Shedding light on Little Cayman’s iguanas

The Rock Iguanas of Little Cayman are the subject of a study this summer.

This summer, Little Cayman’s native iguanas are the stars of a research project being led by Jen Moss of Mississippi State University’s Department of Biological Sciences.

The team led by Ms. Moss, who is a Ph.D. student, is studying Little Cayman’s Sister Islands Rock Iguana population, which numbers between 1,200-1,500 mature individuals. Among other things, the researchers are examining the animals’ nesting habits and genetic makeup.

Dr. Glenn Gerber of the San Diego Zoo Institute for Conservation Research, and Matthias Goetz of the Durrell Wildlife Conservation Trust both spent time studying the iguanas in the early ‘90s and from 2007-11, respectively, inspiring the current research project.

“Thanks to their efforts, many details of these animals’ natural history and ecology came to light, including major sites where nesting occurs,” said Ms. Moss.

She said that renewed efforts to monitor trends and identify major threats to the animals arose recently when it was suspected the population was declining in the face of human development. Development has already reduced the Brac population to critical numbers, where it is thought there are not more than 100-200 adult iguanas left.

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Ms. Moss noted that because of these imminent conservation concerns, Cayman’s Department of Environment has been a strong supporter of Sister Islands Rock Iguana research.

“Outside of obvious human threats such as habitat loss, predators, and road traffic, my conservation questions are also focused on other aspects of long-term population maintenance,” said Ms. Moss.

“My Ph.D. advisor, Dr. Mark Welch, is a researcher of evolutionary and conservation genetics, and the chief focus of our lab in studying Caribbean populations is the unique evolutionary mechanisms that govern small, isolated populations. Little Cayman’s Sister Islands rock iguana population, which is still relatively robust and healthy but facing recent declines, offers an ideal system to investigate early symptoms of inbreeding depression and possible evolved mechanisms to combat it.”

She says the hope is her work, which is funded by the International Iguana Foundation and the Rufford Foundation, will help incorporate genetic health into the species action plan, and to better predict losses in genetic diversity, which could impact the animals’ numbers later on down the road.

Field assistant Mikey Kartje and researcher Jen Moss use a radio and antenna to locate one of the tagged iguanas.
Field assistant Mikey Kartje and researcher Jen Moss use a radio and antenna to locate one of the tagged iguanas.

Unique population

Ms. Moss said the Little Cayman iguanas make for a unique study subject group for evolutionary genetics because of their high level of isolation.

“Any island population is going to be isolated to a degree and be unique because of it, but the Sister Islands are especially interesting to evolutionary biologists because they are each less than 15 square miles in size and at least 60 miles from the next land mass.”

The Sister Islands rock iguana is officially listed as a subspecies of Cuban iguana, and it is thought to be closer on the evolutionary tree to Cuban iguanas (Cyclura nubila) than the Grand Cayman Blue Iguana (Cyclura lewisi).

“Even so, this ‘subspecies’ has a very restricted range compared to rock iguanas on other island chains or on very large islands, which means it has likely had to had to evolve some traits to make it resilient to extinction,” said Ms. Moss.

“It is also important to note just how pristine Little Cayman is. Cayman Brac, only slightly larger, is comparatively much more developed, and its natural populations have dwindled as a result,” she continued.

“I am awestruck every time I fly over Little Cayman by just how much of the tiny landmass is untouched, wild forest. I think that makes these iguanas a little special. While the residents of Blossom Village’s museum barely flinch at the approaching human anymore, the true “bush” iguanas and the East Enders impart a special kind of wildness when you see them. It is really amazing to me to think that on an island as small as Little Cayman, there are still wild lizards running around that have never encountered a human.”

Tracking nesters

To track their subjects, the team is marking adult and hatchling iguanas with transponder (PIT) tags, similar to a microchip for a dog or cat, “This allows us to scan an animal’s tail and immediately identify it by its unique serial number,” said Ms. Moss.

The team is also marking the iguanas with a unique combination of colored glass beads. These are threaded with a fishing line through the crest spines, similar to an ear piercing, and makes them easy to identify by sight.

Field assistants Mikey Kartje and Tanja Laaser extract an egg during a nest excavation.
Field assistants Mikey Kartje and Tanja Laaser extract an egg during a nest excavation.

“Marking animals is extremely useful for the study of individual movements, behaviors, and growth,” she said.

The nesting surveys are being done along the coastal West End of Little Cayman, where most of the island’s iguanas live. The habitat has deep, sandy soils ideal for digging nests, and sparse shade vegetation like palms and shrubs.

“Since they are underground, iguana nests can be very tricky to identify once they have been sealed,” said Ms. Moss. “We visit our sites at least twice daily to note any disturbances to the soil or, if we are lucky, catch an iguana in the act of digging.”

Once a nest has been closed and the guarding period, which can be up to four weeks, has ended, the researchers carefully excavate it to locate the egg chamber and take egg counts.

Ms. Moss said by chance researchers noticed that some females at communal nest sites are taking advantage of the digging efforts of other iguanas by reusing already dug nesting burrows.

“I am hoping to learn more about this kind of behavior, including how often it occurs and what kind of effects it has on the original nests,” said Ms. Moss.

The researchers are tracking iguanas with radio transmitters, both on foot and by using drones. It seems that many females choose the same nest sites year after year, traveling sometimes long distances to sites which are not necessarily close to, or most easily accessed from, their home territory.

“This lends support to the idea that site selection by females may be more governed by behavioral ecology than by habitat suitability or proximity,” said Ms. Moss.

“It also underscores the fact that nesting season is a particularly dangerous time for nesting females, as many of them are coming from deep in the interior of the island where they never encounter humans and spending a disproportionate amount of time crossing roads.”

A memorable experience

Ms. Moss says that conducting the research on Little Cayman since May has been a truly enjoyable experience.

“I love working on Little Cayman. When I first started everyone was wishing me ‘Good luck,’ warning me about the heat and how it was going to be so utterly boring there that it would drive me insane,” she laughed.

“But beyond the price of vegetables, I wouldn’t have it any other way. People are so incredibly friendly – in a way that friendliness only evolves when there are fewer than 200 people and the speed limit across the whole island is 25 miles per hour. The pace of life is so relaxed and ‘hakuna matata,’ which relieves the what would otherwise be maddeningly hectic pace of fieldwork,” she said.

That being said, she conceded that iguana chasing is tough work.

“I would not recommend any recreational bushwhacking or lizard wrangling, as they are very wild animals with very sharp teeth, and eight-nine hour days in the Little Cayman heat are not without their delirious moments,” she said.

“However, if you are able to acclimate to some sweat and discomfort, it becomes much easier to appreciate the natural beauty of the place.”

Ms. Moss plans to return to Little Cayman for the month of August when the hatchlings will be emerging. The researchers will return to the nests they marked in May and June to sample and tag hatchlings for some of the project’s ongoing studies of growth and dispersal.

Ms. Moss says she is also hoping to examine whole clutches to assess genetic diversity and determine parentage, and next year, the hope is to track hatchlings to see where they go, which will provide insight on gene flow, as well as on mortality rates and the ideal habitat characteristics for survival.

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  1. Huge kudos to Little Cayman resident Mikey Valley for keeping the Little Cayman Iguana research program alive among the local residents. Mike and Ed do tremendous work keeping the Green Iguana’s (Iguana Be Gonna initiative) from getting established on Little Cayman, and monitoring and protecting our local Rock Iguana population. Thanks to you both for you work.