Land iguanas are very flexible in their diet but generally depend on low-growing plants and shrubs, as well as the fallen fruits and pads of catcus trees. These succulent plants provide them with most of the moisture they need during long dry periods. However, when whalers and settlers started visiting Galapagos in the early 1800's, they brought with them goats, pigs, dogs, cats and other domestic animals. Over time, many of these animals escaped or were abandoned, with drastic results. Cats hunt the young iguanas and dogs kill adults.
Goats wipe out entire areas of vegetation that the iguanas depend on for food.
Today, the abundant iguanas that Darwin wrote about on Santiago Island are extinct. On some other islands, they are nearly gone. In 1976, wild dogs wiped out a colony of almost 500 land iguanas at Conway Bay on Santa Cruz. Together, the Charles Darwin Research Station and the Galapagos National Park Service launched an emergency rescue operation for the 60 or so survivors. Shortly thereafter, another large-scale attack occured at Cartago Bay, Isabela, and thirty more iguanas were rescued.