Sister Islands Rock Iguana
Cyclura nubila caymanensis
IUCN Status: Critically Endangered
Range: Little Cayman and Cayman Brac, Cayman Islands
Population: ~2,000–4,000
Size: Males: snout to vent length up to 2 feet, 24.3 pounds. Females: snout to vent up to 1.6 feet, 10.5 pounds.
Threats: Habitat destruction from road construction and development; feral and free roaming cats and dogs; road mortality.
Conservation Measures

This Critically Endangered subspecies of Cyclura nubila is found only on Little Cayman and Cayman Brac – two small islands situated about midway between Grand Cayman and Cuba. Due to its relatively undisturbed quality, Little Cayman supports the more robust population of Sister Islands Rock Iguana, while the comparatively developed Cayman Brac hosts an extremely reduced population (<200 mature adults). Both populations are suspected to be in decline, with expanding island development exacerbating pressures of habitat degradation, predation by feral mammals, road traffic, and interaction with non-native species.

In 2012, following a 3-year study by the Durrell Wildlife Conservation Trust, the Little Cayman National Trust (LCNT) purchased a major communal nesting site on the west end of Little Cayman (Preston Bay) and began distributing “Iguana Crossing” signs at high traffic areas around the island in cooperation with the Cayman Islands Department of Environment (DoE). Road mortalities alone are estimated to kill at least 100 iguanas annually on Little Cayman. A team from Mississippi State University renewed research efforts in 2015 in collaboration with the DoE and San Diego Zoo Institute for Conservation Research. The main objective of this IIF-funded study is to assess current population trends and predict how future breeding and habitat use patterns may contribute to long-term viability, based on molecular and ecological evidence. In August 2016, a hybridization event between a male Rock Iguana and a non-native female Common Green Iguana raised new concerns about biosecurity on Little Cayman. A local program of the LCNT, Green Iguana B’Gonna, has been working diligently since 2012 to raise public awareness and eradicate this invasive species on Little Cayman. Government funding has also been allocated to mitigate biosecurity issues between all three of the Cayman Islands.
The last intensive survey of Cayman Brac was conducted in 2012, finding about 80 adult iguanas patchily distributed across the island. Growing numbers of feral cats, dogs, livestock, and invasive Common Green Iguanas, along with frequent road mortalities and destruction of coastal nesting sites severely threaten this population’s long-term viability. Ongoing efforts headed by the Cayman Brac National Trust, the DoE, and collaborators are aimed at raising public awareness, identifying remnant nesting sites, and evaluating population genetic health. In addition, the DoE is working closely with local police on both islands to mitigate the threat of road mortality and actively support the new Brac Wildlife Rehab Group initiative.
Reports from the Field
IIF Grants Received