A survey of native frogs (Leiopelma archeyi and L. hochstetteri) in Whareorino Forest, northern King Country

Abstract

Native frogs Leiopelma archeyi and L. hochstetteri were discovered in Whareorino Forest, northern King Country, in 1991. This thesis reports the results of a survey carried out there in 1993 to document the range, variation in habitat, local distribution and external morphology of these two species. Both species had a localised range of approximately 6 km2, and were broadly sympatric throughout this area. Nearly all L. hochstetteri were found in stream beds. L. archeyi was less restricted in its distribution, occurring from gullies to ridges, from in stream beds to far away from streams, and from under dense forest cover to no vegetative cover at all. The most important habitat factor affecting the distribution and abundance of L. archeyi was altitude, with most frogs found above 500 m asl, and abundance showing a positive correlation with altitude. L. hochstetteri was found mostly under stones. L. archeyi occupied daytime retreat sites under logs and stones, and amongst vegetation. Vegetative sites included those amongst hook grass (Uncinia sp.), rice grass (Microlaena avenacea), tree fern (Cyathea smithii) and crown fern (Blechnum discolor). Although a preference was shown for log sites, these sites were not common and 52% of L. archeyi were found sheltering amongst vegetation. Egg clusters of L. archeyi were also found in vegetation, as well as under stones. Snout-vent length in L. hochstetteri ranged from 16.7 to 43.7 mm, and weight from 0.6 to over 10 g. Dorsal colour was mostly brown, but there were also a few frogs with green colouration present. The brown colour ranged from light to dark. L. archeyi snout-vent length ranged from 11.5 to 38.4 mm, and weight from 0.2 to 5.2 g. Colour was very variable, ranging from brown through to patterned green and brown, to green, sometimes with conspicuous pink colouration along the flanks and at the bases of the limbs. The brown colour also ranged from light to dark. Relationships were found between L. archeyi size and colour, with pink colouration tending to be found more in smaller frogs, whereas larger frogs were more likely to be all-brown in their colouring. Larger frogs were also more often found under logs and stones than smaller frogs which predominated in vegetative sites, especially hook grass. A relationship between retreat site and dorsal colour is suggested. The introduced frog Litoria aurea and rats (Rattus sp.) preyed on L. archeyi. This causes concern for the future of Leiopelma in Whareorino Forest, and further investigation into the impact of these predators is needed. It is recommended that Leiopelma be monitored at several sites at Whareorino, with care taken to minimize disturbance of their retreat sites.