Annually during February, the middle of the dry season, numbers of female Iguana iguana gather to nest in a small clearing on the tiny islet of Slothia in Gatun Lake, Panama Canal Zone. Nesting takes several days to a couple of weeks for each female. She spends the first days testing sites and digging only for brief periods. She then begins to dig more intensively and excavates a burrow of 1-2 m in length and 1/4 to 1/2 m in depth. The eggs are laid and the burrow filled with dirt and then dirt is scraped towards it and nearby holes are filled. This filling may occupy a couple of additional days. Slothia provides protection for the iguana nests from the many egg eating predators that occur on the adjacent areas where the iguanas spend most of the year. Presumably this provides an important advantage to using such sites even though females frequently interfere with one another during nesting. A digging iguana is frequently supplanted from her partially finished nest burrow and even more frequent are unsuccessful attempts at supplanting. A female after laying often attempts to fill nearby burrows, even those actively excavated. A female in making her nest burrow may dig into an already completed nest and dig out the eggs that are ignored by the iguanas but eaten by waiting vultures. About a third of the females were recognizable as individuals and using these as a basis the number of female iguanas nesting on Slothia in 1967 was estimated at between 150 and 200.