Cryptic and complex nesting in the yellow-spotted monitor, Varanus panoptes

Despite the general importance of nest site choice in reproductive success in taxa with little or no parental care, little is known for reptiles other than turtles. Here we report on the nesting ecology of the Yellow-Spotted Monitor, Varanus panoptes, a large tropical lizard that utilizes warrens (concentrated groups of burrows) in northern Australia. We used radio-telemetry, remote photography, and the complete excavation of a warren to test the hypotheses that 1) warrens are used by multiple individual V. panoptes; and if so, 2) they are used for communal nesting; or alternatively 3) they are used for communal estivation during the dry season. At least six individual V. panoptes utilized the warren system including four females and two males, and burrows were excavated by both sexes. Excavation of the warren revealed no estivating lizards at a time when four radio-telemetered V. panoptes had begun estivation. However, we found two nests in the warren, indicative of either communal nesting or multiple clutches of the same female. Nests were deeper than that recorded for any other reptile and were structurally complex. We discuss the implications of the depth and structure of the nesting burrow for the thermal and hydric environment of the eggs and for hatchling emergence. The warren's usage by multiple individuals raises the possibility that the severe declines in V. panoptes caused by invasive Cane Toads (Bufo marinus) may have important implications for the V. panoptes social structure.