Mona ground iguana

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The Mona ground iguana, also known as Cyclura stejnegeri, is a critically endangered rock iguana that lives only on Mona Island, Puerto Rico. It is one of the island’s few large land animals and the largest native terrestrial lizard in the area. Some scientists view it as a separate species, while others consider it a subspecies of the rhinoceros iguana.

Appearance and behavior
This is a large, heavy lizard with strong legs and a tail that can be flattened vertically. It has a crest of horned scales from the neck to the tail. Adults are gray to olive in color, with a bit of brown or blue tint. Males have distinctive horns on their snouts, a helmet-like area on the head, and large dewlaps. Juveniles have gray bands across their bodies. The iguana is diurnal, meaning it is active mainly during the day and often basks in the sun to conserve energy.

Habitat and range
The Mona ground iguana is found only on Mona Island. It spends a lot of time underground in talus slopes, caves, and sinkholes, sometimes more than a meter below the surface. Most of the island is unsuitable for nesting; nesting sites are limited to a small sandy area on the southwest coast that gets direct sunlight.

Diet and ecological role
Like other Cyclura iguanas, it is mostly herbivorous, eating leaves, flowers, berries, and fruit. Seeds that pass through its digestive system can germinate more quickly, helping plant life spread across the island. Because it is one of the island’s largest herbivores, it plays an important role in shaping the vegetation and ecosystem.

Reproduction and life cycle
Males reach sexual maturity around 3–4 years old, and females about a year later. The mating season begins in early June, and females may mate with several males over a two-week period. About a month after mating, females dig nests up to 0.91 meters deep and lay 5–19 eggs (about 12 on average). The eggs incubate in sun, and hatch after about three months. Hatchlings are around 32 centimeters long and weigh about 74 grams, growing about 5 centimeters per year.

Population and threats
Current estimates put the population at around 1,500 individuals, with lower densities than some other iguanas in the region. The species is aging, and numbers are in decline. The biggest threats come from invasive animals, especially feral pigs that root iguana nests. Goats also damage habitat and compete for food, while feral cats prey on young iguanas.

Conservation efforts
A headstarting program began in 1999, led by the Puerto Rico Department of Natural and Environmental Resources with partners from the IUCN, the US Fish and Wildlife Service, the Toledo Zoo, and the University of Puerto Rico. The program raises young iguanas in a safe setting until they are large enough to survive in the wild, then releases them. Health screening and medical care are also part of the program to monitor the species’ well-being and plan for future protection.