Research

Knob-headed Giant Gecko Rhacodactylus auriculatus

Conservation status: Lower risk - least concern

Description: A large species of gecko growing to a body length of 125 mm with a tail that measures up to 90% that of the body. It has moderately broad toes and the head has a series of raised crests on the skull that give the gecko a 'knobbed' or 'horned' appearance. It has large plate like scales on the head and neck, and a distinctive groove running from the corner of the mouth towards the ear. The colour pattern highly variable from mottled to having a broad bars running down the body.

Natural distribution: Moderately widespread throughout the south of Grande Terre, and from isolated ultramafic peaks on the northwest coast.

Distribution within Province Nord: Recorded from ultramafic peaks in the far north of the island, and from peaks along the north-west coast.

Ultramafic - rocks that are dominated by minerals high in magnesium and iron, and which tend to be dark-coloured rather than pale.

Distribution within Province Sud: Restricted to Province Sud and ranging in distribution from the very south of the island north to Mt Do. There is a large gap between Mt Ouin and Sarramea where no records appear, which reflects a lack collecting in both coastal lowlands and the ranges in this area.

Threats:

• potentially extensive loss or degradation of maquis shrubland ( low, heath-like vegetation) and closed forest edge habitat through activities associated with mining. Particularly in isolated high elevation forest and gully forests affected by mining spoil
• potentially high level of threat to populations in closed forest edge habitat with high infestation levels of introduced fire ants (Wasmannia auropunctata) causing significant decline in abundance
• a moderate but widespread decline in quality of maquis and closed forests edge habitat through repeated firing
• moderate level of threat from exotic pests such as rats, cats and pigs (predation of adults, young and eggs) particularly in closed forest habitat adjacent to urban development
• localised but potentially intensive decline in area, extent and quality of maquis and closed forest habitat adjacent to urban development
• potentially intensive threat to localised population by the collection for illegal trade at readily accessible sites

Conservation status: Secure. Rhacodactylus auriculatus occurs at 17 locations representing up to 13 subpopulations over the south of the island, and a number of geographically distant populations in the far north-west. The distribution of the species as it is known satisfies the criteria for a small distribution (area of occupancy <1,000 km2), but is likely to be recorded from additional locations with further survey work.

The species occurs in maquis shrubland and closed forest edges bordering maquis. It has not been recorded from the interior of well-developed closed forest habitat except where access roads are present. Its occurrence in both habitats indicates a likely degree of connectivity between at least some of the subpopulations identified, and the potential for recolonisation if once extinct. Threats leading to a continuing decline in both closed forest and maquis shrubland habitat have been identified above, but large areas of potentially suitable habitat, subject only to minimal or no disturbance, occur within the species range. For these reasons R. auriculatus does not satisfy the criteria required to place it at a greater level of threat and most appropriately categorised as Lower Risk - least concern - it is not considered to be under any immediate threat.

Future research required: none specifically recommended.

• general survey work in closed forest and maquis shrubland from Mt Vulcain north to Mt Sindoa to determine the distribution of the species in that area
• survey to determine the presence of isolate (and potentially genetically unique) populations in disjunct maquis and closed forest patches on ultramafic substrate between Thio and Houailou

Copyright © Australian Museum, 2002