Breeding Rare and Endangered Iguanas

How Duncan Malcolm MacRae, founder of Rimba Reptile Park in Bali, turned three decades of reptile-breeding expertise toward the ex situ conservation of rare and endangered iguanas.

My reptile journey did not end with the discovery of Varanus macraei. In the years that followed, my attention gradually turned toward a quieter, more deliberate kind of work: breeding some of the world’s rarest and most endangered iguanas. It has become one of the most meaningful chapters of my life with reptiles.

From Commerce to Conservation

Although my focus had shifted, I certainly hadn’t left my interest in reptiles behind. Over the last 10 years, I gradually began building a carefully selected collection of iguanas and other iguanids from different parts of the world. This time, however, my objectives were somewhat different.

Many of the species I became interested in were endangered or critically endangered in their natural habitats. Rather than approaching breeding purely as a commercial enterprise, I became increasingly interested in the role that experienced private breeders could potentially play in maintaining genetically healthy ex situ populations.

It is a shift that reflects a wider movement within the iguana conservation community itself. The family Iguanidae today comprises around 46 living species, spread from the deserts of the American Southwest to the islands of the Caribbean, the Galápagos, and the South Pacific — and the great majority are now considered threatened with extinction. Organisations such as the IUCN SSC Iguana Specialist Group, formally recognised in 1997, and the International Iguana Foundation, founded in 2001, exist precisely because of how quickly wild iguana populations can decline, and how much coordinated effort is needed to reverse that trend.

The Grand Cayman Blue Iguana (Cyclura lewisi) is often held up as the clearest example of what this kind of coordinated breeding effort can achieve. By 2002, fewer than 25 individuals remained in the wild, and the species was considered functionally extinct as a self-sustaining population. Through a sustained captive breeding and headstarting programme run by the National Trust for the Cayman Islands, more than 1,200 captive-bred and head-started iguanas have since been released back into protected areas, and the species was downlisted by the IUCN from Critically Endangered to Endangered in 2012. It remains one of the strongest arguments for exactly the kind of ex situ work I have committed myself to.

My Own Ex Situ Breeding Programme

Today, much of my reptile work is focused on successfully maintaining and breeding rare and endangered iguana species. For endangered animals, I believe it is extremely important that healthy and genetically diverse populations exist outside their natural habitats as well as within them.

Wild populations can face enormous pressures: habitat destruction, invasive species, natural disasters, climate change and other unexpected events can sometimes devastate a species within a relatively short period. A properly managed ex situ population can therefore represent an important additional safeguard.

The ultimate goal must always be to protect species in their natural habitats. But maintaining healthy populations outside those habitats can potentially provide valuable genetic reservoirs and, where appropriate and scientifically managed, animals that may one day contribute to conservation breeding or reintroduction programmes. This approach mirrors the “headstarting” technique used across many in situ iguana projects, in which hatchlings are raised in a protected environment until they are large enough to withstand the predators and pressures that would otherwise overwhelm them in the wild — a method that has already helped pull several critically endangered Caribbean rock iguanas (genus Cyclura) back from the brink.

I have now been working with a number of rare iguana species for many years, and I have been fortunate to achieve consistent breeding success with several of them.

None of that success has come quickly. Most iguanas do not reach sexual maturity until somewhere between two and four years of age, and the larger rock iguanas of the genus Cyclura often take longer still. Rushing a pairing before an animal is genuinely ready rarely ends well, and over the years I have come to treat patience as one of the most valuable tools in the collection.

Getting animals into breeding condition at all depends on recreating the seasonal cues they would experience in the wild: gradual shifts in photoperiod, temperature and humidity that signal the approach of a breeding season, followed by the right nesting conditions once eggs are due. Even then, techniques that work well for one species can fail for another. Husbandry data compiled for the West Indian rock iguanas shows real differences in incubation temperature and duration between species — some clutches need roughly 80 to 90 days at around 28–29°C, while others are naturally suited to warmer, longer incubation periods — and the Lesser Antillean iguana, Iguana delicatissima, is considered enough of a husbandry outlier that it is generally kept and managed quite separately from its Caribbean rock iguana relatives.

Even pairing compatible individuals is not simply a matter of putting a male and female together. Recent research on Caribbean rock iguanas has found that allowing animals the chance to become socially familiar with one another before breeding, rather than pairing them cold, measurably improves reproductive success — a finding that matches what I have observed working with my own collection over the years.

It is enormously rewarding. The excitement of seeing a rare species reproduce successfully never disappears — particularly when you know just how vulnerable some of these animals are in the wild, and how much patience it took to get there.

Read more from the IUCN SSC Iguana Specialist Group and the International Iguana Foundation.

My interest in the natural world extends well beyond reptiles — it’s also what led me into ethnobotany and, eventually, to founding Motark Enterprise, a botanical sciences company. More on that on my About page.

Sources

• Bali Reptile Park (official website). Singapadu, Gianyar, Bali, Indonesia.
• National Trust for the Cayman Islands — Blue Iguana Conservation Programme.
• IUCN SSC Iguana Specialist Group — History.
• International Iguana Foundation — History.
• West Indian Iguana Husbandry Manual, IUCN SSC Iguana Specialist Group.
• Iguana iguana, Animal Diversity Web, University of Michigan.
• Blake et al., “Social opportunities and mate preference improve breeding success in Caribbean iguanas.” Scientific Reports (2023).