Habitat use, distribution and population dynamics of the Maud Island frog, Leiopelma hamiltoni.

Abstract

The Maud Island frog, Leiopeima hamiltoni, is a rare, terrestrial species which occurs on Maud and Stephens Islands in the Cook Strait. The Maud Island frog population is generally restricted to a 16 hectare remnant forest stand. Systematic surveys of the forest habitat showed the frogs were not uniformly distributed throughout the forest. Higher densities occurred in the lower section of forest where the canopy was higher and rocks more abundant. Other habitat variables had less effect on frog distribution. The minimum population estimate based on frogs seen at night was approximately 6,400, though the actual number present in the forest remnant was estimated to be approximately 19,000. The minimum adult snout to vent length was 35.1mm (range: 35-50.5mm), while sub-adults ranged from 12-35mm. Adult weights varied from 4.5-10.9g and sub-adults from 0.3-4.4g. Most adult frogs were medium brown, with uniform or mottled patterns. Sub-adults were predominantly uniform, light or medium brown. Five adult and 16 sub-adult frogs had speckled green markings. The Maud Island frog is nocturnal and its activity (as measured by the number of frogs caught per night) was influenced by the amount of available moisture, with greater numbers of frogs emerging on nights with rain, or rain over the previous 24 hours. Frogs also climbed higher into the foliage on wet nights. On the two study grid sites, frog capture sites were correlated with rock substrate and the density of frogs was higher on the grid with the most extensive rock substrate (30-78 frogs/100m2 on Grid One and 85-185 frogs/100m2 on Grid Two).