Research

Crested Giant Gecko Rhacodactylus ciliatus

Conservation status: Vulnerable

Description: A moderately large species of gecko growing to a body length of 130mm with a tail approximately as long as the body. The most distinctive feature is the row of elongate soft spiny scales either side of the head and neck from the behind the eye to just above the shoulder forming a raised crest. The colour is highly variable, ranging from a uniform light to dark brown or a broad pale vertebral stripe consisting of a series of large, broken blotches.

Natural distribution: Known from a few scattered locations in the central and southern regions of the main island, Ile des Pins, and Belep Islands.

Distribution within Province Sud: On the main island recorded from Riviere Bleue in the vicinity of Pont Germain and the adjacent Pourina river valley (part of the Resérve Spéciale de Fauna de la Haute Yaté), Mt Koghis, and Mt Ouin. Also from Isle des Pines, but not its offshore islands.

Distribution within Province Nord: Known from the Belep Islands off the northern tip of the main island, and possibly the east coast based on historical records in the late 1800's from 'Kanala'.

Threats:

• potentially high level of threat to closed forest populations on coastal lowlands of the Ile des Pins from subsistence agriculture resulting in a decline in area of occupancy and fragmentation of once continuous habitat
• potentially high level of threat to low elevation closed forest populations on the main island and Isle des Pines from high infestation levels of introduced Fire Ants (Wasmannia auropunctata) causing significant decline in abundance
• potentially high level of threat to closed forest populations on the main island through repeated firing of adjacent maquis habitat resulting in a decline in area, extent and quality of closed forest habitat and its edge
• potentially high level of threat to closed forest populations through activities associated with mining, resulting in a loss of, or degradation to, closed forest habitat, particularly isolated high elevation forest and gully forests affected by mining spoil
• potentially high level of threat from exotic pests such as rats and cats (predation of adults, young and eggs)
• localised but potentially intensive decline resulting from collection for illegal trade at readily accessible sites

Maquis habitat - low and heath-like vegetation

Conservation status: Rhacodactylus ciliatus has been recorded at only four locations in the south of the main island in closed forest habitat or adjacent edge vegetation. Three of the four locations are part of a single forest block and represent a single large sub-population, while the Mt Koghis sub-population represents a much smaller geographically proximate outlier. Recent studies show significant genetic sub-structuring between individuals from Mt Ouin and Riviere Bleue, indicating the possibility of some degree of fragmentation within that sub-population. The Isle of Pins and Belep Island populations each also represent a discrete sub-population.

The species distribution is small and comprises at least three widely disjunct sub-populations with a total area of occupancy of <500 km2. It could be recorded from additional locations within the sub-population on the main island, but the species overall range and area occupancy is unlikely to change significantly. These factors in combination with the range of threats identified above indicate the species can conservatively be categorised as Vulnerable, and could be moved to a higher level of conservation concern given the intensity of those threats.

It is possible sub-populations on the Belep Islands and Ile des Pins could each be placed at a higher level of threat given their small range and the number of potentially high level threats to insular sub-populations.

Future research required:

• undertake targeted survey work on the sub-population on the main island to determine its distribution, and degree of habitat fragmentation
• undertake targeted survey work on the sub-population on the Isle of Pines to determine its preferred habitat on the island and the extent of threat posed by land clearing on the preferred habitat
• determine the levels of infestation of introduced fire ants at low elevation sites, particularly the island sub-populations, and monitor population trends for the species at these locations
• research the biology of this species to determine basic life history parameters and habitat requirements
• assess the extent of decline in area and/or quality of sclerophyll forests on the Belep Islands sub-population with regard to the impact of fire on the forest edge

Copyright © Australian Museum, 2002