Preserving Wildlife

Caribbean Rock Iguana Recovery Programs

Sometimes in a crisis you have to make tough decisions. In iguana conservation, this can mean interfering in an animal’s normal life for the benefit of the future population.

When I arrived in Grand Cayman to assist with the Blue Iguana Recovery Program a few years ago, a large wild female iguana had just been spotted in abandoned pasture at the far end of the island. It was the time of year when females are looking for the right spot to lay their eggs and she had been seen digging a few test holes. We had a rough estimate that only 25 iguanas remained here, so finding her was big news! We needed to locate her and see if she really was going to nest.

When a population becomes critically rare, some conservation methods are aimed at boosting the number of animals as quickly as possible first, and later refining the strategies to keep them safe. 

For the recovery of four critically endangered Caribbean iguana species (Grand Cayman Blue, Jamaican, Anegada, and Mona), we have been collecting hatchlings when they emerge from the nest and raising them in specially built facilities on their respective islands where they are safe. These “headstarted” iguanas are released back to the wild once they have grown large enough to defend themselves against the non-native predators such as cats and mongooses that have invaded their island homes.

This strategy is demonstrating measurable success at increasing the populations, despite the challenges they face.

The Grand Cayman program also manages a breeding center with adult iguanas that represent all the known genetic diversity of the remaining wild population. Since we believed this “new” female (nicknamed Maria) was unrelated to the animals already in the program, our hope was to collect her eggs so that we could breed her offspring in future years and maximize the numbers in this family line.

We also planned to radio track Maria so she could lead us to the location of her wild mates.

After a reconnaissance to the site where she had been seen, we decided the area she was most likely to look for a nest site was too large to watch from a blind.  However, there was a large spindly tree at the edge of the clearing that had a great view of the area.  Being the smallest and most monkey-like researcher in the group, I volunteered for observation duty. 

The few iguanas still surviving on the island have learned to be extremely wary of people on the ground, but we hoped they would be unperturbed by a biologist sitting in a tree!  I spent the next four days in the mango tree looking for Maria.

On the first morning, I saw Maria emerge from a burrow under a large rock. She wandered around the clearing briefly and scratched the dirt in a few places before ambling off into the thick forest.  I could tell from her swollen sides that she was gravid.  Iguanas need to nest in open, sunny patches so I knew she wouldn’t nest in the forest. Every day I watched her emerge in the morning from the same burrow, and not return until dusk. I did not see any nest building. 

On the fourth day, I climbed the tree a little later than usual and didn’t see her by her burrow.  A few hours later I spotted her eating a shrub across the clearing and her sides were totally sunken in.  What?!  She had laid her eggs somewhere and I missed seeing where!  I could only start looking in the areas where I had seen her scratching and cross my fingers.

I called another team member for help and we spent several hours digging around the clearing. Finally, I found an old eggshell and knew that an iguana had chosen that spot in the past. Sure enough, after 45 minutes of carefully excavating the area, we found a cluster of eggs. 

Our elation at finding the nest quickly turned to sadness when we realized the eggs were not tight and perfectly ovoid as they should be, but deflated, indicating they were all infertile.  Iguanas have very keen senses and if there were mature males anywhere near the area they would have found Maria.

This clutch of infertile eggs meant there were no other iguanas around and Maria was the lone survivor in the area.

As much as we wanted to leave Maria in her wild home, we knew she had no chance of producing wild offspring in the near future—our plan to have this year’s offspring join the breeding program was not going to happen. We would have to capture her instead and start choosing mates for her and hope she liked them! 

We are working toward a goal of a restored wild population, where all iguanas live free.  Maria was certainly grumpy about our decision. But, for the benefit of future generations, she will need to live in a home that is safer and has more chance of reproduction, but without a mango tree at its edge.

Tandora Grant, Applied Animal Ecology