Galapagos Islands Lizards
Land iguanas are large — more than 3 feet long — with males weighing up to 30 pounds. They live in the drier areas of the Islands, and in the mornings can be found sprawled beneath the hot equatorial sun. To escape the heat of the midday sun, they seek the shade of cacti, rocks, trees or other vegetation. At night they sleep in burrows dug in the ground, to conserve their body heat. They feed mainly on low-growing plants and shrubs, as well as fallen fruits and cactus pads. These succulent plants provide them with the moisture they require during long, dry periods. Land iguanas show a fascinating symbiotic interaction with Darwin’s finches, as do giant tortoises, raising themselves off the ground and allowing the little birds to remove ticks.
Land iguanas reach maturity between 8 and 15 years of age. Males are territorial and will aggressively defend specific areas that typically include more than one female. Following the mating period, female iguanas find suitable nesting sites, dig their nesting burrow, and lay between 2 and 20 eggs. The female defends the burrow for a short time, to prevent other females from nesting in the same place. The young iguanas hatch 3-4 months later, and take about a week to dig their way out of the nest. If they survive the first difficult years of life, when food is often scarce and predators are a danger, land iguanas can live for more than 50 years.
In 1959, the status of the extant populations of land iguanas was considered good. Then in 1975, two populations on different islands (Cerro Cartago 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, in the 1930s, was implemented. Thirty-eight Santa Cruz iguanas, about half of the original group 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 was moved to Venecia from Santa Cruz and an artificial nesting area was built. The population thrived. The iguanas on Venecia continue to breed today and many of the resulting juveniles are repatriated to Santa Cruz, approximately every three years.