“It’s heaven for them,” says Young, who works on iguana conservation for the Virgin Islands National Parks Trust.
The 10-mile island has fewer than 300 residents and is best known for its vast coral reef, sandy beaches and flock of flamingos.
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For millions of years, iguanas – up to five feet long and 15 pounds – were the largest vertebrates in this landscape. Although the adults are ferocious, the iguanas have been brought to their knees by unlikely predators – feral cats that prey on juveniles.
Unlike the overabundant green iguana, which is native to Central and South America and widely introduced elsewhere, there are extremely few Anegada rock iguanas. By the 1990s, the pre-established population of around 10,000 iguanas had dropped to around 200. A simple conservation strategy has since doubled the population. But the recent setbacks show the limits of the work.
Iguanas are particularly vulnerable when hatching from eggs buried in sandy nests. Kelly Bradley, a conservation biologist at the Fort Worth Zoo who has worked with these iguanas since 2001, estimates that up to half of the juveniles are eaten in their first week by native snakes and birds – Puerto Rican runners and American kestrels.
It’s natural, these animals have evolved together for thousands of years. What tipped the scales were the non-native feral cats being effective predators. They eat baby iguanas like popcorn, and very few iguanas survive to adulthood.
The cats likely arrived with settlers in the 1700s and spread across the island. They have no natural predators, and as their numbers increased, the iguana population declined to a critical level that required human intervention.
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Near the cliff, Young beats a few meters in the thorny brush, scanning the ground. He soon finds a horseshoe-shaped scrape in the sandy soil. It doesn’t look like much, but it’s an old nest, where an iguana laid her eggs last year.
Each summer, he and Bradley painstakingly search for new nests dug by the iguanas – tunnels leading to deep chambers where they lay their eggs. It can take days to find even one nest.
When they find a nest, they place large steel hoops to trap emerging hatchlings, more than 40 in a good year. They bring them to an “advance” facility, cages where they are raised for several years until they are big enough to defend themselves against cats. They are then released back into the wild.
Limits of human intervention
The program released 274 iguanas. Bradley tracked dozens of them via radio, and more than 80% survived the first two years after release. But as long as cats remain abundant on Anegada, Bradley says iguanas will be a “conservation-dependent species” – one whose survival depends on human intervention. Recent events show the limits of such intervention.
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In 2017, Hurricane Irma hit Anegada just before trapping season. The team did not capture any juveniles that year. Then, while the island was still recovering from the hurricane, the British Virgin Islands went into lockdown during the pandemic. Both events have limited Bradley’s fieldwork in recent years, and she and Young have collected fewer iguanas.
Walking among the cages at the original facility, Young says there have been up to 64 iguanas in captivity in recent years, but now there are 48. The facility is a project from the Virgin Islands National Parks Trust, with educational panels on iguanas and island flora and fauna. When four American tourists arrive, Young shows them around.
Young says an occasional visitor, who usually arrives barefoot with a small group of companions, is Richard Branson. The billionaire owns nearby Necker Island, one of many small islands with introduced populations of Anegada iguanas. Bradley says there are now more iguanas on these islands than on Anegada itself, but because they are all descended from just eight animals captured on Anegada in the 1980s, they lack genetic diversity, so their value storage is limited.
Tandora Grant, San Diego Zoo Wildlife Alliance conservation program specialist and Iguana Specialist Group officer, says that when most people think of iguanas, they only think of the green iguana, iguana iguana. Its abundance masks the rarity of its cousins. As a family, Grant says, iguanas are among the most endangered animals in the world.
“There are 45 different species of iguanas,” Grant explains, “and only one is the pest species that has been carried everywhere.”
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There are 10 species of iguanas in the genus Cyclura, all endemic to the Caribbean islands (another went extinct in the 1900s), and molecular analysis suggests they all descended from the rock iguana Anegada. When sea levels dropped during the ice ages, Anegada iguanas spread to other parts of the Caribbean, Grant says. When the seas rose again, these iguanas became isolated on islands and evolved into species that look distinctly different.
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Other Cyclura species in Jamaica and Grand Cayman also have starter programs to help them survive predation. These populations are growing, like that of Anegada. But without the programs, Grant says, everything would fall apart again.
“We need to keep doing this until all threats are truly and genuinely mitigated, which is why they depend on conservation,” Grant says. “If we could muster the money and the political will to wipe out all the cats in Anegada, we could go home.”
“Leaving is not a solution, it’s just a band-aid,” says Bradley. “We’ve doubled the population of Anegada, and that sounds good, but it’s not enough. The cause of the decline has not been removed or addressed.
The International Union for Conservation of Nature (IUCN) still considers the Anegada rock iguanas to be critically endangered and includes them on its “red list” of endangered species.
Cassander Titley-O’Neal, director of the National Parks Trust of the Virgin Islands, explains that an ongoing sterilization project aims to limit the cat population of Anegada. She does not envision a more ambitious cat control program at this time, but says iguana conservation is a long-term priority for the agency.
“The IUCN conservation status says it all,” Titley-O’Neal said. “They are critically endangered and must be protected for generations to come.”