Not Just Another Iguana

Story & Photos by Ahrash N. Bissell,
Dept. of Biology, University of Oregon

A typical day in paradise: about 30 degrees Celsius, sunny but a bit hazy, with a moderate wind coming out of the east. Long stretches of white sand extend in either direction, and the few groups of people are alternately lazing on the beach or relaxing in the clear blue water. My field assistant, Kit Lacy, and I wade into the ocean with a small boat in tow; when the water is deep enough to unprop the motor, we hop in, start the engine, and head out into the Atlantic. We don’t have far to go, and in a few minutes we have landed on an uninhabited island nearby.

After pulling up the boat, we turn around and find ourselves surrounded by large lizards. And there appear to be even more of the reptiles coming out of the bushes to check us out. They are all different sizes, with the largest being about two feet long; they are blue-green, have long tails, and look at us with eyes that can be forest green or coppery-red or somewhere in between. Some of them have enormous spines running from the head all the way along their backs and down their tails. They chase each other around, jockeying for position in case one of us has something for them to eat. They look like throwbacks from the earliest days of the dinosaurs, except that here they are, alive and basking in the tropical sun.

The place is the Turks & Caicos Islands. “Where?” is a typical response when I tell people where I’m going. The Islands seem mysterious and remote to most people, which is of course part of the attraction to the place. But the remoteness has contributed to the Islands in other ways as well.

The Turks & Caicos have a similar geological history to the Bahamas, but are otherwise quite distinct, historically and biologically. Deep oceanic trenches surround the Turks & Caicos; therefore, all of the plants and animals that exist there must have arrived by air or water. Once these organisms got to the Islands, many of them evolved into unique forms and are consequently found nowhere else on earth. The Turks & Caicos Rock Iguana (TCI Iguana) is a good example of this phenomenon. With the exception of a separate subspecies on Mayaguana Island in the Bahamas, this iguana can only be found on a few islands and cays in the Turks & Caicos.

Kit and I make our way over to the boardwalks that were built on Little Water Cay in order to protect the iguanas and to facilitate tourism to the area. It is obvious that the iguanas are fed regularly: they are extremely bold, often climbing up onto the boardwalk and investigating our toes to make sure they arenÕt some sort of new fruit. The density of iguanas here is amazing; the TCI Iguana naturally occurs in some of the highest densities known for any iguana species, and the concentration of iguanas around the boardwalk is probably even higher than normal. These iguanas have obviously learned that humans have tasty food; therefore, they stick around the boardwalks. They seem to learn many things quickly, which is also unusual for most lizard species.

Kit and I set the video camera and begin to record the displays and other behavioral traits of the iguanas. Social behavior is just one of many different areas of research on the TCI Iguana that I am working on for my thesis work. The focus of my interests tends to change on a weekly basis (much to the exasperation of my graduate advisors), but in general, I am interested in the interaction of different species with their environments, and how important these interactions are in the evolution and conservation of those species.

The fields of ecology and evolution offer many theories and ideas to explain much about the biology of any organism, but general theories only go so far. Each organism has its own unique natural history, and those features that make an organism what it is cannot be subdivided and generalized without losing the essence of the organism.

These days, there is much talk about preserving biodiversity. The concept of biodiversity is somewhat nebulous, but ultimately the idea is rooted in the fact that biological species cannot be recreated or replaced. To call the TCI Iguana an “iguana” is like calling a human being an “ape”. Technically, the label is correct, but biologically, each iguana species is as different from each other as a human is from a gorilla. To appreciate those differences, and to begin to get a sense of why those differences exist, one has to study each species in detail.

My thesis advisor, Dr. Emilia Martins, is particularly interested in lizard communication, and she is beginning to gather details about the complex and fascinating displays given by the TCI Iguana. In addition to behavioral research, I am hoping to gather details about the environments in which the iguanas live, the effects of human visitation to the Islands, the health of the iguanas, and a variety of other biological measurements. Hopefully these data will help to show both scientists and the public how unique the TCI Iguana is, and how in need of more research and protection they are. Although studies on the TCI Iguana have been few and far between thus far, we already know quite a few interesting details about these unusual reptiles.

The bulk of what we know about the natural history of the TCI Rock Iguana is due to a long-term study by John Iverson, who is now a professor at Earlham College in the United States. He performed his study in the mid-1970s as a graduate student; since then, not much has been done by anyone.

One thing we do know is that the TCI Rock Iguana is long-lived; in fact, the females probably don’t begin reproducing until they are 6-7 years old, and they probably live to be 15 years or so. Once females reach reproductive maturity, they lay 2-9 eggs per year in burrows dug out specifically for this purpose. The females seem to then defend the burrows for a period of time, but they abandon the site before the eggs hatch. Even though the lizards live for a long time and the females lay many eggs each year, John Iverson found that the iguana populations seemed to be just replacing themselves. In other words, there were as many iguanas surviving to maturity as there were dying each year.

In the past, when the iguanas were the only large land animals on the Islands, it would have been beneficial for the iguanas to keep the populations at a steady level, since a growing population would probably quickly strip the tiny islands of all their food. However, now that the iguanas are suffering from predation and habitat loss, they would benefit from being able to produce more offspring and having more of those offspring reach reproductive age. All of the factors that limit iguana population sizes aren’t known, so it is difficult to say how easy it would be for a small iguana population to grow into a larger, more stable one. This problem is yet another example of an area of research specific to the TCI Rock Iguana which would greatly aid our efforts to understand and protect the remaining lizards.

Some other interesting traits of the TCI Rock Iguana include the fact that the mating season is timed with the rainy season. Although it rarely rains much in the Turks & Caicos (although some residents of North Caicos may beg to differ), the slightly greater quantity of rainfall that begins in the early summer is enough to trigger new growth in many plants, which the iguanas can then eat.

The mating season may also be timed with the increased heat of the summer. Iguanas, like all reptiles, are ectotherms (or cold-blooded), which means that they have to regulate their body temperatures according to the temperatures available in their environments. On a hot day, the iguanas can warm up quickly and actively forage. The increased body heat allows them to digest their food more efficiently as well. And if it gets too hot, they can always retreat into their burrows. On the other hand, it may be difficult for the iguanas to warm up on a cool or cloudy day, in which case they may not even bother to emerge from their burrows to eat or interact. I found that many of the iguanas would climb to the top of the bushes in the morning in order to catch the sun as early as possible. Obviously, temperature-regulation plays a big role in these iguanas’ lives, even in a perpetually warm environment like the Turks & Caicos.

The iguanas seem to eat a lot of different plants and plant-parts. Not surprisingly, they seem to eat most of the fruits that appear on different plants throughout the season. The bulk of their diet is probably leaves, however, and they definitely have preferences. During the course of my studies, I saw them eat the leaves of Seven-year Apples, Sea Grapes, Sandfly Bushes, and young Silver Palm fronds, among other species

Interestingly, different iguanas seem to prefer different plants, although I haven’t been able to study those differences in any detail. Also, different plants are likely to vary quite a bit in their nutritional benefits to the iguanas. Therefore, if the number and variety of plants on an island are low, then the iguanas may not obtain enough nutrition to stay healthy. As more and more habitat is developed and the iguanas are left on smaller and smaller islands, this problem will probably become more serious.

Each spring, in time with the onset of the mating season, the iguanas go through a period where display intensity increases, especially when males approach females with a courtship display. As far as we know, females mate only once, but how the female chooses a particular male is a mystery. In fact, it’s not at all clear that females actually have the option to choose a mate; the males are considerably larger, so it may be that the largest males simply overpower the smaller males and then the females as well. However, the communication between these lizards is complex, and we believe that there may be displays for submission, rejection, acceptance, and a whole host of other possible outcomes. This behavioral complexity, while fascinating, makes it difficult to study the social structure and language of this species.

Rock iguanas are social animals, unlike most lizards which tend to shun others of their own kind. That’s not to say that they all get along; on the contrary, fights break out constantly, especially among the larger males. Most mature iguanas are missing one or more toes from these battles, and we have handled and observed some iguanas that are missing a foot here, the whole tail there.

Obviously, these fights are dangerous and costly to the iguanas, but despite the fact that fights are rather common, we still don’t know what they are fighting for. There are many theories as to why animals fight. A common idea is that males must battle each other in order to impress females, who then choose the victorious males as their mates. For the TCI’s iguana, this theory may be correct, but so little is known about the reproductive success of different individuals that we can’t even be sure that there is any female choice at all.

Another idea is that each lizard defends its own territory, perhaps in order to protect certain food sources, or burrow sites, or especially good basking sites. Again, this theory could apply to the TCI iguana, but much more work is needed before we will be able to tell if there are differences between home ranges, and whether those differences are defendable.

Regardless of what they are fighting for, it is obvious that the best option for the iguanas would be to avoid fighting altogether. Indeed, most encounters between iguanas don’t result in a fight; instead, the individuals display at each other. In essence, they are “talking things over”. In this way, they can communicate who they are, how strong they are, and what they intend to do. If the interests of the two iguanas don’t conflict, then they will probably ignore each other.

Typically, when two adult males encounter each other, they approach each other and perform a display, utilizing a series of rapid up-and-down motions with the head, termed “head-bobs”. The structure of this display varies considerably between individuals, which is why we believe that they may be able to communicate their individual identities to the other iguanas.

Interestingly, it also looks like different populations of the TCI Iguana (on different islands) have different ways of communicating. This phenomenon is akin to dialects around the United States, or perhaps even of slightly different languages. We can’t tell how important the differences in communication are without further study. Around the boardwalks on Little Water Cay, the iguanas display at each other all the time, probably as result of arguing over who gets the tourist handouts.

The issue of how the presence of people affects the iguanas is not trivial. The Turks & Caicos Islands, and Providenciales in particular, are rapidly becoming a major tourist destination for Caribbean travelers. Anyone who has been living on Provo during the last five years can tell you how much it has changed. Given the current rate of construction and the rapid increase in tourist traffic, there will undoubtedly be many more changes in the near future. These changes have brought economic prosperity to the Islands, and the current rate of growth, coupled with the political stability of the country, have spawned a major off-shore investment industry. For most people in the Turks & Caicos, these changes have led to a growth in their income, and the future looks bright.

The rapid growth and economic prosperity currently seen around the Turks & Caicos are the result of the country’s major asset: its nearly pristine waters and abundant wildlife. The country is blessed with beautiful beaches and warm waters, and it is still possible to easily reach isolated stretches of sand, or even entire islands, for the ultimate experience of tropical solitude. However, warm weather, clear water and long beaches aren’t unique to the Turks & Caicos, and in these days of the increasingly budget-conscious traveler, those people who are only interested in a good swim and a full-body tan are likely to be satisfied with a far more accessible location. Therefore, it is those assets that are more unique to the Turks & Caicos that keep visitors coming back, and bringing their friends with them.

During many different conversations with tourists from around the world, there were three features of the Turks & Caicos that were brought up again and again as the primary attractions to the country. The coral reefs and incredible sea life obviously top the list. The Turks & Caicos are considered by many to have the best diving and snorkeling in the region, which is remarkable considering the vast number of alternative locations throughout the Caribbean. The second attraction is the ease with which people can escape the crowds and visit isolated islands and beaches. On Provo, this endeavor is particularly simple because of the protected and uninhabited cays between Provo and North Caicos. The third major attraction is the Turks & Caicos Rock Iguana, which attracts thousands of visitors to Little Water Cay every year.

The TCI Iguana represents practically the only land-based ecotourist opportunity on the Islands; as such, these friendly reptiles have amazed and delighted tourists by their relative abundance on Little Water Cay and their surprisingly prehistoric demeanor. Coupled with the well-made boardwalks and signs on either side of Little Water Cay, the TCI Iguanas have become a significant tourist attraction.

I am drawn to the TCI Iguana for several reasons. The primary reason is the unique nature of the reptiles. Besides being an interesting organism, the iguanas are an excellent species with which to study general biological processes which pertain to most life on earth. A second reason I work with the TCI Iguana is that the species is in desperate need of conservation action. It is an internationally endangered species; as such it is protected by the Convention on International Trade of Endangered Species (CITES) and is recognized by the World Conservation Union (IUCN) as a species in need of further study and protection.

The iguana used to number in the millions, and is the largest native land animal in the entire country. Habitat destruction and degradation, coupled with predation by feral dogs and cats, have decimated the TCI Iguana’s populations. Today, with a few notable exceptions, you can only find the iguana on isolated islands that are not and never have been inhabited by humans.

Basically, the iguana will probably persist indefinitely if it is given enough space and protection from human pets. However, the iguana’s need for space is in direct conflict with the current program of rapid development that is changing the face of the Turks & Caicos Islands today. These conflicting pressures have brought the TCI Iguana to the forefront of conservation efforts in the country and have garnered international attention. The plight of the iguana, like that of so many species, is the reason that the iguana is considered special to most people who have seen or heard of it.

However, an organism doesn’t have to be rare or endangered to be interesting. And, as shown here, the TCI Iguana is a particularly fascinating reptile in its own right. Hopefully everyone who visits the Turks & Caicos will take an hour or two to visit these reptiles at their home on Little Water Cay.

Sit for a while on the boardwalks, or watch them from the observation tower. Note how they react to each other and to the tourists that walk by. Watch their displays and the way they move. Try to get a feel for the way they live, and try to imagine the changes these iguanas are experiencing after having been the only animals of their size on these Islands for thousands of years. Hopefully increased awareness of the iguanas will help to instill a greater appreciation for this national treasure as one of a few organisms that is entirely unique to the Turks & Caicos Islands.

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