The blue iguana is found only on Grand Cayman, a tiny, rocky island in the British West Indies. It can grow to 5 feet long and eats a vegetarian menu of leaves, flowers and fruit. During the mating season, hormones turn the males electric blue while the females brighten to powder blue.

Preferring a solitary life, females will ferociously defend fixed territories, while males tend to casually roam around or bask. The pace quickens in spring, when males chase or battle one another over females. Once a female is fertilized, she will burrow until she finds the perfect conditions for building a nest, then ram her way back out and disguise the nest with soil and debris. Each juvenile arduously opens its shell over a prolonged period. Once all the hatchlings are out of their shells and have regained their strength, they thrust through the soil in a single line and scatter into the undergrowth.

Cars, cats and dogs, and habitat loss are among the blue iguanas’ biggest killers. Shedd Aquarium is one of 10 U.S. institutions trying to breed these vanishing iguanas for release into protected reserves on Grand Cayman. Long off exhibit, our pair, Marley and Eleanor, moved into a new 1,200-square-foot rocky habitat in Waters of the World in 2005. Not only do visitors have a better view than in the wild, but learning about them is a powerful means to help prevent their extinction.