The habitat use and ecology of the harlequin gecko (Hoplodactylus rakiurae)

Abstract

The Harlequin gecko (Hoplodactylus rakiurae Thomas 1981) is an endangered species endemic to the southern third of Stewart Island. It is undoubtedly one of New Zealand's most spectacularly patterned lizards and one of the southern-most geckos in the world where its known range is between 47°00' - 47°17'S² (Whitaker, 1994). It is currently ranked as "low risk/not threatened" by the International Union for Conservation of Nature (IUCN, 2004) and it a species listed by CITES in Appendix 111. The species is ranked nationally "sparse" (Hitchmough, 2002; Molloy et al, 2002). This study investigated three questions that concerned H. rakiurae. 1. Was H. rakiurae associated with particular habitats and microhabitats? 2. Did biological attributes (e.g. body size, colour, reproductive strategy etc) vary with particular habitats along with other species in cooler areas of New Zealand? 3. Did distribution patterns of H. rakiurae vary with landscape distribution and environmental conditions?

H. rakiurae was studied at Harlequin Hill in Port Pegasus and 511 near Patterson Inlet. Line transects sampling within plots were designed to measure densities of the geckos. To assist with determining habitat use, activity patterns and thermal preferences, detailed descriptions of the gecko's micro- and macrohabitat and environmental factors were made. Information was collected on body size and palpation of females provided information on clutch size and reproductive cycle. Each gecko captured or recaptured was weighed, measured, and photographed. All geckos captured were permanently marked. Gecko scats were collected to determine dietary components. Rodent index lines were established at Harlequin Hill to determine numbers and impact of rodents in the area.

The capture of 29 H. rakiurae during the study from November 1999 to October 2001 at Harlequin Hill and 511 revealed aspects of the species ecology and biology that provides baseline data for future studies and monitoring surveys of H. rakiurae. 17 surveys between 1999 - 2001 to Harlequin Hill and 511 showed low densities of the geckos at the study sites. H. rakiurae were scarce as a species on Stewart Island and as individuals at the particular study sites. Line-transect sampling found clumped spatial distributions of the species with some habitats (shrublands) consistently harbouring residents and other patches remaining unoccupied. Other locations around Stewart Island and surrounding islands were also surveyed but no geckos were found. Key features of the habitat H. rakiurae was associated with appeared to be sloping open mosaics of grassland, herbfield and shrub land in the low to upper subalpine zone on Stewart Island. The relationship between weather variables and gecko capture rates was relatively strong with the greatest number of geckos emerging when conditions were sunny and dry, especially during the spring and summer. H. rakiurae were observed basking or active during the day as well as being active at night. They were recorded in a range of ambient air temperature from 4 - 20°C. The pregnancy rate of females captured during 1999 - 2001 suggested a low reproductive output of 0.34 (females from Harlequin Hill) and 0.63 (females from 511) offspring/female/year Palpation of female H. rakiurae revealed a biennial or possibly triennial reproductive cycle and small clutch size as compared with mainland gecko species.