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Land Iguanas
In 1959, the status of the extant populations of land iguanas was considered good. Then in 1975, two populations on different islands (Cartago Hill on Isabela and Conway Bay on Santa Cruz) were decimated in less than six months by feral dog packs. Unlike tortoises, adult iguanas are not predator proof. Saving them meant removing them from their natural habitat until dogs were eliminated.
A breeding and rearing center was quickly established, but it was not large enough for all of the adults. A management technique, used only once before in Galapagos back in the 1930s, was implemented. Thirty-eight iguanas, about half of the original group of Santa Cruz iguanas brought to the center, were released on the small islets of Venecia off the northwest coast of Santa Cruz. This semi-captive population lived under natural conditions, but the islets had no large areas suitable for nesting. Approximately 100 m3 of soil were moved to Venecia from Santa Cruz and an artificial nesting area built. The population thrived. The iguanas on Venecia breed and reproduce and juveniles are then repatriated to Santa Cruz.
The knowledge gained in the tortoise center was applied to the iguana center. However, iguanas are much more difficult to maintain and breed in captivity. Research on iguanas, both in the field and in the center, and the resulting management practices were critical to the success of the program. Of primary concern were the physical conditions of the cages and incubation techniques, including temperature and water potential of the substrate. Through research the best techniques were quickly developed.
Nutritional Problems and a Successful Diet
However, by the 1990s, the captive land iguanas were in poor condition and not breeding. An animal nutritionist was brought in to review the possibility of nutritional problems. He developed a prepared diet for the iguanas based on previous work with green iguanas, using lentils, quinoa, vitamins, minerals, and other ingredients. Within a short time, the iguanas became healthier and mortality rates declined.
The Problem of Introduced Species
Unlike tortoises, the young land iguanas could not be repatriated to their original habitat unless the introduced predator problem was solved. Dogs eat adult as well as young iguanas, while cats eat only young animals. Once feral dogs had been eliminated on both southern Isabela and northwestern Santa Cruz, iguana repatriations were generally successful (see table below). Today, both of these populations appear to be healthy. However, cat control trips are carried out periodically to ensure successful recruitment into the population.
Successful Repatriations
Due to the survival of repatriates and the re-establishment of healthy populations, both the Cartago Bay and the Cerro Dragón land iguana programs were terminated in the 1990s. The last repatriation to Cerro Dragón from the center was in 1991, while the last repatriation to Cartago was in 1993. Transfers of young iguanas from Venecia to Santa Cruz continue to occur every three years.
Number of land iguanas repatriated by population and decade, 1982 to 2007.
| POPULATION | _.1980 | _.1990 | _.2000 | _.TOTAL |
|---|---|---|---|---|
| Cartago Bay (Isabela) | 324 | 70 | 0 | 394 |
| Cerro Dragón (Santa Cruz)* | 184 | 111 | 101 | 396 |
| Baltra | 0 | 94 | 252 | 346 |
| TOTAL | 508 | 275 | 353 | 1136 |
Source: CDF files.
* Cerro Dragón population includes repatriations to Conway Bay, Cerro Dragón, and Cerro Montura, all on the northwest corner of Santa Cruz. Some of the repatriated iguanas in this population were transferred from the semi-captive population on Venecia.
The Land Iguanas of Baltra
The land iguanas of Baltra have a very different history. Historically, the Baltra iguanas were the largest in the archipelago. However, when the Hancock Expedition visited the island in 1932 and 1933, the iguanas appeared malnourished. Introduced goats had devastated the vegetation. North Seymour, the island to the north of Baltra, had no land iguanas and no goats. In an attempt to help the iguanas, members of the Expedition transferred 70 iguanas from Baltra to North Seymour. Within 20 years, the iguanas on Baltra disappeared due to a combination of habitat destruction resulting from the construction of the U.S. Air Base in World War II, direct predation by dogs and cats, and competition by feral goats. The informal experiment of the Hancock Expedition in 1932-33 had saved the Baltra land iguana from extinction – but they were now on the wrong island.
In the 1980s, iguanas from North Seymour (where the population seemed to be in decline) were brought to the breeding and rearing center, with the idea of eventually repatriating the young to Baltra. Given that Baltra has two military bases, Air Force and Navy, iguana repatriations required the collaboration of not only the CDF and the GNPS, but also the Ecuadorian Armed Forces. The first 35 young iguanas were released in June 1991.
By 2008, the Baltra population was considered sufficiently healthy to allow the termination of the Land Iguana Program in captivity. To date, 420 iguanas have been repatriated to Baltra and their survival rate appears high. Recent surveys have shown that both populations, Baltra and Seymour Norte, are healthy and increasing.
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