Conserving the Cayman Islands iconic 'blue dinosaurs'

“I’m frothing for blue iguana ‘til I die!” – it’s the kind of quote that deserves to be on a T-shirt or on your favourite mug. This is just one of many exclamations from the Zoo’s ectotherm team leader Dave, whose enthusiasm for the blue iguana is absolutely infectious.

Earlier this year Dave spent three weeks in the picturesque Cayman Islands, undertaking conservation fieldwork for the blue iguana (Cyclura lewisi), also known as the Grand Cayman ground iguana. Although extremely rewarding, this work is also crushingly brutal – with searing hot temperatures (38ᴼC), unforgiving terrain and long days in the field.

This head-starting programme (a conservation technique where endangered animals are bred and/or reared in human-care and then released into the wild) started off with humble beginnings, with tiny iguanas hatching out every few months from incubators in Fred’s office. The initial goal was to breed and release 1,000 iguanas to boost the struggling wild populations, with the project hitting this incredible milestone in 2018. As a direct result of this work, the blue iguana’s conservation threat status was downgraded from ‘critically endangered’ to ‘endangered’ on the IUCN Red List.

So, what is so special about the species? Blue iguana, affectionally called ‘iconic blue dinosaurs’ by locals, are endemic to these islands - meaning they’re naturally found nowhere else in the world. As its name suggests, the blue iguana is a sight to behold - ranging in colour from gray to dusky-blue, that increases in brightness and intensity during the mating season. The species feeds upon native vegetation including leaves, stems, fruits and flowers with occasional insects and fungi thrown in for a well-rounded diet.

Female iguanas dig their nest cavities roughly 30cm deep into the ground to deposit a clutch of 20 or so eggs. This nest is then covered over with a layer of soil, creating a nice warm space for the eggs to incubate, maintaining an ambient temperature of between 30-33ᴼC. After 60-90 days the young hatch and dig their way out – but sadly, these hatchlings are easy pickings for introduced predators like cats and dogs and their mortality rate is very high.

For the blue iguana that do survive, there is a raft of compounding issues, such as competition for resources from introduced grazing animals like goats and non-native iguanas. Fortunately, once they reach three years of age, they can see off most predators, except for dogs.

A gate-crasher to this island paradise is the green iguana (Iguana iguana), native to Mexico, Central and South America. It was introduced to these islands in the 1990s for the pet trade and as a food source for locals. Their introduction caused issues on multiple fronts; they not only compete for the same land and food resources as the endemic blue iguana, but they also harbour a deadly bacteria in their mouths - Helicobacter. While green iguanas have evolved to live with this bacteria, it proves fatal for blue iguanas who come into contact with it.

In 2018, the Cayman Island’s Department of Environment coordinated an initiative to reduce green iguana populations on the islands, providing training for local Caymanians in humane culling practises. Within three years, the programme successfully removed a total of 1.2 million green iguanas across the islands and it was estimated that just 25,000 remained. Unfortunately, due to a variety of factors including interruptions during the COVID-19 pandemic, the green iguana population has increased again, to around 87,000 individuals, and new creative methods are needed for halting their population growth.  

Luke Harding Is the Blue Iguana Conservation Programme Manager at the National Trust for the Cayman Islands, and heads up the Blue Iguana Recovery Programme. Every year, surveys are undertaken to understand how the wild iguana populations are faring.

This was the second time Dave was able to help this vital project and says the best piece of advice he received was to, “get comfortable with being really uncomfortable.” Blue iguanas have adapted to live in this inhospitable and harsh environment, and at the extremes of their ecological niche, in order to survive. They can dart across this landscape with ease, while for mammals it’s another case entirely. Walking across these jagged ‘rock daggers’ for 21 days was enough to rip through two brand new pairs of boots and a pair of trainers! But thankfully, Dave went prepared.

Carrying out this survey work requires three separate teams of people, walking nine separate transects (a marked ‘line’ that cuts through a landscape and allows for standardised measurements or observations to be taken) each day. The teams walk three transects in the morning and three in the afternoon, switching between the different lines to avoid any potential data biases. The teams were made up of herpetologists from around the world – Edinburgh Zoo, London Zoo, Jacksonville Zoo, Bronx Zoo, Philadelphia Zoo and Paignton Zoo.

Shouldering a heavy backpack each morning, the teams headed out at around 6am for what would be an eight-hour day in the field. This included carrying 3-4 litres of water each, as keeping hydrated is very important to avoid the risk of fainting, or worse. Creeping through the scrubland silently (the transect paths are cleared of vegetation in advance of the monitoring), a quiet hush falls around them. Once they reach their destination, the team wait for an hour to ensure the area becomes sufficiently quiet for the iguanas to make an appearance.

Then it is a process of watching and waiting – with each team recording any individuals they see. Blue iguanas that have been bred and released through the recovery programme are given individual-coloured beads attached to their crests to help identify them. If no bead is present the team look for evidence of a ‘bead scar’ or determine if the iguana is likely a wild-born individual. They also note down other key descriptors such as their size, sex and distinguishing features like a floppy crest, scars or other injuries.

Large mature males can become so big that their crest can flop over due to its own weight - what Dave describes as “an absolute tank of a male!”. It can take 30 or so years for a male to reach this size, and blue iguanas are known to live up to 50 years – but they could live even longer than this.

During the survey, each team sighted roughly 4-6 iguanas per day, with the highest being 10 iguanas in one day. There were however, two ‘friendly’ females that were so habituated to humans that they had to be excluded from the study data!

Not only is the heat and topography challenging, but Dave says, there are also many plants to avoid. The reserve is full of cactuses that splinter when you touch them, there is an array of sharply pointed succulents, shrubs that will give you a rash (the lady hair - Malpighia cubensis) or even cause your skin to blister (maiden plum - Comocladia dentata) if you brush up against them. The most frightening is the manchineel, also known as manzanilla de la muerte or ‘little apple of death’, as it’s one of the most dangerous plants in the world – a toxic-sap is present in the fruit, leaves and bark of the tree, and if you sit underneath when it’s raining it will cause your body to go into shock. Essentially, Dave enthuses, “most of the plants in the reserve want to kill you!”.

On Dave’s first trip to the islands in 2020, a hatchling was rescued from the QEII highway and was taken to the blue iguana facility for its safety. Dave was given the privilege of naming this iguana for his contribution to the programme that year and he gave her the name Willow. Three years later on Dave’s return, he was able to release this young sub-adult female back to the wild.

“Releasing a blue iguana is one of those bucket list items and to have done this with an animal I have cared for is truly special. It feels incredible knowing that she is out there contributing to the next generation of iguana on the island,” explains Dave. 

“It’s an absolute privilege and a pleasure to be invited to be part of this work. If I was to speak to myself when I was 16 years old, I never could’ve even imagined that I would be part of an annual population census for Grand Cayman blue iguana – which is an animal I’ve been aware of, as a conservation flagship species, for such a long time. It’s really one of those career affirming moments and it’s beyond special to be given the opportunity to do this.” 

Many of our animal and veterinary staff are so passionate about what they do, they will volunteer for projects outside of their Zoo roles. This was the case with Dave, who took annual leave to participate in this work, with the National Trust Grand Cayman kindly sponsoring his trip.

This is something the programme appreciates immensely, with Luke explaining, “Volunteers have been at the heart of our success throughout the history of the programme. The dedication that so many individuals have shown to give up their time, expertise and often at their own expense, is a key factor in what has made this programme so successful. I thank Dave and all the other herpetologists for their tireless support of our work.”