Christmas Island covers an area of about 135 square kilometres, consisting of a large central plateau surrounded by a series of steep cliffs, terraces and slopes.
Five native terrestrial reptile species occur on the island, 4 of which are endemic. A sixth species that was endemic became extinct in 2014—Christmas Island forest skink (Emoia nativitatis). Five terrestrial reptile species have been introduced to Christmas Island (Smith M et al. 2012).
In the past 20–30 years, 4 of the remaining 5 species have declined significantly ; 2 are listed as critically endangered under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act; Christmas Island blue-tailed skink—Cryptoblepharus egeriae, and Lister’s gecko—Lepidodactylus listeri), and 1 is listed as endangered (Christmas Island giant gecko—Cyrtodactylus sadleiri). The coastal skink (Emoia atrocostata) has not been recorded in the wild since 2004 (it is not currently listed under the EPBC Act), the blue-tailed skink was last recorded in the wild in 2010, and Lister’s gecko has not been recorded since 2012 (Webb et al. 2014). All were recorded as abundant in 1979 (Cogger et al. 1983). A fourth species, Christmas Island blind snake (Ramphotyphlops exocoeti), has been recorded so infrequently that the data are insufficient to assume a decline; it is listed as vulnerable under the EPBC Act.
Captive breeding programs have been successful for blue-tailed skink and Lister’s gecko; by late 2016, more than 890 blue-tailed skinks and more than 700 geckos were in captivity on Christmas Island and in Taronga Zoo. However, the future of these species remains uncertain, since the processes threatening their persistence in the wild are not well understood (Webb et al. 2014). The success of the breeding program has provided the opportunity for the trial release of blue-tailed skinks into predator-proof compounds on the island to help assess effectiveness of predator control.
Predation by introduced predators is thought to be the key factor in the decline of native reptiles on Christmas Island. Many known reptile predators have now been introduced to the island, including the domestic/feral cat (Felis catus), house mouse (Mus musculus), giant centipede (Scolopendra subspinipes), red jungle fowl (Gallus domesticus), yellow crazy ant (Anoplolepis gracilipes), Asian wolf snake (Lycodon capucinus), black rat (Rattus rattus), and barking or house gecko (Hemidactylus frenatus) (Smith M et al. 2012).