Reptiles of the Galapagos Islands
There are many iconic creatures of the Galapagos Islands are reptiles. Certainly the Marine Iguana and the tortoises are among these island icons. Of course, there are also the boobies and the Waved Albatross and the energetic and good-tempered sea lions. But the slow moving reptiles are always well represented in the photographs of visitors. They pose and pose and pose.
Here we will take a look at the reptiles of the islands. It is little surprise that birds and reptiles make up a large part of the biomass of these remote islands. Birds arrived on the islands by chance because they could fly and reptiles arrived because their metabolism slows down and as they are occasional feeders were able to withstand the long (and fortuitous) journey by sea to the islands. There are four sorts of snakes on the islands, three species of iguana, six endemic species of geckos, and seven species of lava lizards. And, one species of tortoise in many guises. I will ignore the snakes and geckos for now; the following deals with iguanas, Lava Lizards, and tortoises.
The tortoises vary in appearance. The shells of those residing on islands where the vegetation has a tree-like form have a notch in the upper shell so they can extend their long necks upward. Those from lush(er) islands where vegetation is found rather easily at your feet have domed shells without a notch. Most herpetologists list 14 forms of tortoise in the Galapagos. Three forms are extinct and have been since they were gathered for food by pirates, buccaneers, whalers, and sealers back in the 18th and 19th centuries. Taxonomically there is only one species; with two major morphs (shapes: domed and saddle); with (originally) 14 varieties or forms. Each type is restricted to a specific island and a specific habitat on the island. Some islands do have more than one form, but each population is restricted to a specific bit of geography.
The domed shell is rather even throughout its circumference. The bearers of these shells have shorter necks and easier pickings than do the saddle-backed tortoises.
The saddle-backed tortoise shell allows for a longer neck to reach out and up to obtain food that is not at ground level. Much of the food these tortoise go after is a tree-like Opuntia cactus. The Spanish word for saddle is the base for the word Galapagos. Spanish saddles have a cantle board and look much like the tortoise shell shown in the image above.
|Male tortoise are much larger than females. Though they are usually silent and occasionally hiss, during mating the male can be heard at some distance.|
There are two types of iguana that visitors usually see; the ubiquitous Marine Iguana and the much less common land iguana. There is a third species, another land iguana, that is restricted to a very small home range and is not seen by visitors. The Land Iguana is a large, colorful, and hulking lizard where the marine iguana is smaller, darker, and very common.
During the times of feral cats, dogs, goats, burros, and rats the iguanas were decimated. Their eggs were dug and eaten, the young were also a regular food source, and there was little chance of hiding from the predation. During the past couple decades there have been exceptional efforts to remove cats, dogs, and goats from some (now many) of the islands. In many cases the eradication of invasive and alien species has been nearly completed. On the islands where this change has occurred the land iguanas are now able to hold their own and are beginning to repopulate.
On this last visit we saw one young Land Iguana, a first for many of the professional guides. Sadly, there was a feral cat seen within fifty yards of where this youngster was sunning.
Opuntia cactus is an important food plant where it is found. In addition to the tortoises and iguanas there are finches that eat the seeds, the flowers, and the fruit. In fact much of the pollination is carried out by cactus finches.
Land Iguanas are heavy-looking and rather colorful creatures. They burrow into the tuff hillsides and spend their day in pursuit of Opuntia cactus pads – spines and all. Like many animals in warm climates with long life spans they are not frenetic breeders and their recovery from the impact of feral domestic animals is a slow process.
The Marine Iguanas are much more common than the land iguanas. They are purely coastal creatures. They feed on marine algae, usually eating while underwater; though they will graze on the algae on rocks exposed at low tide. Their bodies cool significantly in the water and then spend a good deal of the day sunning, often in a pile of their brethren.
Though there are color and size differences between the various populations of Marine Iguana they are considered to be one species; though there are seven sub-species. They are able to isolate the salt from their diet and eject it in short, but rather violent, bursts from their nostrils. Males will compete with other males for dominance in an area by walking about and head-shaking. These action draw the attention of others and then displays the vigor of the displaying male.
Because the islands are so young and so volcanic there are few beaches of sand. On the older islands there are some sand beaches and on other islands there are beaches of crushed urchin spines, small pebbles, and other fragments. Thus, nesting sites for marine iguanas are few and far between. This lack of suitable nesting habitat seems to be the most limiting factor that they face. In a place without predators limitations are met and overcome by longevity, persistence, specialization, and of course (how Darwinian) evolution.
The last of the common and easily seen reptiles is the Lava Lizard. Compared to the tortoises and iguanas this small lizard is a bit of an after thought. It is a creature of the shrubby inlands though it occurs in vegetation right down to the shore. The males are mottled with a rough skin, a red throat, and a dorsal crest. An adult female will have smoother skin, be smaller than the male, and have a red or orange throat. The top image below is a male and the lower image is a female.
The male lava lizard is rougher in appearance than the female. Like most of the animals of the Galapagos populations are often specific to certain islands. In the case of the lava lizards there is one fairly widespread species and six other species that are island-specific.