are colonial, often seen piling atop one another, but when breeding, the larger males become territorial and aggressive, butting and pushing their rivals. Mated females lay two to four eggs in a sandy nest that they guard fiercely, although the hatchlings, which emerge after 3 or 4 months, are not given much parental protection.
Marine iguanas feed mainly on intertidal seaweed, although mature males have been recorded offshore at depths up to 40 feet and submerged for over an hour. The row of spines along the entire length of their backs, their scaly skins, their habit of occasionally snorting little clouds of salt spray into the air, and their length, which can reach almost 3.3 feet, make them look like veritable little dragons.
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Both land iguanas found in the Galapagos look almost identical; these two species are yellowish in color and bigger than their marine relatives; adults weighing as much as 13.25 pounds have been recorded. The Galapagos land iguana lives on South Plaza, Isabela, Santa Cruz, Fernandina and Seymour Islands, with South Plaza offering the best viewing opportunities. Previously, they inhabited a majority of the archipelago, but hunting and competition from non-native species such as goats, rats, pigs and dogs, which prey on iguana eggs, led to their demise on many islands. The similar looking Santa Fe land iguana, limited to Santa Fe Island only, is, on average, slightly bigger and more yellow than the Galapagos land iguana and has more pronounced spines. They can exceed 3.3 feet in length.
Both land iguana species choose prickly pear cactus as their preferred food, often needing to stand on their back legs to feed on the yellow blooms and juicy cactus pads, which they can eat whole and with spines intact due to the fact that iguanas have leathery mouths.
Land iguanas are known to live for at least 60 years. They reach sexual maturity between 6 and 10 years of age. Mated females lay between five and fifteen eggs, and like the marine iguana, they defend their nests until hatching occurs. The breeding season for land iguanas occurs during different months on different islands.
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Less spectacular than the iguanas are the seven species of lava lizards, which are frequently seen scurrying around. They can reach up to 1 foot in length, but are usually smaller. Their most distinctive behavioral patterns are rapid head bobbing and push-up stances, which are performed in order to defend their territories and to assert dominance.
The male is larger than the female and is strongly patterned with yellow, black and brown coloring. The female’s design is less intricate, but instead, stands out with her flaming red throat. It is easy to separate the seven species of lava lizard by geographical distribution. Six of the islands have their own endemic species that are found nowhere else in the world.
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Of all the wildlife in existence today, the giant tortoise best symbolizes the Galapagos Islands. In fact, the word Galapagos is Spanish for “shape of a saddle,” which is what many tortoise shells actually resemble. Fourteen subspecies, each in some way distinctive to the island of its residence, comprise the sole giant tortoise species. Of these fourteen varieties, three are extinct. One of the best ways to distinguish those still in existence, apart from geographic distribution, is by the differences in the shape of their shells. These differences, as described in The Voyage of the Beagle, contributed to the development of Darwin’s theory of evolution:
“I have not, as yet, noticed by far the most remarkable feature in the natural history of this archipelago; it is, that the different islands, to a considerable extent, are inhabited by a different set of beings…I never dreamed that islands, about 50 or 60 miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a nearly equal height, would have been differently tenanted; but we shall soon see that this is the case. It is the fate of most voyagers, no sooner to discover what is most interesting in any locality, than they are hurried from it; but I ought, perhaps, to be thankful that I obtained sufficient materials to establish this most remarkable fact in the distribution of organic beings.”
There are two major shell designs of the giant tortoise. The upper half of the shell, called the carapace, is distinct from the plastron, or lower half. The “dome-shaped” carapace is found on larger varieties of tortoise from Santa Cruz and the Alcedo Volcano on Isabela, where the large tortoises feed on the relatively lush vegetation. The “saddleback” carapace, found on the Hood (Española) and Pinta varieties, allows for the tortoise’s long neck to emerge, permitting it to feed on the hard-to-reach vegetation of the drier islands.
Tortoises are vegetarians and their diet includes grasses, forbs and leaves on bushes. They have been known to eat several peculiar foods such as stinging nettles and crab apple-like fruits of the manzanillo tree, which burn human skin. They also have very slow digestive systems; it can take their bodies up to 3 weeks to fully process a meal. Scientists guess that the tortoise’s life span is somewhere around 150 years.
The giant tortoise reaches sexual maturity at about 40 years of age. Between the months of January and August, towards the end of the rainy season, the male begins sniffing the air for a female’s scent. He will posture and heave competitive males to demonstrate his dominance, and then begin the search for a female mate. Once a female is found, he chases her down and begins his style of courtship with intimidation. He rams her with the front of his shell and nips at her exposed legs until she draws them in, immobilizing her. He then mates with her. Males unsuccessful in finding a female partner have been known to attempt to mate with other males, or even with appropriately shaped boulders!
Having mated, the female looks for a dry, sandy area in which to make a nest. Starting a process that takes up to several days, she uses her hind legs to dig a hole approximately one foot deep. Between two and sixteen eggs are laid and are then covered with a protective layer of mud made from a mixture of soil and urine. The eggs take about 4 to 5 months to develop, and hatchlings usually emerge between December and April. When the eggs hatch, the baby tortoises are forced to fend for themselves, most dying within the first 10 years of life.
Known for their ability to go without eating for extended amounts of time, the tortoises voyaged to the islands aboard rafts of vegetation. They have tremendous water storage capacities, which enable them to survive the long, arid season. This special attribute became a curse when buccaneers and whalers, keenly aware that the animals could withstand long voyages up to a year without food or water, harvested them by the thousands for their meat. They were stored upside-down in the bilge, ready for slaughter when fresh meat was on the menu. As a result of their endemic capture, only 15,000 remain today.
Presently, at the Charles Darwin Research Station, a tortoise-breeding project has achieved successful results and increased the depleted population by introducing these animals into the wild. The research station provides us with the easiest and most convenient facility in which to view both tiny yearlings and full-grown adults. Although the tortoises are in enclosures, visitors are permitted to enter to get a closer look at these giants, some of which can reach up to 550 pounds and could quite easily carry a full grown man on their back. Adults weigh over 1,000 times more than newborn hatchlings, which weigh-in at less than half a pound.
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